protocols for-predictable-aesthetic-dental-restorations

Protocols for Predictable Aesthetic Dental Restorations

Irfan Ahmad

Protocols for

Predictable AestheticDental Restorations

Protocols for

Predictable AestheticDental Restorations

Irfan AhmadBDS, The Ridgeway Dental Surgery, Middlesex, UK

Active member European Academy of Esthetic Dentistry

© 2006 I. Ahmad

Blackwell Munksgaard, a Blackwell Publishing Company,Editorial Offices:Blackwell Publishing Ltd, 9600 Garsington Road, Oxford OX4 2DQ, UK

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First published 2006 by Blackwell Munksgaard

ISBN-13: 978-14051-1820-0ISBN-10: 1-4051-1820-2

Library of Congress Cataloging-in-Publication DataAhmad, Irfan, BDS.

Protocols for predictable aesthetic dental restorations / Irfan Ahmad.p. cm.

Includes bibliographical references and index.ISBN-13: 978-1-4051-1820-0 (pbk. : alk. paper)ISBN-10: 1-4051-1820-2 (pbk. : alk. paper)1. Dentistry–Aesthetic aspects. 2. Prosthodontics. I. Title.[DNLM: 1. Esthetics, Dental. 2. Dental Restoration, Permanent.

3. Dental Restoration, Temporary. WU 100 A286p 2006]RK54.A46 2006617.6′9–dc22

2005024528

A catalogue record for this title is available from the British Library

Set in 10 on 12pt Sabonby SNP Best-set Typesetter Ltd., Hong KongPrinted and bound in Spainby GraphyCems, Navarra

The publisher’s policy is to use permanent paper from mills that operate a sustainable forestry policy, andwhich has been manufactured from pulp processed using acid-free and elementary chlorine-free practices.Furthermore, the publisher ensures that the text paper and cover board used have met acceptableenvironmental accreditation standards.

For further information on Blackwell Publishing, visit our website:www.dentistry.blackwellmunksgaard.com

Note: the author is an invited lecturer for many dental organisations but has no financial interestsand no formal links with any of these organisations.

Contents

Dedication viiiForeword by Ronald E. Goldstein ixPreface xi

1 Treatment planning – assessment,planning and treatment 1

Assessment 1Planning 3

Diagnosis 3Risk assessment 3Evidence-based decision making

and treatment 6Presenting treatment plan proposals

to the patient 9Treatment 11Clinical case study 12

Assessment 12Planning 13Treatment 16

2 The health, function and aesthetic triad 21

Health 21The periodontium 22Restorative implications 29Implants 29

Function 30Occlusion 30Phonetics 36

Aesthetics 37Facial composition 38Dentofacial composition 41Dental composition 45Gingival composition 48

3 Choice of all-ceramic systems 55

Scientific rationale 55Rationale for all-ceramic

restorations 55Physical and mechanical properties

of ceramic 58Uni-layer and bi-layer all-ceramic

systems 58Aetiology of fractures 59

Dental ceramics 60Silica-based ceramics 61Alumina-based ceramics 65Zirconia-based ceramics 68

Longevity 69Metal–ceramic 69Dicor and Cerestore 70IPS-Empress 1 70In-Ceram Alumina 70Procera 70Ceramic bridges (FPDs) 70

Clinical practice 73

vi Contents

4 Colour and shade analysis 77

Scientific rationale 77The stimulus for colour 78

The illuminant 78The object 79Sensation (the detector) 81Synopsis of the stimulus for

colour 83Perception 83Tooth colour determination 85

Physical variables 85Physiological variables 86Psychological variables 86Dental variables 87Other optical variables influencing

colour 89Shade guides 90

Types of shade guide 91Limitations of shade guides 93

Instrumental assessment 93Spectrophotometer 94Colorimeter 94Digital camera and red, green, blue

(RGB) devices 94Clinical practice 94Ocular shade assessment 95Instrumental shade assessment 96

5 Foundations and intra-radicular support 98

Introduction 98Vital teeth – scientific rationale 98Vital teeth 98

Retention 99Vital teeth – clinical practice 102Pre-assessment for cores on vital

teeth 102Radiographic evaluation 102Intra-oral evaluation 102

Clinical sequalae for cores on vital teeth 102

Non-vital teeth – scientific rationale 103Post materials 103

Casting alloys 103Prefabricated metal 103Ceramics 104Fibre 104

Criteria for intra-radicular post selection 106

Coronal dentine and the ferrule effect 106

Tapered vs. parallel 106Smooth vs. serrated 107Passive vs. active 107Direct vs. indirect technique 107Single- vs. multi-rooted teeth 109Choice of luting agents 109Aesthetics 110

Types of cores 113Modes of failure 114

Loss of retention 115Post fractures 115Root fractures 116

Pre-post placement assessment 117Endodontic factors 117Periodontal factors 117Choice of definitive

restoration 118Remaining coronal dentine 118Tooth location 118Summary 118

Non-vital teeth – clinical practice 118

6 Tooth preparation 125

Scientific rationale 125Reasons for extra-coronal

restorations 125Biologic width 127Margin location 128Margin geometry 130Preparation design 131Maintenance of dental hard tissue

integrity 133Cutting efficiency 135Clinical practice 135Anterior tooth preparation 135

Assessment 136Planning 136Treatment 137

Posterior tooth preparation 140Assessment 140Planning 140Treatment 141

Contents vii

7 Therapeutic temporary restorations 145

Introduction 145Scientific rationale 145Health 145Function 147Aesthetics 147Biocompatibility 151Strength 151Palliative 151Marginal integrity 152Preventing plaque accumulation 153Chromatic stability 155Handling characteristics and ease of

fabrication 155Material selection 155

Polymethyl methacrylate (PMMA) 156Polyvinyl ethylmethacrylate

(PVEMA) 156Bis-GMA resin 157Bis-acryl resin composite 157Urethane dimethacrylate (UDMA)

resin 157Clinical practice 157Fabrication 157Matrices 158

Existing anatomical form 158Proposed anatomical form 158Preformed metal and plastic

crown forms 159Techniques 159

Direct technique 160Indirect technique 162Direct–indirect technique 162

8 Biological impressions 165

Introduction 165Scientific rationale 165Secondary determinants 166

Stock vs. custom trays 166Inter- vs. intra-arch 166Closed vs. open tray 167One vs. two stages 167Passive vs. non-passive 168Warm vs. cold environment 168Manual vs. automated mixing 168Physical vs. chemical gingival

retraction 168

Impression materials 169Primary determinant 172

Patient factors (risk assessment) 173Operator factors 174

Clinical practice 177Dental biological impressions 177Gingival biological impressions 179

9 Try-in procedures 185

Clinical practice 186Extra-oral evaluation 186

Inspection of restoration on trimmed die 187

Inspection of restoration on untrimmed die 188

Intra-oral evaluation 189

10 Cementation and dentine bonding agents 191

Scientific rationale 191Types and properties of luting

agents 191Zinc oxide eugenol (ZOE) 191Zinc phosphate (ZP) 192Polycarboxylate (PC) 192Glass ionomer (GI) 192Resin-modified glass ionomer

(RGI) 192Dual-polymerisation resins (DR) 192Self-adhesive, dual-polymerisation

resins (SADR) 192Self adhesive, auto-polymerisation

resins (SAAR) 193Ceramic primers (CP) 193

Efficacy of cementing agents 193Adhesion 193Occlusal stresses 194Marginal integrity and leakage 195Retention 196Pre-treatment of abutment 197Dentine bonding agents 197Efficacy 201

Pre-treatment of intaglio surface 202Clinical practice 203

Index 211

Dedication

To my wife and soul companion, Samar, and my son Zayan.

Foreword

I have always thought that any teacher of beauty,including cosmetic dentistry, should have anartistic “eye.” In my opinion, Irfan Ahmad fallswithin this requirement. The first time I saw himlecture I was quite impressed with his under-standing and attention to all that is classified as esthetic. So, it is appropriate that Dr Ahmadhas authored Protocols for Predictable AestheticDental Restorations. His approach to basic andadvanced principles of esthetics is well grounded.Although each of us may have our own way ofdoing a particular procedure we should never-theless realize that there is more than one way toachieve the same goal and therefore Dr Ahmad’sunique approach to problems is well worth ourattention. His stunning photography is both cre-ative and educational, making step-by-step pro-cedures easier to comprehend. All too often wesee self-styled clinicians who both lecture andwrite as if they originated every single techniquethey show and with little or no evidence to backup their claims. Therefore it is refreshing to seethat Dr Ahmad relies on evidenced-based princi-ples to back up his artistic talent. The uniquenessof our profession is that we are not all “clones,”each of us has his or her own “tricks” or tech-nique to accomplish a common goal – that ofpleasing the patient and achieving both a func-

tional and an esthetic result. Thus it is bothrefreshing and a true learning experience to dis-cover Dr Ahmad’s unique way of how to accom-plish his esthetic goals.

It has been over thirty years since I wrote thefirst edition of Esthetics in Dentistry. This wasthe very first comprehensive textbook describingesthetic techniques both as an entity as well as avital part of interdisciplinary dentistry. Workingwith specialists for virtually all disciplines of dentistry, this concept has now been finallyaccepted into what we consider the prevailingstandard of care in both diagnosis and treatmentplanning.

Dr Ahmad understands this concept and thushe spends most of his text dealing with the detailsof how he, and we, should be achieving greatersuccess with all ceramic crowns and bridges. Justas I did in my first text, Dr Ahmad devotes achapter to each of the essential six steps to a suc-cessful restoration. There is an important lessonin spending an entire chapter on each step, andthat is not only to learn new tips on being moreefficient and seeing if another method is betterthan the one you currently use, but also that eachof the steps is a separate entity. This helps us con-stantly remember to spend an adequate amountof time with attention to detail, so that in the end

x Foreword

we will have done our very best in each phase ofthe restoration. It is this attention to detail thatcan make the difference between an ordinary andan extraordinary restoration. Dr Ahmad knows

this difference and I am so pleased he chose toshare that “difference” with all of us.

Roland E. Goldstein, DDS

Preface

The aim of this book is to furnish the clinicianwith knowledge for providing aesthetic dentalrestorations that are virtually indistinguishablefrom natural teeth. Dental aesthetics is intangi-ble, influenced by the wishes of the patient, ex-perience of the clinician, and the artistic andtechnical skills of the ceramist. Aesthetics lies inthe murky twilight between art and science. Artis not enough to create aesthetic restorations,while science alone is inadequate for pleasingresults. However, the clinical protocols necessaryfor aesthetic restorations are tangible, relying onbiological concepts combined with scientificresearch. Using the health, function and aesthetic(HFA) triad, the clinician and ceramist candeliver prostheses that are durable and har-monise with surrounding soft and hard tissues.The appearance of dental restorations is subjec-tive: one person’s Xanadu may be another’sInferno. Aesthetics is a passion, not a craft, andone that has to be sought rather than taught.According to Carl Jung, ‘A man who has notpassed through the inferno of his passions hasnever overcome them’.

The layout of the book is a chronological clinical journey, starting with treatment planningand ending with cementation. The interveningchapters between these start and end points

transport the reader through successive stages forproviding aesthetic dental restorations. Mostchapters commence with scientific rationale andfinish with clinical practice, applying theory to apractical scenario. Whilst the learning curve attimes seems onerous, once mastered the tech-niques can be expedited for making aestheticrestorations that are predictable, functional and long lasting. Furthermore, the systematicapproach adopted in this book gains patientgratitude and creates clinical satisfaction.

I am indebted to Ronald Goldstein, who isundoubtedly regarded as the pioneer of aestheticdentistry. The two people who have spurred meon: Bernard Touati and Nitzan Bichacho, as wellas eminent clinicians who have helped, directlyor indirectly, with this project, including AvishaiSadan, Gerard Chiche, Markus Blatz, TomTrinkner, William Liebenberg, Alan Gluskin,Homa Zadeh, Fereidoun Daftary, StefanoGracis, Mauro Fradeani, Douglas Terry, StephenHancocks, Rafi Romano, Galip Gürel, Alan Sidi,Eric van Doreen, Youval Elyat, Ervin Weiss,Nitzan Fuhrer, Ilan Gilboa, members of the European Academy of Esthetic Dentistry andDentology study group, especially Sanjay Sethi,who founded Dentology five years ago for like-minded clinicians.

xii Preface

My special thanks to Stephen Chu for hissupport and friendship, and whose bestsellingbook on colour has been the inspiration forChapter 4 of this book. I would also like toexpress my gratitude to the ceramists whosetalents are featured through this publication,including Willi Geller (Maestro), Gerald Ubassy, Jason Kim, Paul Sturridge, Jean MarcEtienne, John Hubbard and David Korson. Mydear friends Karl Theis, Magnus Persson, Ann-Louise Holding, Hina Halai, Sital Patel, BobMuggleston, my father, Mansur Ahmad, late

mother Bilqis Bibi, aunty Razia Khanum andsisters Ayesha and Samina. I am also thankful toOmowunmi Braithwaite for her kindness andcompassion, and for being there when my wifeand I most needed her.

Finally, I am grateful to Caroline Connelly andall the staff at Blackwell Publishing for their hardwork and efficiency in making this project areality.

Irfan Ahamd

Treatment planning involves applying learneddidactic scientific knowledge to clinical realities.To achieve this goal, a systematic approach isnecessary, using the acronym APT (assessment,planning and treatment) (Fig. 1.1). Aesthetictreatment, unlike other forms of dental care,requires a radically different approach. Forexample, the protocol for endodontic treatmentis infection removal and subsequent sealing ofthe canal(s), requiring little or no input from thepatient. In fact, the patient is usually oblivious tothe treatment modality, and is only aware of res-olution of symptoms. Aesthetic treatment on theother hand, is highly subjective, with activepatient participation. The colour, form and characterisation of anterior aesthetic restorationsare open to scrutiny by the patient, family andfriends. The clinician therefore has to adopt a different protocol to meet these challenges for avoiding disagreements and unsatisfactoryoutcomes.

In order to execute aesthetic treatment suc-cessfully, the following items are prerequisite:

� Time� Aptitude� Knowledge� Skills

� Experience� Patience

Without these qualities, aesthetic treatment is neither possible nor successful. To achievethese objectives, use of a systematic approach,such as APT, maximises success and minimisesfailures.

Assessment

Assessment begins with an initial consultation,which is a mutual evaluation between the patientand clinician. This appointment generates rev-enues below the clinician’s usual hourly rate, but is worthwhile in the long run. The initialencounter is predominantly psychological, theclinician determining the patient’s persona, emo-tional make-up and needs, and the patient assess-ing his/her confidence of the dental team, as wellas the ambience of the dental practice. The clin-ician’s approach should be empathetic andsincere, rather than dismissive and authoritarian,since this meeting will determine whether a sat-isfying dentist–patient relationship is possible.1

Because aesthetic treatment is protracted, often

1Treatment planning – assessment,planning and treatment

2 Protocols for Predictable Aesthetic Dental Restorations

involving a multiphase treatment plan, mutualrespect should be established and maintainedthroughout the entire period. If mutual respectand rapport are not forthcoming, therapy is des-tined to failure, irrespective of clinical skill andsupport of the dental team.

The subsequent appointment is much longer,involving information gathering using a varietyof examinations. More than one appointmentmay be necessary to gather information, re-quiring referral to a hospital or specialist clinicsfor specific diagnostic tests. The information-gathering process is divided into histories, exam-ination and technological tests. Of course, notevery item is necessary for every patient, depend-ing on prevailing symptoms. Below is a proposedlist, together with salient points for each item.

(1) Histories:� Medical history – diabetes, immune

response compromises, medication� Risk history – medical (xerostomia, dia-

betes, immunosuppression), genetic(periodontal disease and caries), com-munity (cultural, lifestyle priorities), fluoride (demographic), status (socio-economic, education), environmental(occupational hazards), disabilities(Down’s syndrome, epilepsy), habits(smoking, betel nut chewing, poorplaque control)

� Nutritional history – diet, gastric regur-gitation, bulimia

� Dental history – attendance, previoustreatment, records from former or refer-ring dentist, phobias, dental priorities,oral hygiene

(2) Examination:� Verbal – initial consultation (listening

and evaluation to determine patient’schief complaint as well as gaugingpersona, expectations and wishes)

� Visual: � Extra-oral: facial symmetry, facial

contours, labial grooves and fis-sures, skeletal profile, muscularspasms, lymph nodes, speech

� Aesthetic: smile line, degree of gingival exposure during a smile,degree of tooth exposure at rest andduring a smile, tooth form, colourand texture

� Intra-oral: soft tissue lesions.Tongue size and breathing patterndue to enlarged tonsils causing pharyngeal airway obstruction andtongue thrust may compromiseanterior restorations. Caries, peri-odontal biotypes and bioforms,width of attached gingiva, edentu-lous ridge configuration according to the Misch classification2, dentalarch shape (anterior–posterior andlateral), imbrications and spacing,interocclusal clearance (checking for over-eruption, displacement ofcondyles, alveolar bone loss due to previous extractions, tooth wear(erosion, attrition, abrasion, abfraction), fractured teeth usingtransillumination

� Occlusal assessment: centric occlu-sion (CO), centric relation (CR),lateral guidance, anterior guidance,horizontal and vertical overbite,Curve of Spee and Wilson, eccentriccontacts, bruxism, failed restorations

� Tactile – muscle palpation, temporo-mandibular joint (TMJ), fremitus, toothpercussion (endodontic evaluation)

� Written – document verbal and visualfinding. Use questionnaire(s) for ascer-taining patient’s aesthetic expectations.These forms should enquire about whichaspect of aesthetic treatment is impor-tant to the patient, e.g. colour, shape,alignment of the teeth, etc.

Planning

TreatmentAssessment

Systematicapproach

Figure 1.1 The APT (assessment, planning, treatment) modelfor a systematic approach to treatment planning.

Treatment planning – assessment planning and treatment 3

(3) Technological tests:� Articulated study models with jaw rela-

tion records� Articulators and jaw movement/registra-

tion analysers� Diagnostic wax-ups (Figs. 1.2 & 1.3)� Radiographs (current and from previous

or referring dentist)� Photographic documentation (intra-oral

and 35 mm cameras)� Scans: computerised tomography (CT)

scan, linear tomography, or interactiveCT for assessing adequate bucco-lingualwidth and length of alveolar ridge forimplant placement (Figs. 1.4 & 1.5); andmagnetic resonance image (MRI) forsuspected TMJ arthropathy

� Shade analysis: visual, digital, visit toceramist (see Chapter 4)

� Instrumental/chemical caries and peri-odontal detection

� Pulp vitality tests (thermal and electrical)� Bacterial and biopsy tests

Planning

Having completed the initial consultation, nec-essary histories, examinations and tests, the nextstage is planning. The planning phase involvesdiagnosis, risk assessment, evidence-based deci-sion making and presenting treatment proposalsto the patient.

Diagnosis

Before a diagnosis can be established, the clini-cian has to integrate all the pieces of informationin a coherent and logical manner, not unlike ajigsaw puzzle, creating a picture of the patient’smedical and dental status. Depending on the clinician’s experience, relevant data is high-lighted, while less important information is rele-gated, allowing commencement of the diagnosticprocess.

Diagnosis is the premise of planning, preced-ing any prescribed treatment. It is not limitedmerely to current symptomatic signs, but incor-porates aetiology of the prevailing pathology.

A definitive diagnosis is essential before com-mencing therapy. For example, repairing a fractured tooth or crown with a replacementrestoration is insufficient. The underlying causeof why the tooth or crown fractured is essentialif the repair is to be successful (Fig. 1.6). Factorssuch as occlusal abnormalities, periodontaldisease, endodontic status, etc. require investiga-tion so that aetiology is defined and treated,before repair is instigated.3

Risk assessment

Currently, most risk assessment by clinicians ishighly subjective, leading to inconsistencies and

Figure 1.2 Pre-operative study casts showing reduced verti-cal dimension.

Figure 1.3 Diagnostic wax-up for proposed increase inocclusal vertical dimension for patient in Figure 1.2 (labora-tory work by Gerald Ubassy, France).


inaccuracies. This usually results in underesti-mating disease severity, and necessitates morecomplex and costly treatment later. The aim ofrisk assessment is to tailor treatment plans individually according to a patient’s dentalprofile, thereby moving away from a ‘repairmodel’ to a ‘wellness model’. This will discour-age disease recurrence and encourage long-termoral health.

Many studies have cited that the two majordental diseases, caries and periodontal disease,are preventable. This assertion is based on iden-tifying and reducing risk, and implementingappropriate preventive measures.4 For example,the diagnosis of severe periodontal disease doesnot imply a high risk of periodontal disease.Diagnosis assesses current clinical findings, whilerisk assesses or predicts future disease patterns.

This is because traditional diagnosis is two-dimensional (2D) (clinical examination and radi-ographs), which indicate disease severity. Thethird dimension, risk assessment, is omitted. Athree-dimensional (3D) diagnosis for periodontaldisease incorporates the following (Fig. 1.7):

� Clinical examination and findings� Radiographic assessment� Risk prediction

Using a 2D diagnosis, all patients will be pre-scribed the same treatment, irrespective of risk.However, when individual patient risks areincorporated in a 3D diagnosis, the treatmentplan differs for each patient, even though the 2Ddiagnosis is identical. Periodontal risk factors arecrucial when considering implants or aestheticprostheses. For low-risk patients, simple

Figure 1.4 CT scan showing insufficient bone for endosseous implant placement (image courtesy of Dr Alan Sidi, UK).


Figure 1.5 CT scan showing adequate bone for endosseous implant placement (image courtesy of Dr Alan Sidi, UK).

Figure 1.6 De-lamination of veneering porcelain on ametal–ceramic crown.

Risk predication

3Ddiagnosis

Radiographicexam

Clinicalexam

Figure 1.7 The three-dimensional diagnosis model.


prophylactic procedures are sufficient, and theprobability of success of aesthetic restorations or implants is high. This is not the case withmoderate- to high-risk periodontal patients, whorequire extensive periodontal therapy and morefrequent recalls ensuring that periodontal healthis established and maintained. In the latter,patients should be informed that unless theirperiodontal status is maintained, aestheticrestorations or implant longevity may be severelycompromised.

The next question is how predictably andaccurately to assess risk. A recent study showsthat only 20% agreement was evident amongexpert clinicians, indicating that inter-evaluatorassessment is unreliable. The clinical significanceis that either over or under-treatment is pre-scribed depending on the opinion of the exam-iner.5 A quantitative analysis using the PreviserRisk Calculator has been proposed, which accu-rately predicts risk of periodontal disease, froma scale of 1 (low risk) to 5 (high risk). This testuses the latest computer technology and has beenclinically evaluated over a 15-year period. Aswell as assessing risk, the test also provides arating for current disease status from 1 (peri-odontal health) to 100 (severe generalised peri-odontitis). 6 This objective evaluation is a steptowards the clinician being able to modify treat-ment according to risk, achieve and maintainperiodontal health, and prevent future complexand costly therapies. This quantitative analysis isa paradigm shift from a repair to a wellnessmodel.

Evidence-based decision making and treatment

Historically, dentistry was far ahead of medicinewith regard to implementing preventive meas-ures for caries and periodontal disease. Theseprophylactic interventions were underpinned bynearly four decades of scientific research andclinical trials. However, today the profession isso enamoured with technology that it has shedthe solid scientific platform in favour of spuriousmarketing claims. Inventive materials anddevices are readily embraced, endorsed by

charismatic lecturers, and used on patientswithout evidence of long-term clinical success.Many ‘opinion leaders’ that lecture frequently atdental symposia reiterate a particular point ofview, which may or may not be evidence-based. An opinion that is repeated perpetuallyeventually becomes the truth, irrespective of itsvalidity.

There is nothing wrong with this approach aslong as delegates are informed beforehand thatthe speakers are expressing their empirical expe-rience, not scientifically proven rules and guide-lines. As stated below, clinical experience formsa part of an evidence-based approach. Added to this are peer and media pressure, castigat-ing those who prefer the traditional scientificapproach as archaic or old-fashioned. However,sometimes faith is not enough, and seeing orreading anecdotal case studies are insufficient forsound clinical decision making.7

Viewed from a manufacturer’s perspective,dental companies are keen to introduce novelproducts and make profits, which indirectly filter back to the profession in sponsorship foreducational symposia. Furthermore, research isonerous, expensive and protracted, and by thetime the results are published, the product may be obsolete, often replaced by a newerversion. This vicious cycle is then repeated andperpetuated.

The scientific approach, although utopian,hampers innovation and technological advance-ment. Many new technologies have faced problems before a reliable product eventuallyemerges. Ultimately, it is the dentist, not themanufacturer, who is responsible for clinicaldecision making that impacts on patients’ treat-ment. If things go wrong, the patient is unlikelyto blame the manufacturer for the failure. There-fore, the onus is on the dentist to choose ap-propriate materials, backed by evidence-basedresearch, to avoid rebuke or professional negli-gence litigation in the event of failure. Evidence-based treatment8 is succinctly summarised as acombination of (Fig. 1.8):

� Clinical erudition� Sound scientific research� Patients’ needs and wants


Performing successful treatment is a combina-tion of evidence-based information, clinicaljudgement and personal experience. It is thiscombination, rather than just one factor, whichensures validity and successful outcomes. Eachfactor requires scrutiny. Evidence-based infor-mation relies on randomised clinical trials as thegold standard, not merely a single anecdotal casestudy relying on chance events. Clinical judge-ment relies on reading appropriate literature andattending reputable symposia. Finally, personalexperience, although invaluable, should notshroud or bias decision making. What works forone patient, is not a universal therapy for everypatient.

Choosing the most appropriate treatment fora given clinical finding is influenced by the threecomponents of evidence-based therapy: clinicalerudition, sound scientific research and patients’needs and wants. For any given predicament,there are many solutions that yield the desiredresult. However, each modality should be as-sessed according to risks and, eventually, bene-fits.9 For example, an accidental fracture of themaxillary incisor has the following treatmentoptions (Fig. 1.9):

(1) Restore with a direct composite filling:� Benefits – minimally invasive, immedi-

ate, economical

� Risks – technique-sensitive bonding pro-cedures, future staining of composite,microleakage leading to endodonticinvolvement and compromised aesthet-ics, requiring replacement fillings andpossible root canal therapy (RCT)

(2) Restore with indirect ceramic prosthesis(veneer or full coverage crown):� Benefits – excellent aesthetics using an

all-ceramic restoration� Risks – highly destructive, technique-

sensitive procedures, possible endodon-tic involvement due to tooth preparationtrauma, use of a skilled (and thereforecostly) ceramist to match a single crownwith adjacent teeth, protracted, expen-sive, porcelain fracture due to improperclinical or laboratory protocols

(3) Extraction and immediate replacement withendosseous implant and implant supportedcrown:� Benefits – immediate, avoids future

endodontic complications� Risks – surgical involvement, possible

unpredictable soft and hard tissuehealing with compromised aesthetics,use of a skilled (and therefore costly)ceramist to match a single crown withadjacent teeth, protracted, expensive

Patients’ needs and wants

Clinicalerudition

EBtreatment

Scientificresearch

Figure 1.8 Components of evidence-based (EB) treatment. Figure 1.9 External trauma resulting in a fractured rightmaxillary lateral incisor.


Another example is a fractured crown at thecervical margin, on a root-filled premolar withperiapical radiolucency but no active suppura-tion (Figs. 1.10 & 1.11). The treatment optionsare:

(1) Re-RCT with intra-radicular support andreplacement crown:� Benefits – established clinical protocols

for treatment modalities� Risks – further trauma from re-RCT and

post placement to an already weakening,delicate root, relapse of re-RCT, com-promised retention for definitive crownand protracted treatment plan

(2) Apicectomy with intra-radicular support andreplacement crown:� Benefits – retrograde filling without

inflicting trauma to delicate root fromre-RCT

� Risks – shortening of root, resulting inpoor root-to-crown ratio, compromisedretention for definitive crown and pro-tracted treatment plan

(3) Crown lengthening or orthodontic extrusionto increase retention and resistance form fordefinitive crown in conjunction with options(1) or (2):� Benefits – exposure of root surface for

definitive crown margin placement� Risks – shortening of root, resulting in

poor root-to-crown ratio and protractedtreatment plan

(4) Extraction and immediate replacement withendosseous implant and implant supportedcrown:� Benefits – expedient, predictable, but

requires surgical experience and expertise

� Risks – surgical involvement. Localanatomy must be suitable with sufficientquality and quantity of soft and hardtissue volume for success

The patient opted for the last proposal. Firstly,the costs of all the options were similar. Secondly,the bone and soft tissue anatomy were conducivefor successful immediate implant placement with immediate temporarisation, including suffi-cient bone apical to root apex primarily for sta-bility, adequate mesial-distal implant-to-toothdistance of 1.5mm and occlusal clearance (Figs.1.12–1.16).

Arriving at the most appropriate treatmentplan involves clinical findings and a definitivediagnosis, risk assessment, followed by an evidence-based approach (clinical erudition,sound scientific research and patients’ needs andwants). Using evidence-based decision makingand treatment planning maintains professionalcompetence and competitiveness for deliveringhigh quality, predictable treatment. When usingan evidence-based approach, it is important toappreciate that this principle is not dogmatic but

Figure 1.10 Fractured crown on root-filled second premolar.

Figure 1.11 Radiograph of tooth in Figure 1.10 showing athin root cross section and periapical radiolucency.


pragmatic, incorporating clinical experience aswell as respecting patients’ preferences anddesires.10

Presenting treatment plan proposals tothe patient

A treatment plan is a proposal, not a militaryprocedure. In fact, treatment can change due toa myriad of reasons, including the patient’sambivalence, prevailing clinical presentations,unforeseen complications, financial burdens, etc.At the onset, it is the clinician’s duty to conveythe flexibility and fluidity of the proposed treatment, indicating that as treatment

Figure 1.12 Immediate placement of implant fixture(Replace Select, Nobel Biocare) following atraumatic extraction.

Figure 1.13 Abutment with occlusal plug prior to immedi-ate provisionalisation.

Figure 1.14 Four-month radiograph showing osseointegration.

Figure 1.15 Impression with implant analogue for fabrica-tion of definitive crown.

Figure 1.16 Cemented implant-supported all-ceramiccrown (compare with Figure 1.10).


progresses, changes or alterations may be desir-able or mandatory.

The presentation should encompass simpleand clear verbal and written communication.Visual aids, such as radiographs, scans, studymodels and pictures, add credence to the writtenand spoken word. When starting a new aestheticpractice, it is often difficult to show treatmentcarried out by the clinician, and using informa-tion leaflets and dental journals is extremelyhelpful. However, over time, it is invaluable tobuild up a portfolio, especially for sceptics, whomay question competence of the operator. Fur-thermore, showing one’s own work furtherenhances confidence and convinces patients thatwhat is proposed has been previously achievedby the treating dentist.

Many patients are oblivious of diseaseprocesses in their mouth, and visual aids areinvaluable for raising awareness of potential orcurrent problems (Fig. 1.17). Numerous visualaids are available, ranging from a face mirror to the latest computer software. For aesthetictreatment, intra- and extra-oral cameras arecrucial at every stage of therapy, starting withpre-operative status, aesthetic analysis, shadeanalysis, potential complications, patient accept-ance of aesthetics and post-operative results.11 Aswell as a presentation tool, high-quality imageryis important for patient–dentist–specialist–ceramist communication and medico-legal docu-mentation, especially if treatment does not

proceed as anticipated. A checklist of itemsrequired, together with their diagnostic value isas follows:

� Extra- and intra-oral photographs – aes-thetic and shade analysis, pathology anddefective existing restorations

� Computer-generated simulations showingproposed treatment possibilities. Althoughuseful, this form of simulation is potentiallyproblematic since the simulation may not beclinically feasible. It is probably wiser to usea wax-up, a ‘real’ as opposed to a ‘virtual’3D object which can show the possibilitiesof a specific option

� Radiographs – infection, caries, defectivemargins, root fillings, bone loss, vital structures

� Scans showing bone quality and quantity ifimplants are considered

� Mounted study casts – occlusal assessment� Diagnostic wax-up – intended design of the

restorations (Figs. 1.18 & 1.19)� Results of any bacteriological tests – modify

periodontal therapy� Technologically based caries and periodon-

tal tests – verify clinical findings� Practice internet web site – useful for

showing patients the practice profile, and thetype of work achievable by the treating clinician

Having gathered the visual aids, the next stageis conveying these to the patient in a logical and

Figure 1.17 The patient was unaware of the defective ante-rior maxillary restorations, which are a potential site for afuture disease process.

Figure 1.18 Severe misalignment of maxillary anteriorsextant.


organised manner. Communication is bothverbal and written. Verbal communicationshould take place in a serene, unfettered, relaxed,unrushed ambience. The choice of words shouldbe non-technical, non-emotive and non-phobic.12

For example, describing intricate details of anapicectomy, including suppuration and haemor-rhage details, is likely to alienate patients. Con-versely, describing an apicectomy as removingbacteria, improving function and appearance ismore palatable. Cautionary discretion is requiredregarding the current craze for cosmetic ‘extrememakeovers’. These trends are predominatelymedia propagated, often prejudicing the laymaninto the belief that cosmetic wonders can fulfiland enrich their lives. These views are rapidlyentering dentistry, with the result that treatmentis often patient driven. There is also an emergingbreed of clinicians prejudging patients’ desiresand influencing their decisions in favour of thesemakeovers. Unfortunately, the motive behindthis influencing is purely fiscal, where marketingtakes precedence over ethics and clinical neces-sity. Furthermore, dentistry is not the fashionindustry. It is very easy to throw away a garmentonce its haute couture appeal has elapsed, whichis not the case for ‘cosmetic restorations’ createdby irreversible destruction of natural teeth. The morality of this dilemma resides with the clinician.

Ultimately, the written word forms a contractbetween the dentist and patient. Once again, the

wording should be non-technical, outlining thepresent clinical situation, treatment options with benefits and risks of each procedure (withscientifically based prognosis for a specific treat-ment option), expected time scale, costs,methods of payments and practice polices (e.g.failed appointments), and guarantees. The treat-ment plan should also incorporate informedconsent. Informed consent, as required by mostUS states, has the following six elements:13

� Correct diagnosis of symptoms and findings� Nature and purpose of proposed treatment� Risks of treatment� Likelihood of success� Alternative options� Prognosis

Treatment

The last part of APT is treatment. Treatment isinfluenced by biological, clinical, psychosocialand economic factors.14 The biological factorsinclude systemic and nutritional health, as wellas local factors, such as periodontal biotype.Clinical aspects include knowledge, techniquesand manual dexterity of the operator, while economic constraints determine the degree ofsophistication of the proposed treatment. Asstated above, an evidence-based approach isproactive intervention, promoting oral health,reducing tooth loss and minimising the need forfuture complex therapy.15

As well as using an evidence-based approach,aesthetic treatment also relies on the clinician’sand ceramist’s artistic flare. At the outset, the operator should exercise clinical self-deprecation, stepping back and asking whetherhe or she possesses the technical competence,experience, psychological knowledge and artisticability to perform aesthetic treatment. One mustappreciate individual limitations, professionalresponsibilities, effective communication and acollaborative effort when delivering quality care.Furthermore, aesthetic treatment is not the remitof every dental practice. Some practices provideroutine, stereotypical, run-of-the mill treatment.

Figure 1.19 Diagnostic wax-up showing proposed appear-ance for maxillary incisors and canines for patient in Figure1.18 (laboratory work by Jason Kim, New York).


If this is the case, then referral to a specialist isprudent; the specialist should have an individual,‘more than just a restoration’ approach. As aconcluding comment: perfection takes time andexperience, but optimal dentistry is, and shouldbe, a tangible goal for every practice.16

Once a treatment plan is accepted, the stagesof execution can be considered. Most aesthetictreatment plans are multiphase and multidisci-plinary. The following is a summary of the chronological stages. Every stage may not beapplicable for every patient, but is listed for thesake of completion. When moving from one stageto the next, it is important to remember thattherapy should follow the health, function andaesthetics (HFA) triad discussed in Chapter 2.

(1) Alleviate pain and stabilise active disease(2) Restore oral health by prophylactic measures(3) Perform APT (assessment, planning,

treatment)(4) Ensure medical diseases are controlled or

under supervision(5) Liaise with specialist(s) for advice or treat-

ment of skeletal, orthodontic, mucogingivalor osseous anomalies

(6) Liaise with ceramist regarding shade analy-sis and feasibility of proposed aesthetic treatment

(7) Commence treatment

Clinical case study

The clinical case study below illustrates a sys-tematic approach to treatment using APT.

Assessment

Initial consultation

The patient was referred by an implantologist forimprovement of anterior aesthetics. The lady was40 years old, intelligent, elegant, sophisticatedand affable. She was distraught and very con-cerned about her dentition, recalled previousunpleasant dental experiences and failures andwas sceptical about future treatment.

Histories

� Medical history – no systemic illness or medication

� Risk history – no genetic predisposition toperiodontal disease, high socio-economicstatus, no occupational hazards, non-smoker, regular exercise, health conscious

� Nutritional history – healthy diet� Dental history – regular attendance, visits

to hygienist, poor-quality previous dental treatment, no records available from formerdentist

Examination

� Chief complaint – improve anterior dentalaesthetics

� Visual – no lymph swellings, low lip line(upper lip concealed maxillary incisors – Fig. 1.20)

� Intra-oral – no soft or hard tissue pathology.Retained deciduous canines, congenitallymissing maxillary lateral incisors, withmesial drifting of the canines distal to thecentral incisors

� Triangular-shaped, chipped maxillary cen-trals lacking dominance due to the widepseudo-lateral incisors. Thin scalloped peri-odontal biotype. Defective and chippedporcelain laminate veneers on the secondarycanines (to simulate the missing laterals) anddeciduous canines (to simulate secondarycanines). Plaque and calculus build-up, staining and discolouration of anterior teeth.Gingival zeniths of pseudo-lateral incisorsapical to central incisors (Figs. 1.21–1.23)

� Occlusion – steep anterior guidance, result-ing in fractured laminates on secondarycanines. Right and left group function, noeccentric working or non-working contacts,and absence of parafunctional activity

� Tactile – no muscular spasm or TMJ dysfunction

� Written – aesthetic evaluation questionnairerevealed that patient was enthusiastic aboutrestoring her smile, but cynical due to previ-ous poor-quality treatment


Technological

� Radiographs – periapicals showed completeroot absorption of retained deciduous canineand local inflammation necessitating imme-diate extraction (Figs. 1.24 & 1.25).

� Upper and lower pre-operative impressionwith facebow and jaw registrations formounting on semi-adjustable articulator fordetailed occlusal assessment

� Diagnostic wax-up to assess feasibility oftreatment options for improving anterioraesthetics (Figs. 1.26 & 1.27)

� Photographic – facial, dentofacial anddetailed dental images with 35 mm camera

� Scans – none� Shade analysis – using two shade guides,

Vita Classic and Vita 3D (Figs. 1.28 & 1.29)� Pulp vitality – all anterior teeth vital, with no

periapical lesions� Bacterial and biopsy tests – none

Planning

Diagnosis

Poor-quality dental restorations, poor anterioraesthetics, calculus and plaque deposits, staining,fractured and defective laminates on pseudo-laterals, chipped incisal edges on central incisors.Resorbed and deficient (bucco-palatal) alveolarridge at extracted deciduous canine sites.

Figure 1.20 Low maxillary lip line concealing cervicalmargins of maxillary anterior teeth.

Figure 1.21 Pre-operative status in centric occlusion (seetext for details).

Figure 1.22 Pre-operative status in anterior protrusiveexcursion (see text for details).

Figure 1.23 Pre-operative status: occlusal view (see text fordetails).


Figure 1.24 Extraction of retained deciduous canines (facialview).

Figure 1.25 Extraction of retained deciduous canines(occlusal view).

Figure 1.26 Pre-operative study cast.

Figure 1.27 Diagnostic wax-up for anterior maxillarysextant.

Figure 1.28 Shade analysis using the Vital Classic shadeguide.

Figure 1.29 Shade analysis using the Vita 3D shade guide.


Mesial-distal space between pseudo-laterals andfirst premolar = 4mm on each side of the arch,insufficient for implant placement. A minimumof 1.5mm implant-to-tooth distance required,and even using a small platform fixture (3.5mm),the prevailing 4mm space is inadequate.

Treatment objectives

� Maintainance of existing occlusal scheme� Dominance of maxillary centrals� Narrower maxillary pseudo-laterals� Resolving apically located gingival zeniths of

pseudo-laterals� Replacement of missing canines� Improvement of colour of mandibular teeth

Risk assessment

Low risk of periodontal disease due to shallowpockets, no systemic illness, no genetic predis-position to periodontitis, regular dental atten-dance, healthy diet. However, the thin scal-loped periodontal biotype necessitates care withrestorative or surgical procedures to prevent gin-gival recession.

Evidence-based decision making and treatment

The treatment options presented to the patientwere as follows:

(1) Removable upper denture� Benefits – expedient, non-invasive,

economical� Risks – anti-social, onerous, food trap-

ping, temporary solution, future replace-ment dentures, accelerated wear andstaining of acrylic artificial teeth

(2) Bleaching mandibular teeth� Benefits – predictable, immediate gratifi-

cation, economical� Risks – sensitivity, may require repeated

application(s) to achieve desired result(3) Orthodontics to increase space between

pseudo-laterals and first premolar to allowendosseous fixtures (with bone grafting) andeventual implant-supported crowns. Theapically located gingival zenith on the

pseudo-laterals could also be rectified byorthodontic extrusion or soft tissue grafts� Benefits – refined, complicated, state-of-

the-art treatment, minimally invasive� Risks – protracted, bone or root absorp-

tion due to orthodontic movement,orthodontic retainers, surgical complica-tions, such as infection, bone loss andunpredictable soft tissue contours, costly

(4) The prosthodontic solution consisting ofporcelain laminate veneers (PLVs) on thecentrals, with a fixed partial denture (eithertwo distal cantilevers from the pseudo-laterals, or two three-unit bridges frompseudo-laterals to first premolars)� Benefits – excellent aesthetics, expedient,

predictable� Risks – highly invasive, technique-

sensitive, possible future endodonticinvolvement of prepared teeth, costly

In isolation, none of the above options resolvesall the treatment objectives. In order to arrive ata definitive treatment plan, more than one of theabove options is necessary. After consideringthese four options, the patient opted for option(2) (bleaching) with option (4) (prosthodonticsolution). Using an evidence-based approach, thefollowing require consideration:

� Clinical erudition – knowledge, skill andexperience. It was decided to adhere to theexisting occlusal scheme, group function onboth sides. Additionally, PLVs were choseninstead of full coverage crowns because ofthe steep anterior guidance, and a protrusiveslide on natural tooth surfaces would ensurebetter long-term function

� Sound scientific research – bleaching is a pre-dictable modality if judicially applied. PLVsare also predictable using an adhesive pro-tocol for cementation. In order to maximiseaesthetics, an all-ceramic alumina bridge wasselected (In-Ceram, Vita), which has a rea-sonable short- to medium-term success ratefor anterior regions of the mouth (seeChapter 3)

� Patient’s needs and wants – the treatmentplan was finalised once the patient expressedher wishes. The lady was totally against sur-


gical intervention and refused protractedtreatment duration due to previous dentalfailures. Since the lip line was low, it wasdecided to accept the apical zeniths of thepseudo-laterals. She was also adamant aboutimproving the tooth colour of her anteriormandibular teeth

Treatment

The treatment sequence is as follows:

(1) Achieve periodontal health and stability byprophylaxis and oral hygiene instructions

(2) Provide bleaching trays and allow 3–4weeks for colour stabilisation before finalshade determination

(3) Liaise with ceramist for detailed shade andaesthetic analysis using wax-up, photo-graphs and discussions with patient

(4) Tooth preparations for PLVs on centralincisors, and two fixed partial denturesfrom pseudo-laterals to first premolars. Usetemporary restorations to assess health,form, occlusion, phonetics and creatingovate pontic sites for missing canines (Figs.1.30–1.32)

(5) Verify shade after tooth preparation, espe-cially for PLV on central incisors (Fig. 1.33)

(6) Once gingival margins are healthy andstable, make final impressions withfacebow and jaw registrations (Fig. 1.34)

(7) In the dental laboratory, pour two plastermodels; leave one untrimmed to confirmemergence profile and cervical contours; thesecond trimmed dies are mounted on anarticulator for fabrication of the definitiveprostheses (Figs.1.35 & 1.36)

(8) Try-in restorations, check fit, occlusion,phonetics and aesthetics (Figs. 1.37 &1.38). In this instance the following anom-alies were apparent (Fig. 1.39):(i) Incorrect axial inclination of the right

canine pontic and left pseudo-lateral(ii) Marginal discrepancies on mesio-

buccal and palatal aspects of abutment14, and palatal aspects of abutments 22 and 24

(iii) Patient requested removal of interproxi-mal staining between pseudo-lateralsand canines and a reduction in the cer-vical chroma stains

(9) Since the marginal discrepancies of thealumina framework cannot be corrected byadding porcelain, new bridges were fabri-cated. The result is shown in Fig. 1.40, cor-recting the aberrations listed above

(10) The restorations were cemented by using anadhesive technique with a resin luting agent

(11) The post-operative status shows impec-cable periodontal health and aesthetic in-tegration of the PLVs and fixed partialdentures (FPDs) (Figs. 1.41–1.43). Theoriginal treatment objectives are achievedas follows:(i) Maintenance of existing occlusal

scheme(ii) Dominance of maxillary centrals(iii) Narrower maxillary pseudo-laterals(iv) Apically located gingival zeniths of

pseudo-laterals are hidden by the lowlip line

(v) The missing canines have been replaced(vi) Improvement of colour of mandibular

teeth

The treatment plan above has followed threesequential steps, achieving periodontal health,occlusal and phonetic function, and anterior aes-thetics (the HFA triad), which is the theme of thenext chapter.

Figure 1.30 Right lateral view of tooth preparations.


Figure 1.31 Left lateral view of tooth preparations.

Figure 1.32 Occlusal view of tooth preparations.

Figure 1.33 Shade analysis after tooth preparation using theVital Classic shade guide.

Figure 1.34 Definitive maxillary arch impression using anaddition silicone material (Provil Novo, Heraeus Kulzer).

Figure 1.35 Untrimmed master cast.

Figure 1.36 Trimmed model and dies mounted on semi-adjustable articulator.

Figure 1.37 Try-in of definitive restorations (facial view). Figure 1.38 Try-in of definitive restorations (occlusal view).

Correct axialinclination(mesially inclined)

Reduce chroma intensityof cervical staining on both bridges

Incorrect axialinclination(distally inclined) –modify to simulatethat of tooth 12

Marginal discrepancies on mesio-buccal and palatal aspects of abutment 14, and palatal aspects of abutments 22 and 24.

Correct axialinclination(mesially inclined)

Incorrect axialinclination(distally inclined) –modify to simulatethat of tooth 23

Remove interproximal stainingbetween laterals and canines

Figure 1.39 Evaluating aesthetic and technical faults at try-in stage.

Figure 1.40 Post-operative view after correcting faults at try-in stage.

Figure 1.41 Post-operative 1:1 view showing aestheticimprovement, and immaculate integration of laminates andceramic bridges with a healthy surrounding periodontium.


Figure 1.42 Pre-operative lateral dento-facial view.

Figure 1.43 Post-operative lateral dento-facial view.


References

1 Payne, S.H. (1968) Knowledge and skills in thepractice of prosthodontics. J Pros Dent, 20(3),255–257

2 Misch, C.E. (1990) Division of available bonein implant dentistry. Int J Oral Implantol, 7,9–17

3 Glick, M. (2005) Scope of practice: A matterof skills, knowledge and erudition. JADA,136, 430–431

4 Axelsson, P., Lindhe, J. and Nystrom, B.(1991) On the prevention of caries and peri-odontal disease. Results of a 15-year longitu-dinal study in adults. J Clin Periodontol, 18,182–189

5 Persson, G.R., Mancl, L.A., Martin, J. andPage, R.C. Assessing periodontal disease risk:a comparison of clinicians’ assessment versusa computerized tool. JADA, 134, 575–582

6 Page, R.C., Martin, J.A. and Loeb, C.F. (2004)Use of risk assessment in attaining and main-taining oral health. Compendium, 25(9),657–669

7 Robbins, J.W. (1998) Evidence-based den-tistry: What it is, and what does it have to dowith practice? Anecdote vs. data – a case forevidence-based decision making. Quintes-sence Int, 29(12), 796–799

8 Sackett, D.l., Rosenberg, W.M., Gray, J.A.,Haynes, R.B. and Richardson, W.S. (1996)

Evidence based medicine: what it is and whatit isn’t. Br Med J, 312, 71–72

9 McGuire, M.K. and Newman, M.G. (1995)Evidence-based periodontal treatment I. Astrategy for clinical decisions. J PeriodonticsRestorative Dent, 15, 71–83

10 Newman, M.G. (1998) Improved clinicaldecision making using the evidence-basedapproach. JADA, 129, 4–8

11 Ahmad, I. (2004) Digital and ConventionalDental Photography: A Practical ClinicalManual. Quintessence Publishing Co. Inc.,Chicago

12 Bain, C. (2004) Treatment planning in generaldental practice: Case presentation and com-munication with the patient. Dental Update,March, 72–82

13 Mills, E.J. (2002) A clinical method for thediagnosis and treatment planning of restora-tive dental patients. J Oral Implantol, 28(3),122–127

14 Bader, J.D. and Ismail A.I. (1999) A primer onoutcomes in dentistry. J Publ Health Dent, 59,131–135

15 Axelsson, P., Paulander, J., Svardstrom, G.and Kaiser, H. (2000) Effects of populationbased preventive programs on oral health con-ditions. J Parodontol Implantol Orale, 19,255–269

16 Drago, C.J. (1996) Clinical and laboratoryparameters in fixed prosthetic treatment. JProsthet Dent, 76, 233–238

Dental care can be succinctly defined by thehealth, function and aesthetic (HFA) triad. Theprimary aim of any therapy is resolution ofdisease, resulting in a state of well-being. It isimportant to realise the hierarchy of this triad,attainment of health, followed by function, fol-lowed by aesthetics. One can achieve healthwithout function or aesthetics, and both healthand function are possible without aesthetics.However, aesthetics are not possible if the firsttwo, health and function, are absent.

To illustrate this, consider the following examples. A lateral incisor extracted following a hopeless prognosis of periapical infectionachieves health, but not function or aesthetics(Fig. 2.1). Similarly, buccal amalgam fillings inthe mandibular incisors achieve health and func-tion, but are clearly unaesthetic (Fig. 2.2). Con-versely, a beautifully fabricated crown for ananterior tooth without previously resolving periodontal and occlusal problems is prone tofailure. The crown on the left lateral incisor isaesthetically acceptable, but due to poor peri-odontal health or occlusal disharmony, it is nevertheless perceived as unaesthetic (Fig. 2.3).Furthermore, because of these compromises,fracture, de-cementation or periodontal diseasewill ultimately cause failure. In the latter case,

the treatment sequence should start by resolvingperiodontal and occlusal issues (health and function), before fabrication of the definitivecrown.

The clinical sequence of the HFA triad is para-mount for durability, longevity and success of alldental treatment. The discussion below outlinesthe constituents of the HFA triad (Fig. 2.4).

Health

Having treated gross soft and hard tissue pathol-ogy, the next step is achieving health of the den-tition and surrounding periodontium. Attaininghealth of a tooth may involve decay removal,replacing defective fillings, investigatingendodontic lesions or resolving occlusal dys-function with any associated TMJ pathosis. Inconjunction with the latter, a healthy periodon-tium is also essential for ensuring survival of atooth. The rate of soft tissue healing depends onpatient constitution, systemic disease, severity ofthe prevailing lesion and the degree of dentaltrauma during restorative procedures. Thischapter focuses on general periodontal and

2The health, function and aesthetic triad


occlusal aspects, while ensuing chapters detailprotocols for specific lesions.

The periodontium

Before commencing any reparative therapy torestore function and aesthetics, it is essential to achieve healthy tissues in the oral cavity. Only then can reconstruction of diseased anddamaged tooth structure be predictably achievedand maintained.

Anatomy of the periodontium

The periodontium is a combination of hard andsoft tissues. From a superficial aspect, the softtissue covering is divided into the gingiva andalveolar mucosa. The gingiva is masticatorymucosa extending from the free gingival marginand terminating apically at the muco-gingivaljunction to become the alveolar mucosa (Fig.2.5). The gingiva is keratinised and furtherdivided into the free and attached gingiva, whosetexture varies from a highly stippled to a smoothappearance. On occasions, an elevation of thefree gingival margin, termed the gingival groove,is evident (Fig. 2.6). Both free and attached gin-givae show huge variance in the linear dimen-sions (width), thickness (bucco-lingual), texture(degree of stippling) and colour (intensity of pink and/or physiological pigmentation) (Figs.2.7–2.9). The width of the attached gingivaeranges from 0.5–8.0mm, and its thickness fromthe free to attached sections decreases from

Figure 2.1 A missing right lateral incisor shows health, butlacks function and aesthetics.

Figure 2.2 Amalgam fillings in mandibular incisors showhealth and function, but lack aesthetics.

Figure 2.3 The crown on the left lateral incisor is aesthetic,but lacks periodontal health due to marginal inflammation.

Aesthetics

Successfultreatment

Health FunctionFigure 2.4 The HFA triad.

The health, function and aesthetic triad 23

1.56mm to 1.25mm, averaging at 1.41mm. Tra-versing from the anterior to posterior teeth, thewidth decreases, while thickness increases.1

Another correlation is that a wider and thickerattached gingiva is associated with a shallowersulcus depth.2

The function of the attached gingiva, which ismore resilient than the non-keratinised alveolarmucosa, is to withstand normal functional mas-ticatory trauma. When its width is diminishedfollowing surgical or implant procedures, its roleis compromised. The need to have an adequatezone of attached gingiva surrounding implant-supported crowns is contentious (Fig. 2.10).Some authorities advocate that absence of anattached zone has no adverse effects on implantsurvival.3 However, others stress the need for a

Figure 2.5 Superficial anatomy of the periodontium.

Figure 2.6 Elevation of the free gingival margin (FGM) istermed the gingival groove.

Figure 2.7 Smooth attached gingiva.

Figure 2.8 Highly stippled attached gingiva.

Figure 2.9 Melanin-pigmented attached gingiva.


soft tissue zone (minimum 1mm around naturalteeth and 2mm around implants)4 to prevent aninflammatory response. Indeed, it is suggestedthat soft tissue grafts have alleviated persistentinflammation around implants.5 The debate con-tinues, but is seems prudent to have a keratinisedzone around implant-supported prostheses toresist trauma from food impaction and routineoral hygiene procedures, similar to that aroundnatural teeth.

In cross-section, the periodontium is com-posed of three types of tissue; epithelium, con-nective tissue and bone. The free gingival marginforms part of the gingival crevice, which is inter-nally lined by intact, non-keratinised or parak-eratinised epithelium. This sulcus or crevice hasthe tooth surface on one side and the crevicularepithelium on the other. The linear dimension ofthe sulcus varies from 0.26–6.03mm, dependingon numerous factors, including type of tooth, siteof measurement, etc. It is frequently 1mm or less,greater at interproximal than facial sites. Theepithelial attachment (EA) is located below thegingival sulcus and also exhibits variability inlength from 0.32–3.27mm.6 A unique feature of the epithelial attachment is that if severed, by surgical or bacterial trauma, it proliferatesrapidly in an apical direction in approximately 5days.7 The newly formed epithelial attachment is longer, limited only by the connective tissuebelow. However, if inflammatory response of theconnective tissue is also present, this causes lysis

of the connective tissue, which is then no longercapable of acting as a barrier to retard apicalmigration of the epithelial attachment. Thisprocess continues until the epithelial attachmentencounters an intact connective tissue barrier.This is the basic sequence of periodontal pocketformation. It is important to note that the epithe-lial attachment can be located apical to the alve-olar bone crest (ABC) on the cementum of theroot surface. Another significant point is that the EA is longer around teeth with subgingivalrestorative margins compared with non-restoredteeth.

The supracrestal fibres, emanating from theperiodontal ligament, form the connective tissueattachment (CTA) below the epithelial attach-ment. The CTA ranges from 0.29–1.84mm, witha mean of 0.77mm, and is wider on posteriorthan anterior teeth. The connective tissue has theleast variance compared with the sulcus andepithelial dimensions, and 1mm can be safelyused as a clinical guide. The EA + CTA form asoft tissue cuff termed the biologic width (Fig.2.11).

The final component of the dentogingivalcomplex is the alveolar bone housing the tooth,usually located apical to the epithelial and con-nective tissue attachments. The alveolar housingusually follows the contours of the cemento-enamel junction (CEJ), in a parabolic fashion,with peaks and troughs that are exaggerated onanterior, but diminish around posterior teeth.

Figure 2.10 Lack of attached gingiva around a ceramicimplant abutment (laboratory work by Jason Kim, New York).

Sulcus0.69 mm

(0.26-6 mm)

Epithelial attachment0.97 mm

(0.3-3.3 mm)Biologic width

2.04 mm(variable)

CEJ Connective tissue

attachment1.07 mm

(0.29-1.84 mm)

Figure 2.11 The biologic width.


However, following periodontal disease or iatro-genic trauma, the alveolar crest may be locatedcoronal to the epithelial attachment (Fig. 2.12).

Biologic width

The biologic width has many synonyms, includ-ing buffer zone, soft tissue cuff, soft tissuebarrier, soft tissue shield or subcrevicular attach-ment complex. Whilst some terminology may bemore descriptive than others, the most popularterm is biologic width. Ingber coined the term‘biologic width’ in 19778 based on originalresearch by Gargiulo, Wentz and Orban in1961.9 The concept of the biologic width envis-aged by these authors was based on autopsy andhistological findings, with a mean sulcus depthof 0.69mm, a junctional or epithelial attachmentof 0.97mm and a connective tissue attachmentfrom the CEJ to alveolar crest of 1.07mm. Thesum of linear measurements of EA + CTA (2.04mm) is the biologic width (Fig. 2.13). Sinceits introduction, the 2.04mm measurement hasbeen ubiquitously quoted, reported in dentaljournals, and indelibly ingrained in clinicians’psyche. The biologic width is nature’s approachfor protecting the most important part of thedentogingival complex, the periodontal ligament

and alveolar crest. It is in effect a shield whichendures trauma, both mechanical and bacterial,to ensure longevity of a tooth. If this soft tissueshield is inadvertently damaged or violated, itsprotective function is diminished, placing thesurvival of the tooth in jeopardy.

The main significance of the biologic width isits presence around every healthy tooth. Itsintegrity is indicative of gingival health, and is aguide for restorative procedures. It is obviouslyimperative to maintain this zone, and preventimpingement for longevity of not only the tooth,but also a reparative dental restoration. Physio-logically and qualitatively, the biologic width isa valid concept, but much debate has concen-trated on its quantitative values. Therefore, dif-ferential diagnosis of clinical variations of thedentogingival complex is imperative for avoidingpitfalls.

Biologic width – differential diagnosis

Ensuring the integrity of the biologic width is a shared responsibility of the patient (oralhygiene), clinician (operative trauma, marginlocation) and ceramist (precision restorations).The quoted dimension of 2.04mm is an averageideal, not applicable for each site or every tooth.Furthermore, even if violated, a biologic widthre-establishes, although with a reduced dimen-sion. This suggests that the ideal 2mm is not

Sulcus

Longepithelial attachment

Connective tissueattachment

CEJ

Figure 2.12 A long epithelial attachment, apical to the alve-olar bone crest.

Sulcus

FGM

CEJ

ABC

Periodontalligament

EA

CTA

BiologicWidth

Figure 2.13 Landmarks of the dentogingival complex.


essential for gingival health, and the minimumdimension required for health is still unknown.10

It is also relevant to note the relationship ofvarious landmarks: EA, CEJ and ABC. Usually,the EA and CEJ are both coronal to the ABC.

Type of tooth and restored teeth variationsThe biologic width (EA + CTA) dimensions varyaccording to the type of tooth. There is a pro-gressive increase of the biologic width from ante-rior to posterior teeth. The mean dimensions are:

� Anterior teeth 1.75mm� Premolars 1.97mm� Molars 2.08mm (almost the same as the

ubiquitously quoted width of 2.04mm)

All these measurements are average values,indicating that a viable biologic width as smallas 0.59mm can exist around healthy teeth.Another variation is that restored, comparedwith non-restored teeth, have a wider biologicwidth. As stated above, the increase in the bio-logic width around restored teeth is usually dueto a longer EA, while the CTA and sulcus seemsfairly constant for both restored and non-restored teeth. This clinical observation is irre-spective of the type of restoration.11

Population variationsIn 85% of invididuals, the ABC position is in anormal relationship to the CEJ, with a sulcusdepth of 1mm. However, in 13% of the popula-tion, both ABC and EA are more apical, in a relative normal relationship, but with a longepithelial attachment (and if violated, results ingingival recession and forming of the so-called‘black triangles’). Finally in 2% of the popula-tion, both ABC and EA are more coronal, in arelative normal relationship, but with a smallerEA and a minimal or non-existent crevice. Inthese circumstances, subgingival crown marginlocation should be avoided, as it will almost cer-tainly violate the biologic width.

Apical location of epithelial attachmentAnother situation is when the EA is locatedapical to the ABC. This is a sequela of either peri-

odic intervals of periodontitis or surgical inter-vention. After episodes of periodontitis and sub-sequent pseudo-healing, the apical proliferationof a long healthy EA occurs before connectivetissue formation. Similarly, following surgicalcurettage, without bone grafting or membranebarriers, the epithelium may migrate apicallybefore the connective tissue or bone has had achance to regenerate.

Passive and altered passive eruptionOther factors to consider are passive and alteredpassive eruptions, both of which can be decep-tive when deciding margin location of restora-tions. Passive eruption is evident in elderlypatients where the dentogingival complexmigrates apically, resulting in recession, butmaintaining a normal relationship of the CEJ tothe ABC. Much debate has concentrated onwhether this phenomenon is a physiological orpathological process. The physiological explana-tion is that recession is an ageing process, andthe migration of the dentogingival complex is anormal occurrence. On the other hand, thepathological explanation is that during a life-time, an individual will be inflicted with episodesof acute and chronic gingival inflammation withapical migration of the crestal bone. Whichopinion is correct is irrelevant, but the result isgingival recession.

Altered passive (or delayed) eruption is evidentwhen the epithelial attachment fails to migrateapically, resulting in a long junctional epitheliumwith short clinical crowns, but with a normalrelationship between the CEJ and ABC. Thelatter usually occurs during permanent tootheruption, and, over a period, the EA establishesa normal relationship with the ABC (Fig. 2.14).Failure to diagnose this condition, with inap-propriate crown margin location, may cause gingival recession leading to exposure of crownmargins.

Periodontal bioform and biotypes

Besides biologic width, the other factor to con-sider before considering dental restoration is thepatient’s periodontal bioform and biotype. These


two elements influence treatment modalities, andthe anticipated type of healing response.

The shape of the gingival scallop envelope isdetermined by the position and morphology ofthe teeth. Teeth are categorised into three basicshapes: square, oval and triangular. These threebasic shapes determine the gingival topographyinto thick flat, thin scalloped and pronouncedscallop (Figs. 2.15–2.17).12 The underlying alve-olar bone architecture (distance from interprox-imal crestal peak to mid-facial crestal peak) ofthe three different periodontal bioforms is shownin Table 2.1 below.

The flat type scallop is prevalent in 85% of thepopulation, and the thin type in 15% of cases.

Figure 2.14 Alternated passive eruption on right maxillarylateral.

Figure 2.15 Thick, flat periodontal biotype.

Figure 2.16 Thin, scalloped periodontal biotype.

Figure 2.17 Pronounced, scalloped periodontal biotype.

Table 2.1 Periodontal forms.

Periodontal Mean distance from interproximal form crestal peak to mid-facial

crestal peak (mm)

Flat 2.1Scalloped 2.8Pronounced 4.1

scallop


The flat, thick type is associated with a densefibrotic appearance, and if manipulated or vio-lated by surgical procedures reacts by formingperiodontal pockets. On the other hand, a thinscalloped type has a smooth appearance, withless attached masticatory mucosa, predisposingto dehiscences and fenestrations. Trauma to thistype of periodontium usually results in recession.

The clinical significance of the type of peri-odontium is that violation of the biologic widthin thick types causes pocketing, while in thintypes gingival recession is expected (Figs. 2.18 &2.19). If subgingival crown margins with a thintype violate the biologic width, gingival recessionwill expose the crown–tooth interface and com-promise aesthetics for patients with high lip lines.

This is particularly significant interproximallywhen the distance from the crestal bone tocontact point is 5mm or less, causing incompletepapilla fill of the gingival embrasures (black tri-angles).13 Tooth shape also determines the degreeof interproximal bone between teeth. In a thinscalloped type, the teeth are triangular with nar-rower conical roots, and the interproximal bonevolume is greater (Figs. 2.20 & 2.21). Con-versely, in a thick, flat type, the squarer teethhave wider cylindrical roots, reducing the spaceavailable for the interproximal bone volume. Forthis reason, bone loss in thin, scalloped types isgreater and wider causing pronounced gingivalrecession, compared with the thick, flat types, inwhich bone loss results in pocket formation.

Figure 2.18 Pocket formation with a thick biotype due todefective crowns (note abscess associated with left lateralincisor).

Figure 2.19 Gingival recession around defective crownswith a thin biotype.

Figure 2.20 Triangular teeth have conical roots with greaterinterproximal bone volume.

Figure 2.21 Silhouette of triangular teeth and conical roots,emphasising the increased interproximal bone volume.


Restorative implications

For dental therapy, evaluation of the biologicwidth and periodontal biotype are necessary forthe following treatment modalities:

� Restorative procedures� Surgical crown lengthening� Implants

Restorative procedures

Restorative procedures include fillings and intra-and extra-coronal restorations (direct or indi-rect), which either approach or encroach the dentogingival complex. The biologic width is notclinically visible, and numerous guidelines areproposed to speculate its location and dimen-sions.14 Basically, there are two schools ofthought focusing on definite anatomical refer-ences. The two proposed landmarks are eitherthe ABC, or a healthy and stable free gingivalmargin (FGM).

The rationale for using the ABC is that theaverage dimension of the biologic width is 2mm,verified histologically; this fails to account forclinical variations, however. Many authors andclinicians recommend that restorative marginsand procedures be 2–3mm coronal to the ABCensuring integrity of the biologic width.15 If thismethod is used, differential diagnosis, and indi-vidual variations assessments are essential toavoid entering the EA, or worse, the CTA.

An alternative reference point is a healthyFGM, placing margins 0.5mm apical into thesulcus.16 The rationale for this method is a tan-gible landmark, as opposed to a physiological orhistological reference point of the biologic width.This method obviously avoids encroachment of the biologic width, since the margins willundoubtedly be coronal to the EA. However, thisapproach also has disadvantages. In patientswith a thin biotype or altered passive eruption,gingival recession following restorative proce-dures may expose the crown margin/tooth inter-face, which is significant if the crown cement lineis stained and there is a high lip line. In conclu-sion, both methods offer benefits and limitations,but the key to success is assessing each patient

individually, before choosing the ABC or FGMas a reference point.

Surgical crown lengthening

When therapy involves crown lengthening orimplant placement, assessment of both the bio-logic width and periodontal biotypes is essential.For crown lengthening procedures, a supracre-stal tissue barrier is vital for stability of the FGMand periodontal health.17 For crown lengtheningprocedures, using the FGM as a reference pointis difficult following flap elevation and surgicaltrauma, which distort the pliable soft tissues.Although the average dimension of the biologicwidth of 2mm is not applicable to clinical find-ings around every tooth, it is however, a usefulguide for practical purposes. The variations dis-cussed above can obviously be incorporated intotreatment planning, but for crown lengthening,a minimum distance of 2–3mm is recommendedbetween ABC and the proposed location of theFGM.

Implants

Similar to natural teeth, healthy peri-implanttissues also possess a biologic width. This softtissue cuff is prerequisite for a stable periodon-tal architecture around implant-supported pros-theses.18 For dental implants, both thick, flat orthin, scalloped periodontal biotypes offer advan-tages and disadvantages.

With a thin, scalloped periodontal biotype theinterproximal volume of bone is greater, due tothe narrower conical shape of the roots. This isadvantageous for ensuring the minimum neces-sary implant-to-tooth or implant-to-implant dis-tance, 1.5mm and 3mm, respectively (Fig. 2.22).However, because the gingival tissue is thin anddelicate, inadvertent trauma or incorrect fixtureplacement predisposes to gingival recession(exposing implant–abutment interface), or for-mation of unsightly ‘black triangles’.

For thick, flat biotypes, the roots are broaderand conical, with reduced interproximal bonevolume, leaving less space between adjacent teethor proposed implants. If implants are considered


in these circumstances, the situation can beresolved either by using narrower fixtures withconcurrent mesial-distal bone grafting, or graft-ing on the buccal aspect to compensate for thereduced mesial-distal implant spacing.19 Theadvantage of a thick periodontal biotype is thatdue to the bulky fibrotic attached gingiva, reces-sion is less likely than with a thin, scallopedform.

Finally, margins of any extra-coronal restora-tion (on natural teeth or implant fixtures) shouldmimic the undulations of the CEJ and ACB, withcoronal peaks in the interproximal regions, andapical peaks on facial and lingual aspects. Theintroduction of scalloped (Nobel Perfect, NobelBiocare) and parabolic implants is an endeavourto mimic these natural contours of the CEJ andalveolar crest, with the aim of minimising boneloss in the interproximal regions that oftenoccurs with conventional flat implant plat-forms.20 Using these novel implant designs, theimplantogingival junction simulates a naturaldentogingival junction.

Function

The following discussion about function assumesthat periodontal health is reinstated and main-

tained. The basic premise of function is ensuringcomfort and free range of movement. Functionis divided into two categories: phonetics andocclusion. The former has reasonable concord in the dental literature, but the latter has an aura of mystique and confusion amongst dentalprofessionals.

Occlusion

Occlusion is bewildering for clinicians because ofthe following reasons:

� The thinking about occlusion has undergonedrastic changes in the last century

� Many theories abound, and depending onwhich literature or lecture one cares tofollow, the research is conflicting with variedconclusions

� There is a tendency to overstate and compli-cate this subject, leading to alienation, andspeculation by the recipient audience

In reality, no ideal occlusion exists that isapplicable to every individual. Occlusion, likeother physical features, is genetically determined.Therefore, prescribing a theoretically idealscheme is at best futile, and at worst detrimen-tal. Most dental restorations are carried out witha superficial knowledge of occlusion, but never-theless integrate without due concern with thepatient’s dentition. However, occlusal interfer-ence should not be flippantly introduced, norshould occlusion be regarded as superfluous. Onthe contrary, many failures are avoidable by cor-rectly and carefully addressing occlusal factors.

Ultimately, the practitioner craves for practicalguidance, applicable to the clinical scenario. Thepurpose of this discussion is not to present aca-demic nuances for a scholarly dissertation, but toclarify basic concepts of occlusion that are rele-vant to daily practice.

The first ambiguity is terminology, since manysynonyms are employed.21 For the sake of sim-plicity and clinical relevance, widely acceptednomenclature and definitions are used. These arecentric occlusion (CO), centric relation (CR),working and non-working (contacts and inter-

Figure 2.22 Implant (Replace Select, Nobel Biocare) replac-ing missing left lateral showing 2mm mesial and distal spacebetween adjacent teeth.


ferences), guidance (lateral and anterior) andocclusal vertical dimension (OVD).22

Centric occlusion

CO is defined as maximum intercuspation of themaxillary and mandibular teeth. This is proba-bly the most significant occlusal position, for thefollowing reasons:

� CO is readily reproducible when a patient isasked to close on to the back teeth (Fig. 2.23)

� CO is the ideal position for dissipation ofocclusal forces by the periodontal ligament,since the load is axially directly through theteeth

� CO is a neuromuscular learned behaviourrepresenting the end of the chewing cyclewith maximum force excursion

Consequently, an artificial restoration shouldbe shaped to integrate with CO, which is the casefor the majority of restorations routinely sup-plied by dentists. Assuming that the existingocclusion is asymptomatic, and a limited numberof units are restored (one or two) which do notviolate the existing occlusal equilibrium, CO isprobably the only occlusal position that requiresattention. Specifically, a restoration fabricated inCO, should not create interferences, especially inCR.

Centric relation

CR is the position of mandibular closure whenthe condyles are maximally seated in theirrespective fossae and initial contact is observed

between maxillary and mandibular teeth (Fig.2.24). From this position, there is mandibularprotrusive or lateral excursion into CO. In 90%of the population, CO does not coincide with CR without deleterious effect.23 Hence, pre-treatment occlusal adjustments to achieveharmony with CR and CO are unwarranted andunjustifiable. However, it is necessary to identifyCR, together with the initial antagonist tooth-to-tooth contact, because in certain situations itmay become relevant. This is particularly signif-icant when extensive restorative treatment isenvisaged, for example altering the OVD, or aprofound slide is evident on to anterior teeth thatare being restored, or in the presence of a slidebetween CR and CO with the aim to distalise themandible for creating lingual space for anteriorcrowns. In these cases, the CR is an ideal andreproducible starting point. Finally, when arestoration involves teeth that make the initialcontact in CR, pre-operative identification andocclusal adjustment is beneficial, thus avoidinggrinding the definitive prostheses into occlusion.24

Working and non-working contacts and interferences

Lateral movement of the mandible distinguishestwo sides, termed working side (direction ofmovement) and the contralateral side (awayfrom the movement) or the non-working side.

Figure 2.23 Diagnostic wax-up in centric occlusion (CO).Figure 2.24 Initial tooth contact on first molars in centricrelation (CR).


Contacts can occur on either side guidingmandibular movement, as is the case of balancedarticulation for complete upper and lower den-tures. For dentate patients, balanced articulationis a rarity, since the laterally generated forces,unlike axially directed forces in CO, place unduestress on the teeth. These eccentric occlusalforces, if repeatedly applied for long durations are detrimental to the stomatognathic system,involving teeth, periodontium, muscles of masti-cation and the TMJ. However, neuromuscularadaptation makes these interferences insignifi-cant, and restores physiological function. Apotential problem only emerges when restora-tions are planned which involve these interfer-ences. This applies equally to single as well asmultiple units. When contemplating dental pros-theses that necessitate tooth preparation, inter-ferences are often eliminated, but with resultantreduced inter-occlusal clearance for the proposedrestorative materials. This results in a grosslyoverbuilt prosthesis, preventing mandibularclosure and freedom of movement in lateralexcursions. In these instances, it is prudent toidentify all interferences, and to perform pre-operative judicial adjustments, stabilise theocclusion, and then proceed to the definitiverestoration(s), ensuring that the prepared abut-ments have adequate clearance in CO and lateralexcursions. It is also imperative to avoid intro-ducing new interferences during prosthetic rehabilitation.

Lateral excursions

Mandibular excursions are complicated, but forsimplicity are divided into lateral and anterior.Lateral translation results in guidance of themandible by one or more teeth. In a healthy den-tition, this movement can be canine guided orgroup function (involving more than one tooth,e.g. the premolars), but can also involve incisorsand molars (Figs. 2.25–2.27). Once again, thebiological adaptive capacity allows harmony andclinical intervention is unnecessary. When pros-theses are planned involving guidance teeth, careis crucial. The reason is that the forces placed onthe guidance teeth are lateral, and thereforepotentially more harmful; they may result in

Figure 2.25 Study casts showing group function.

Figure 2.26 Diagnostic wax-up of case study in Figure 2.25,restored to canine guidance.

Figure 2.27 Incisor guidance during mandibular excursions.


fracture or dislodgement of the prostheses ordamage to the stomatognathic system, includingTMJ dysfunction, increased wear, mobility ordrifting of the opposing dentition. Therefore, the proposed prosthesis should emulate thisguidance, and be sufficiently resilient, if nochange to the occlusal scheme is envisaged. Fur-thermore, the prepared teeth should be checkedfor sufficient occlusal clearance in all excursionsto accommodate the proposed metal and/orceramic material.

Another aspect to consider is whether thepatient predominantly masticates in a vertical orhorizontal direction. Vertical biting is preferredsince forces are axial, compared to horizontalchewing patterns with non-axial forces that aredetrimental. In the latter, bruxism is evident with loss of occlusal anatomy. Providing artifi-cial, especially ceramic, restorations should beapproached with caution until diagnosis is con-firmed and grinding stabilised.

If, however, the occlusion requires drasticchange by extensive restorations, a new schemeis planned before treatment commences. Ideally,canine guidance is recommended because itelicits a 30–40% lower muscular activity com-pared to group function.25 However, when acanine is compromised (by periodontal orendodontic involvement), and in order to spreadthe load during lateral movements, changing togroup function may be advisable. This protocolis also prudent if a missing canine is replaced by an implant-supported prosthesis. Becauseimplants lack a periodontal ligament and pro-prioception, it may be prudent to adopt groupfunction, in order to dissipate forces via naturalteeth during lateral excursions.

Anterior guidance

Anterior guidance is the protrusive movement ofthe mandible. When aesthetic restorations areplanned for the anterior mandibular and maxil-lary teeth, anterior guidance is of paramountconcern. Conforming to the existing guidance is relatively simple, but when the occlusion isreorganised, anterior guidance requires re-establishment. A steep guidance causes elevatedmuscular activity, while the opposite is true for

a flatter guidance (Figs. 2.28–2.31).26 Conse-quently, a steep angle may cause cement failure,fracturing of all-ceramic units, tooth mobilityand TMJ pain. A reduced or absent anteriorguidance (incomplete anterior overbite) facili-tates anterior restorations, but complicates pos-terior prostheses since the posterior teeth remainin contact during excursions. The opposite is truefor a steep anterior guidance, which facilitatesposterior prostheses due to canine disclusion, buthampers anterior crowns due to limited spacebetween the maxillary and mandibular anteriorteeth.27

The angle of anterior guidance and directionof the forces also impact on the design of ante-rior restorations. In the natural dentition, even ifthe mandibular teeth contact the palatal aspectof the maxillary teeth at a steep angle, the

Figure 2.28 Steep anterior guidance.

Figure 2.29 Steep anterior guidance.


dentine and enamel dissipate the forces to theperiodontal ligament (Fig. 2.32). However, arti-ficial restorative materials do not possess similarbiomechanical properties to natural dentine andenamel. These inferior substitutes are often inca-pable of performing as well in the oral environ-ment. Ultimately, the weak link yields; this canbe the restorative material (fracture, dislodge-ment), opposing natural teeth (fractures, wear)or soft or hard tissues (periodontal or TMJpathosis). As mentioned above, if an occlusalchange is envisaged (e.g. altering occlusalschemes or increasing the OVD), it is wiser toshape the palatal cingulum of the maxillary teethso that it is flatter and makes perpendicularcontact with the mandibular teeth to directforces axially, placing less stress on the restora-tive material (Fig. 2.33). This procedure of

reducing the anterior guidance from steep toshallow also reduces muscular stress.

The protocol to adopt is determining the startand end points of the anterior slide, and ensur-ing freedom of movement with a shallow anglefor reduced muscular activity.

Occlusal vertical dimension

In order to improve dental aesthetics, the OVDmay need to be increased in certain circum-stances, and therefore warrants special attention.Two aspects require elaboration, the determina-tion and alteration of the OVD.28

Figure 2.31 Shallow anterior guidance.

Figure 2.30 Shallow anterior guidance. Figure 2.32 Mandibular incisor contacting palatal surface ofmaxillary incisor in a non-axial direction.

Figure 2.33 Addition of restorative material to palatalsurface of maxillary incisor to flatten cingulum, and directforces from mandibular incisor in an axial direction.


Proposed methods for determining the existingOVD include nocturnal acrylic splints, neuro-muscular activity, freeway space, positions ofFGMs or CEJs of anterior teeth, facial land-marks, cephalometric analysis and masticatorymuscle lengths. Nearly all these methods arelimited in their conclusions with questionableresults.

Wearing an acrylic splint for ascertainingwhether the proposed increase in vertical heightcan be tolerated is flawed, since any transientpain experienced by the patient usually disap-pears after 1 or 2 weeks, irrespective of thedegree of proposed increase. Due to neuromus-cular reprogramming, any increase in OVD iscompensated for by an adaptive response; there-fore measuring the level of muscle activity or thefreeway space becomes irrelevant.29 Anothermethod is measuring the distance between theFGMs or CEJs of maxillary and mandibularanterior teeth (Fig. 2.34). The important point torealise is that the existing OVD is not determinedby the anterior but posterior teeth. This is clearlyillustrated with bulimic erosion of anterior teeth.In this scenario, the anterior teeth lose incisalheight, but due to over-eruption, anterior centriccontact is re-established. However, the posteriorteeth are intact without showing signs of wear.In these circumstances, the anterior teeth requireeither orthodontic intrusion or surgical crownlengthening. Carrying out extensive restorationson the posterior teeth for increasing OVD isunjustified.

Facial dimensions are another spuriousmethod for OVD determination.30 For idealfacial dimensions, the middle-face (from eye-brows to base of the nose) should equal thelower-face (base of nose to tip of chin). The latteris genetically determined, and if a patient has ashort chin, should the OVD be increased to com-pensate for this anatomical anomaly? Cephalo-metric analysis is invaluable for orthodontictooth movement, when both soft tissues and thealveolus are altered for restorative dentistry;when only the teeth are affected, however, its useis limited. Finally, lengths of the masseter andmedial pterygoid muscles are yet another sug-gested method. The latter is simply calculated by geometric analysis of the condylar positionrelative to the muscles and anterior teeth. For every 3mm anterior opening, the masseterlength increases by 1mm, but due to the 1 mmposterior seating of the condyles, the apparentincrease in muscle length is nullified. Therefore,altering the OVD anteriorly by up to 3mm has no effect on muscle length; muscle length is therefore not an accurate determinant of OVD.

Having outlined methods for OVD determi-nation, the next step is altering the OVD. This isprimarily carried out for improving anterior aes-thetics, gaining space for dental prostheses oraltering the occlusion. The first myth to dispelabout altering OVD is that there is no such thingas an ideal vertical dimension. Consequently,performing extensive dentistry for attaining thiserroneous goal is not only futile, but also grosslyunethical.

As a general guideline, an anterior opening of3mm produces posterior space of 1mm. Asstated previously, with this amount of increase inOVD the masseter is lengthened by 1mm, butbecause the condyles seat 1mm posteriorly theincreased muscle length is negated (Figs. 2.35 & 2.36). Put another way, an anterior increaseof 3mm is tolerable without any muscular adap-tation or pain.31 However, if the increase isgreater than 3mm, certain concerns need to beaddressed:

� Pain associated with an increase in OVD isephemeral, usually subsiding within 2 weeks

Figure 2.34 Disparity of gingival zeniths of the maxillarycentrals.


� In certain patients there is a degree of relapsewhen the OVD is increased, by remodellingof the alveolar bone and muscular adapta-tion, stabilising in 6 months. Therefore, ifthe precise increase in OVD is crucial, it iswise to place temporaries and wait 6 monthsbefore progressing to the definitive restorations

� Increased bite forces could potentially bedetrimental to new prostheses. Initially thereis an increase in bite force, which normaliseswithin 3 months, and is of no clinical significance

� Violation of the freeway space may causeconcern. When fabricating dentures for anedentulous patient, the freeway space of 2–4mm is essential for preventing the upperand lower dentures clicking during speech ormastication.32 However, in the dentatepatient, the proprioceptive response of theperiodontal ligament ensures that if thefreeway space is encroached, neuromuscularadaptation recreates the freeway spacewithin 2–4 weeks

Phonetics

The second part of function is unimpeded pho-netics, verified by speaking certain words orletters such as the ‘M’, ‘S’, ‘F’ or ‘V’. The ‘M’sound, erroneously referred to as the rest posi-tion, is when the teeth are separated with afreeway space (Fig. 2.37). In fact, this position is

not one of rest, but a habitual muscular positionof the mandible.33 A true rest position is observedwhen the elevator muscles are completelyrelaxed, such as during sleep. This ‘M’ positionassesses the amount of maxillary incisal displayand confirms that the freeway space has‘returned’, following an increase in the OVD.The ‘F’ sound determines the sagittal inclinationof the maxillary incisors. If correct, the buccalaspects of incisal third of the maxillary incisorsshould contact the mucosal, not the cutaneous,part of the lower lip (Fig. 2.38). If contact isabsent, the incisors may be either too short orprotruded.34

Figure 2.35 Proposed increase in OVD to enhance functionand aesthetics (laboratory work by Gerald Ubassy, France).

Figure 2.36 Proposed increase in OVD to enhance functionand aesthetics (laboratory work by Gerald Ubassy, France).

Figure 2.37 Phonetics: the ‘M’ sound. Habitual muscularposition for determining amount of maxillary incisor display.


Finally, the ‘S’ sound assesses the verticaldimension of speech (Fig. 2.39). In order to avoidlisping, a 1mm separation between the maxillaryand mandibular incisors is necessary. Two sce-narios are evident:

� The patient postures the mandibular incisorsforward to make the ‘S’ sound, i.e. the pos-tural position of the mandible is NOT coin-cident with CO. In this situation, adjustingthe incisors (usually shortening the mandibu-lar incisors) re-creates the requisite 1mmseparation. However, when the patient nowoccludes in CO, there is lack of contactbetween the anterior teeth. The latter iseasily corrected by addition of the relevant

restorative material(s) to the palatal aspectof the maxillary incisors

� The mandible coincides with CO during the‘S’ sound, evident in some Class II and IIIocclusions. Adjusting the incisors to obtain1mm separation to prevent lisping will obvi-ously create an unwanted anterior space. Inthese cases, the only option is to close theOVD posteriorly to obtain centric contactbetween maxillary and mandibular incisors

Aesthetics

Dental aesthetics is a vast topic, encompassingmany scientific and artistic principles. Thesection below on aesthetics is not exhaustive, butfurnishes the reader with basic outlines and prac-tical guidelines for providing aesthetic restora-tions. For a detailed analysis, further reading isessential to grasp the theoretical concepts per-taining to dental aesthetics.35

Aesthetics is an art, not a science.36 But like so many works of art, scientific principles areused for creating aesthetics. The morphology of animals and plants is based on fundamental geometric principles, with modifications, tocreate beings that are unique (Figs. 2.40 & 2.41).Dental aesthetics are also governed by mathe-matical concepts to create unique artificial pros-

Figure 2.38 Phonetics: the ‘F’ and ‘V’ sounds. Maxillaryincisors touching mucosal part of mandibular lip.

Figure 2.39 Phonetics: the ‘S’ sound. Vertical dimension ofspeech.

Figure 2.40 Innate beauty of plants can be related to math-ematical concepts of beauty.


theses. Nature, however, goes one step further byusing its ‘imagination’, and avoids generatingclones of a particular species. Geometric laws arenot ‘carved in stone’, but are invaluable as astarting point for inspiration as opposed to emulation. The ensuing discussion outlines basicgeometric rules for the anterior maxillary sixteeth, which the clinician can readily incorporateinto daily practice for an aesthetic prescription.

The starting point of an aesthetic appraisal islistening to the desires and wishes of the patient.Patients have an image of themselves, which theyproject and preserve. This image is constantlyfluctuating by the id, peer and media pressure.Whilst these opinions are highly subjective, theonly objective method of aesthetic analysis ismathematical. Indeed, mathematical languagehas been considered the only reference by whichnature can be comprehended.37 The clinicianshould therefore be familiar with geometric con-cepts governing anterior dental aesthetics. Forelucidation, dental aesthetics can be arbitrarilydivided into four compositions; facial, dentofa-cial, dental and gingival (Figs. 2.42–2.45).

Facial composition

The facial composition is the one most importantto the patient. This composition influences mostpatients’ preconceived ideas of a ‘perfect smile’.

Figure 2.41 Innate beauty of plants can be related to math-ematical concepts of beauty.

Figure 2.42 Facial composition.

Figure 2.43 Dentofacial composition.

Figure 2.44 Dental composition.


The reason for this is that most media images ofbeauty are concentrated around the face. Thepublic is rarely accustomed to viewing a smile ata close distance that is routine in dentistry. At thefacial distance of focus, the teeth appear whiteand straight. At a closer field of view, forexample the dentofacial composition, the teethrarely exhibit exact regularity, but have distinctproportions and embrasures. It is important toconvey this to the layman, so that he or sheappreciates that the media image is only oneaspect of a smile.

Two aspects are significant when analysing theface: the frontal and sagittal. From the frontalaspect, numerous landmarks are used as guidesfor aesthetic appraisal. Horizontally, severalimaginary reference lines are discernible, com-mencing from the upper to lower part of the faceincluding the hair, ophriac, interpupillary, inter-alar and commissural lines. These parallel linescreate horizontal symmetry, acting as cohesiveforces to unify the facial composition. The facialmidline is perpendicular to the horizontal linesand opposes their cohesiveness. These are termedsegregative forces and are essential in a compo-sition to add interest and harmony (Fig. 2.46).The cohesive forces are paramount for achievingpleasing aesthetics; the deviation of the facialmidline is secondary, varying in many individu-als without a deleterious effect. It is the generalparallelism of the horizontal lines which isimportant, rather than orientation of a specificline.38

The interpupillary line is used as a referencefor the occlusal and incisal plane orientations.The other horizontal lines can be eschewed andtherefore do not act as definite references; butthey are useful accessory makers (Fig. 2.47). Theincisal edges of the anterior teeth should be par-allel to the interpupillary line and perpendicularto the midline (Fig. 2.48). Canting of the incisalplane is attributed to either dental or skeletalfactors. The dental factors include wear (attri-tion, erosion, abrasion), altered patterns of erup-tion or periodontal disease. If the dental factorsare eliminated, the tilting could be due to aslanted maxilla. It is crucial to ascertain causes

Figure 2.45 Gingival composition. Figure 2.46 Parallelism of facial lines results in horizontalsymmetry.

Figure 2.47 Frequently, the secondary facial lines areeschewed, and absolute parallelism is not a prerequisite foraesthetic appraisal.


of misalignment of the incisal plane, since these impact on the proposed treatment plan(Fig. 2.49).

From the sagittal aspect, the horizontal linesalso reinforce the cohesiveness of the profile (Fig.2.50). In this aspect two additional referencelines require consideration: the nasolabial angle(Fig. 2.51) and the Rickett’s E-plane (Fig. 2.52).39

The nasolabial angle is formed by the intersec-tion of two lines using the nose and lips as ref-erence points. For males this angle ranges from90–95° and for females from 100–105°. TheRickett’s E-plane is a line drawn from the tip ofthe nose to the chin prominence. Accepted normsfor the distance from the upper lip to this imag-inary line is 4mm, while that for lower lip is

Figure 2.48 Coincidence of the interpupillary and incisalplane lines is used as a guide for dental aesthetics.

Figure 2.49 Uneven attrition and wear resulting in tilting ofthe incisal plane.

Figure 2.50 Sagittal view showing parallelism of the faciallines.

Figure 2.51 Nasolabial angle (golden highlight).

Figure 2.52 Rickett’s E-plane.


2mm. Using the nasolabial angle and Rickett’s E-plane, the protrusion or retrusion of the maxillacan be assessed. Assuming 90° as the normal, ifthe nasolabial angle is <90°, and the distance ofthe upper lip to the E-plane is greater than 4mm,the maxilla is prominent and the facial profile isconvex. In these cases, less dominant maxillaryanterior restorations should be considered. If the reverse, a concave profile is evident, i.e.nasolabial angle is >90°, and the distance of theupper lip to the E-plane is <4mm, a prominentmaxillary anterior dental sextant is desirable.Spear40 has termed this concept of facial profileto determine the position and degree of domi-nance of the maxillary anterior teeth as ‘faciallygenerated treatment planning’.

Dentofacial composition

The second constituent of anterior dental aes-thetics is the orofacial view known as the dentofacial composition, consisting of the teethsurrounded by the highly vascularised lips. Thered colour of the lips and the lighter teeth createa colour contrast, adding interest to this compo-sition. The aesthetic appraisal of this view isdetermined by two muscular positions, the staticand dynamic.

Static

In the static position, the lips are slightly parted,the teeth out of occlusion. This is a habitual mus-cular position, often incorrectly referred to as the‘rest position’. In this position four features influ-ence tooth exposure: lip length, age, race andsex, known as the LARS factor (Figs. 2.53–2.56).41 Table 2.2 displays the amount of maxil-lary and mandibular central incisor teeth visiblein relation to the length of the maxillary lip. Thelength of the upper lip varies from 10–36mm,and individuals with a long maxillary lip showmore mandibular than maxillary incisors.

Age is the second part of the LARS factorwhich, in a similar manner to lip length, influ-ences the amount of tooth visibility. The amountof maxillary incisor tooth display is inverselyproportional to increasing age, while degree of

Figure 2.53 Maxillary lip length determines the degree ofmaxillary incisor display.

Figure 2.54 Elderly males have long maxillary lips, withreduced maxillary incisor display.

Figure 2.55 Black individuals have longer maxillary lips,with reduced maxillary incisor display.


mandibular incisor display is directly propor-tional to increasing age.

People age at different rates, because ageing isa multifactorial phenomenon described by thethree Ps:

� Programmed ageing� Pathological ageing� Psychological ageing

In youth, the process of destruction and for-mation of cells is in a state of equilibrium. Withadvancing years the balance shifts in favour ofincreased destruction and reduced replacement.This change is triggered by an internal ‘biologi-cal clock’, the reason for which is unknown.Pathological ageing is due to diseases of the oralcavity and surrounding structures leading to anaccelerated degradation of tissues. For example,

if anterior teeth are lost due to refractory peri-odontitis, there is premature development ofnasolabial grooves (Fig. 2.57). Psychologicalageing is the result of psychosomatic changes dueto emotional and personal traumas. Irrespectiveof cause, the three Ps of ageing cause reducedtonicity of the orofacial muscles and laxness oftegumental relief in the lower third of the face.This leads to formation of the labial, nasolabialand mental grooves and ridges. The loss of elas-ticity and tooth support (gingival two-thirds ofupper incisor) of the upper lip accounts for lessmaxillary and more mandibular incisors displayat rest. Attrition is another factor in the aged,contributing to further reduced amount of toothdisplay.

The last two determinants of the LARS factorare race and sex. A decreasing amount of max-

Figure 2.56 Females have short maxillary lips, withincreased maxillary incisor display.

Table 2.2 Maxillary lip length in relation to anterior tooth exposure.

Maxillary lip Maxillary lip Exposure of maxillary Exposure of mandibular length (mm) central incisors (mm) central incisors (mm)

Short 10–15 3.92 0.64Medium 16–20 3.44 0.77Medium 21–25 2.18 0.98Long 26–30 0.93 1.95Long 31–36 0.25 2.25

Figure 2.57 Early tooth loss due to periodontitis results inaccelerated formation of nasolabial grooves.


illary and increasing amount of mandibulartooth visibility is evident from Caucasians,Asians to Blacks. Finally, gender considerationsreveal that females display nearly twice theamount of tooth as compared to men, 3.40mmand 1.91mm, respectively.

In conclusion, each patient should be assessedaccording to the LARS factor before finalisingthe final amount of tooth exposure in the staticposition, e.g. an increased maxillary toothdisplay is indicated for young females, while theopposite is true for elderly men.

Dynamic

The dynamic position of the dentofacial compo-sition is characterised by a smile. The extent oftooth exposure during a smile varies, dependingon the degree of contraction of the facialmuscles, the shape and thickness of the lips, theskeletal make-up, and the shape and size of thedental elements. Whereas in the facial composi-tion horizontal symmetry was the most impor-tant factor, in the dentofacial view it is radiatingsymmetry that takes precedence. Radiating sym-metry is the central point of an object fromwhich the right and left sides are mirror images.42

In the dental context, the maxillary dentalmidline is the fulcrum or central point, and theright and left upper anterior teeth are balancedmirror images. This is relatively uncommon dueto erratic patterns of wear and attrition of theincisal and canine edges. Lack of radiating sym-metry is not crucial, so long as there is balanceon the right and left sides of the anterior dentalsextant (Fig. 2.58). The incisal plane and com-missural lines should coincide to act as cohesiveforces, and the dental midline as the segregativeforce, adding interest to the composition (Fig.2.59).

Placement of the dental midline has evokedconsiderable controversy in the dental literature.One school of thought states that the maxillarydental midline should coincide exactly with thelabial frenum and the facial midline43 as it doesin 70% of the population. The opposing viewstates that placing the midline exactly in thecentre contributes to a sense of artificiality.44

Where to place this midline should be deter-

mined after an aesthetic appraisal. If a dominantcentral point of focus exists, e.g. a maxillarymedian diastema, then the midline should beplaced with this focal point as the fulcrum.Another reason for placing a vertically alignedmidline precisely in the centre is to detract atten-tion from asymmetries and disharmonies of theface. The concept of guiding the eye to a partic-ular point of focus on the face is extensively usedby opticians and the cosmetic industry with greateffect. On the other hand, a slightly off-centreplacement of the dental midline, in relation to thefacial midline, is not detrimental to aestheticapproval (Figs. 2.60 & 2.61). The mandibular

Figure 2.58 Balance: perfect alignment of the anterior max-illary sextant is less important than balance on contralateralsides.

Figure 2.59 Ideally, the commissural plane (blue) shouldcoincide with the incisal plane (lime green) and be perpen-dicular to the dental midline (yellow).


midline should not be used as a reference point,because in 75% of cases this does not coincidewith the maxillary midline.45

The smile line is an imaginary line of the tipsof the maxillary teeth, parallel to the curvatureof the mandibular lip (Fig. 2.62). The coinci-dence between the incisal table and the lower lipis often lost because of wear, and, if possible,should be restored by restorative procedures.The anterior and lateral negative spaces act as aborder to the dental elements, similar to theborder around a painting, while the lips repre-sent a frame. Anterior negative space is evidentduring speech and laughter (Fig. 2.63), while thebilateral negative spaces are seen during a smile(Fig. 2.64). These negative spaces provide cohe-

Figure 2.60 For a pleasing appearance, coincidence of thefacial and dental midlines is not mandatory.

Figure 2.61 For a pleasing appearance, coincidence of thefacial and dental midlines is not mandatory.

Figure 2.62 Parallelism of the incisal plane with the curva-ture of the mandibular lip.

Figure 2.63 Anterior negative space during laughter.

Figure 2.64 Bilateral negative space.


siveness and a frame to the dentofacial composi-tion.46 Some authorities advocate elimination of bilateral negative spaces, during a so-called‘complete aesthetics makeover’. This results inexcessive tooth display during a smile conveyingartificiality, and is unwarranted because of irre-versible destructive prosthetic procedures.

To summarise, the perfect smile is when theupper anterior teeth are in line with the curva-ture of the lower lip, the corners of the lips areelevated to the same height on both sides (smilesymmetry), with bilateral negative space sepa-rating the teeth from the corners of the lips (Fig.2.65).

Dental composition

The dental composition consists of the teeth (sizeand shape), and their intra- and inter-arch rela-tionships. Tooth size is determined by measuringthe inciso-gingival length and dividing by themesio-distal width to obtain the width/lengthratio:

Clinicians and authors have subjective opin-ions, as no definitive value exists for the w/l ratio.The mesio-distal width is more important thanthe inciso-gingival length47, and it is the formermeasurement that has attracted much debate.

width length w l ratio of a tooth( ) = widthlength

Research has focused on measurements ofextracted orthodontic teeth, racial and genderdifferences, and facial landmarks such as thebizygomatic width. The latter was described byHouse and Loop48 who stated that the mesio-distal measurement of the central incisor was1/16 of the bizygomatic width. Other studieshave assigned geometric values to the mesio-distal width of the centrals to the size of the face,while Rufenacht49 has proposed morphopsycho-logical determination of the ideal proportion andsuggested that the width of the central incisorshould be considered constant throughout life.Which theory a clinician chooses is open to dis-cussion as none of the research is conclusive.Nevertheless, general guidelines are necessary tocreate pleasing dimensions:

� The w/l ratio of the central incisor shouldrange from 0.75–0.8, less than this valuecreates a long narrow tooth, while a largerw/l ratio results in a short wide tooth (Fig.2.66)

� The central incisor is dominant in the ante-rior dental composition (Fig. 2.67)

� The vertical overbite in relation to speechrequires attention (discussed above).

Besides these fundamental principles, subtlevariations can be introduced, accounting for sex,race, morphopsychological and facial factors.

Figure 2.65 The ‘perfect’ smile. Figure 2.66 Width/length ratio. Blue tooth – wide (0.8); redtooth – ‘ideal’ (0.75); green tooth – narrow (0.6).


The shape of the upper anterior teeth is alsowidely debated. The two prominent studies are by Williams50 and Frush and Fisher.51,52,53

Williams established a relationship between theshape of the central incisor and the face, whileFrush and Fisher related sex, age and personal-ity (SAP) to the contour of the anterior dentalsegment. The Williams theory was invalidated by subsequent studies. The Frush and Fisherconcept is concerned with the dominance of thecentral incisor and its wear in advancing years.Other theories have proposed a correlation oftooth shape to skeletal and soft tissue landmarks,but have proved inconclusive. The shape of teethis inherited, and if possible, the prosthodontistshould obtain pictures of patients’ relativesbefore determining the final shape of anteriorteeth. If this is not possible, the items to considerare age, sex, race and personality. For example,youthful teeth have sharp, unworn incisal edges;the centrals dominate the composition, and arein harmony with the laterals and canines.

The next factor to consider is tooth-to-toothprogression. Ancient Greeks endeavoured to formulate beauty as an exact mathematical principle. They believed that beauty could bequantified and represented in a mathematicalformula. This lead Pythagoras to conceive theGolden proportion (1/1.618 = 0.618), and Platothe Beautiful proportion (1/1.733 = 0.577). Bothideas stipulate that an object with specific pro-portions is perceived as having innate beauty.

The most widely used concept in dentistry is theGolden proportion, whose formula is as follows:

where S is the smaller and L the larger part. Theuniqueness of this ratio is that when applied bythree different methods of calculations, linear,geometric and arithmetic, the proportional pro-gression from the smaller to the larger to thewhole part always produces the same results.This concept has been described by Lombardi54

and Levin55 (Fig. 2.68). However, researchershave indicated that a Golden proportion is notalways evident, and variations are often appar-ent in the natural dentition.56 It is imperative tomention that many healthy dentitions do notconform to this ‘ideal’ ratio, but are still per-ceived as aesthetically pleasing (Fig. 2.69). Tocreate an aesthetically pleasing result, the mostimportant aspect is repeating proportions, ratherthan a specific ratio. Therefore, providing ‘cos-metic dentistry’ for healthy teeth not in the idealratio 0.618 is grossly unnecessary and highlyunethical.

The axial inclination of the maxillary anteriorteeth is ideally aligned so that the incisal edgesconverge mesially (Fig. 2.70). The contact pointsare also coincident with the incisal edges and thecurvature of the lower lip, enhancing the cohe-siveness of the dentofacial composition.

Incisal embrasures have a distinct appearancedepending on age and sex. For virgin teeth, anincrease of the embrasure angle from the maxil-lary central incisor to the canine is apparent (Fig.2.71). Pronounced embrasures are a feature ofyouth or femininity, while shortened, worn edgesconvey advancing age or masculinity (Fig. 2.72).Discussion with the patient is essential to incor-porate their wishes and desires, before decidingon the angle of the incisal embrasures.

The buccolingual thickness of teeth varies, e.g.the upper central incisor has a range between 2.5and 3.3mm.57 This is measured with a widthgauge at the junction of the middle third andincisal third of the tooth (Fig. 2.73). If the buc-colingual thickness of a prosthesis is more than3.5mm, over-contouring should be suspected.

SL

LS L

=+

=+

=21 5

0 618.

Figure 2.67 The dominance of the maxillary central isessential for a pleasing smile.


Figure 2.68 The Golden proportion.

Figure 2.69 Although not in the Golden proportion, thisnatural dentition is nevertheless aesthetically pleasing.

Figure 2.70 Mesial axial inclination of maxillary anteriorteeth.


This is usually caused by insufficient tooth preparation, leaving inadequate space for therestorative materials, resulting in a bulbousrestoration (Fig. 2.74). If the buccolingual thick-ness is less than 2.5mm, elective endodontictherapy may be necessary to achieve the desiredaesthetic result.

Gingival composition

The gingival apparatus is the last constitutent ofaesthetic appraisal. Gingival contour mimics theunderlying bone architecture. The gingival zenithis the most apical part of the FGM and is locateddistally for the maxillary central and canine, andin line for the lateral, to the long axis of thetooth. This zenith disappears due to poor den-tistry, but can be regained by replacing defectiverestorations (Figs. 2.75 & 2.76).

Extension of the FGM apically from thecontact point to the attached gingiva forms theinterdental papilla. Following recession, peri-odontal or iatrogenic insult, the gingival embra-sures become visible and form so-called ‘blacktriangles’ (Fig. 2.77). Numerous techniques forpreserving58 and restoring59 the interdentalpapilla have been described, and the prostho-dontist should strive to fill these open gingivalembrasures for optimal aesthetics.

During a relaxed ‘ideal smile’, the upper lipexposes the cervical aspects of the upper anterior

Figure 2.71 Pristine virgin teeth with pronounced incisalembrasures.

Figure 2.72 Worn aged teeth with flat incisal embrasures.

Figure 2.73 Bucco-lingual thickness.

Figure 2.74 Over-contoured, bulbous crown.


teeth. The gingival margins of the maxillarycentral should be at the same height, and sym-metrical. Up to 3mm exposure above the cervical margins of the teeth is aestheticallyacceptable (Fig. 2.78).60 More than 3mm expo-sure leads to a ‘gummy’ smile, requiring correc-tion in order to avoid visual tension (Fig. 2.79).Treatment modalities depend on the type ofpathosis, e.g. hyperplastic gingivae require gin-givectomy or crown lengthening; recession canbe corrected by cosmetic periodontal plasticsurgery using tissue grafts or guided tissue regen-erative membranes; over-eruption by orthodon-tic intrusion; deficient pontic sites by ridge

Figure 2.75 Amorphous free gingival margin associatedwith defective crown on maxillary right central incisor.

Figure 2.76 Replacement crown for patient in Figure 2.75,and following gingival health the gingival zenith peaks distalto long axis of tooth.

Figure 2.77 Gingival embrasures causing ‘black triangles’between defective metal–ceramic crowns.

Figure 2.78 Up to 3mm of gingival exposure during arelaxed smile is acceptable for a pleasing smile.

Figure 2.79 Greater than 3mm of gingival exposure is aes-thetically unacceptable.


augmentation procedures; and skeletal abnor-malities by orthognathic surgery.

One of the most significant features of gingival aesthetics is its contour progressionfrom the incisors to canine. The gingival aes-thetic line (GAL) can be defined as a line joiningthe tangents of the zeniths of the gingivalmargins of the central incisor and canine. TheGAL angle (GA) is the intersection of the GAL line with the maxillary dental midline (Fig.2.80). Assuming a normal w/l ratio, anatomy,position and alignment of the anterior dentalsegment, four classes of GAL are described, asfollows:

� Class I – the GAL angle is between 45° and90° and the lateral incisor is touching orbelow (1–2mm) the GAL (Fig. 2.81)

� Class II – the GAL angle is between 45° and90° but the lateral incisor is above (1–2mm)the GAL and its mesial part overlaps thedistal aspect of the central incisor. This situ-ation often occurs in Angle’s class II orpseudo-class II conditions, adding variety tothe dental composition (Fig. 2.82)

� Class III – the GAL angle is 90°, and thecanine, lateral and central all lie below theGAL (Fig. 2.83)

� Class IV – the gingival contour can not beassigned to any of the above three classes.The GAL angle can be acute or obtuse. Amyriad of gingival conditions present as gingival asymmetries, including recession,altered patterns of eruption, loss of inter-dental papillae, clefts and high frenal inser-tions (Fig. 2.84)

Figure 2.80 The GAL classification for gingival contour progression.


In a single mouth, the right and left sides candisplay different GAL classes (Fig. 2.85). Theaim is to restore the gingival contour to a GALclass I, II or III in order to achieve aestheticapproval and favourable ‘pink aesthetics’.

Table 2.3 summarises the salient items to con-sider during an aesthetic appraisal.

Figure 2.81 GAL class I.

Figure 2.82 GAL class II.

Figure 2.83 GAL class III.

Figure 2.84 GAL class IV.

Figure 2.85 GAL class I on right maxillary sextant and GALclass III on left maxillary sextant.


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Table 2.3 Aesthetic appraisal.

Composition Evaluate Determine by . . .

Facial Cohesive forces (horizontal symmetry) Horizontal facial linesSegregative forces Facial midlineIncisal plane Relation to interpupillary lineProtrusion/retrusion of maxilla Rickett’s E-plane and nasolabial angle

Dentofacial Tooth exposure in static position LARS factorTooth exposure during a smile Radiating symmetryFulcrum of smile Dental midlineSmile line Relation of maxillary teeth to lower lip during a smile

Dental Tooth dimensions Width/length ratioTooth morphology Genetics (hereditary)Tooth-to-tooth relationship Modified Golden proportion, repeated proportion more

significant than a specific ratioAxial inclination Mesially inclined maxillary anterior dental segmentIncisal embrasures Age, sex and personalityBuccolingual thickness Normal range = 2.5–3.3mmPhonetics M, F, V and S sounds

Gingival Contour around individual tooth Underlying bone architecture and tooth morphologyExposure during smile Acceptable range is less than or equal to 3mmContour progression from central GAL and GA

incisor to canine


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Having established an ideal treatment modalityusing APT and the HFA triad in the previous twochapters, the clinician, ceramist and patient are now confronted with choosing the type ofrestoration which will achieve these objectives.The dental market is awash with crown systems,with wide-ranging claims. However, it should be emphasised that no system offers everything,and, very often, a compromise is inevitable. Thediscussion below concentrates on all-ceramicsystems, allowing the operator to select the mostappropriate material for a given clinical situa-tion. The clinical performance of all-ceramicrestorations is influenced by many factors, whichare discussed in other chapters of this book,including material properties, tooth preparationdesign, fabrication, luting, occlusion and fatigue.This chapter is limited to material properties ofvarious ceramics.

SCIENTIFIC RATIONALE

Rationale for all-ceramic restorations

The first question to ask is ‘Why?’ Why choosean all-ceramic, rather than a metal–ceramic

restoration? It is a fait accompli that metal–ceramic restorations have exhibited remarkabledurability since their introduction over fourdecades ago. The major reason for this success is attributed to the relatively forgiving and established clinical and laboratory techniques.While mechanical endurance of metal–ceramicrestorations is undisputed, their major dis-advantage is poor appearance in aestheticallychallenging areas of the mouth. In these cir-cumstances, the familiar shadowing or metalshine-through at the cervical margins severelycompromises aesthetics. Additionally, corrosionby-products and allergic responses to castingalloy constituents are also a concern. These dis-advantages have fuelled the introduction of all-ceramic systems, with superior aesthetics andbiocompatibility, and elimination of unwantedcorrosion or allergic responses. The rationale forimproved aesthetics with ceramic prostheses is asfollows.

A tooth appears ‘natural’ due to the inter-action of light with dental tissues. The processby which light interacts with dentine and enamelis complex, consisting of reflection, transmission,diffusion, fluorescence, opalescence and iride-scence, which are elaborated further in Chapter4 (Colour and Shade Analysis). Nevertheless, forthe present discussion, the following simplified

3Choice of all-ceramic systems


explanation is sufficient. Light enters a tooth bytwo pathways, via the root through the peri-odontium, and the crown, the part that is visiblein the oral cavity (Figs. 3.1 & 3.2). The vitalityand authenticity of natural dentition is due to the unimpeded mingling of light rays throughthese two routes. Ideally, an artificial restorationshould endeavour to emulate this free flow oflight within the entire tooth structure (Fig. 3.3).

This phenomenon is illustrated by models of anatural tooth, a metal–ceramic crown and an all-ceramic crown (Figs. 3.4–3.6). In a natural tooth,blue light (representing light entering the root)and red light (representing light entering fromthe crown) is free to mingle, and utilise 100% ofthe optical capacity of enamel and dentine (Fig.3.7). When a metal–ceramic crown is placed on

Figure 3.1 Light entering a tooth by the root via the periodontium.

Figure 3.2 Light entering a tooth by the crown.

Figure 3.3 The vitality of natural dentition is attributed tounimpeded light flow through the root and crown of a tooth.

Figure 3.4 Sectioned natural tooth.

Figure 3.5 Section tooth with metal–ceramic crown.

Choice of all-ceramic systems 57

to a tooth, the metal substructure blocks 90%(by surface area) of the optical capacity of atooth. In effect, aesthetics, or appearance, of themetal–ceramic crown is limited to the veneeringporcelain, less than 10% of the surface area (Fig.3.8). Although not impossible, it is extremely difficult to simulate the entire optics of a toothwithin only 10% of its surface area. The ceramistis faced with mimicking light flow of the entiretooth in the veneering porcelain, which requiresskill and a high degree of aptitude. If notachieved, the resultant metal–ceramic crownappears artificial and dull, often with greying orshadowing at the cervical margin.

With an all-ceramic crown, similar to a naturaltooth, light is able to flow freely, utilising 100%

of the optical capacity of enamel and dentine(Fig. 3.9). Hence, all-ceramic restorations displayvitality, vibrancy, and are often indistinguishablefrom the surrounding natural dentition. Theoptical advantage of all-ceramic units helps theceramist to create life-like restorations, withoutthe constraints of working within the limitedsurface area of the veneering porcelain. This isalso relevant when using posts for non-vital teeth that require intra-radicular support, sincemetallic posts hinder light transmission into theroot.

Figure 3.6 Sectioned tooth with all-ceramic crown.

Figure 3.7 Natural tooth: light entering through the root(blue) is free to mingle with light entering from the crown(red).

Figure 3.8 Metal–ceramic crown: the metal substructureblocks all light via the root (blue), and aesthetics or appear-ance of the crown is limited to the veneering porcelain (red).

Figure 3.9 All-ceramic crown: light via the root (blue) andcrown (red) is free to mingle (red), similar to in a natural tooth,especially at the crucial cervical area.


Physical and mechanical properties of ceramic

Generally, a high-glass content yields superioroptical properties, but inferior mechanicalstrength (e.g. feldspathic and leucite-reinforcedglass ceramics). The opposite is true for low-glasscontent, which has better mechanical strengthbut reduced translucency (e.g. pure densely sin-tered alumina and zirconia). Of course, opticalproperties alone are insufficient for a ceramic toperform adequately in the oral cavity. Addition-ally, a ceramic should possess sufficient strength(flexural strength, fracture toughness), longevity(resistance to fracture), reduced wear of oppos-ing teeth and biocompatibility. Finally, simple,expedient and precise laboratory protocols aredesirable for ease of manipulation for facilitatingfabrication of the restoration, e.g. possessing alinear coefficient of thermal expansion.

The following properties are applicable formost ceramics, while specific differences of agiven class of ceramic are discussed later. Ceram-ics are highly biocompatible with dental tissues,producing few allergic reactions or corrosion by-products that plague certain dental restorations.1

They are also chromatically stable and plaquerepellent, with insignificant colour change overtime, and diminished staining, respectively.2

Another concern with older feldspathic por-celains is pronounced hardness, leading tounwanted opposing tooth wear; this can be asmuch as 230µm per annum,3 in comparison tonatural enamel-to-enamel wear of only 60µmper annum. The smallest amount of wear is withgold restoration (9µm per annum). However,newer low-fusing porcelains have an annualwear comparable to natural teeth at approxi-mately 60µm per annum.

Uni-layer and bi-layer all-ceramic systems

All porcelains, from the early feldspathic to thelatest zirconia ceramics, are beleaguered withinherent brittleness and low fracture toughness;these compromise mechanical resilience and,

ultimately, longevity. In order for a ceramic to endure the oral environment, it must be adequately supported. Unsupported porcelain,because of its inherent high modulus of elastic-ity (MOE) (brittleness), is prone to fractureunder masticatory loads. There are two solutionsto this predicament. The first is to gain supportfrom the underlying tooth to dissipate occlusalforces. The second is to support the weakerveneering porcelain by a stronger substructure.Both methods are used for different all-ceramicsystems.

To gain support from natural tooth involvesadhesive bonding to form a unified structure. Toachieve this, the ceramic must be amenable toetching with hydrofluoric acid. This is followedby silane application of the intaglio surface and bonding the restoration to dentine usingdentine bonding agents (DBAs) and appropriateresin luting cements. The ceramics conducive to etching with hydrofluoric acid are the silica-based varieties, e.g. feldspathic, or pressedceramics. Before the advent of silane couplingagents, most porcelain laminate veneer (PLV)failures were attributed to lack of adhesion to the underlying tooth. Silane resolved this issue by forming a chemical link between etched feldspathic porcelain and the underlying tooth, creating a hermetic seal between two disparate materials, with the natural tooth actingas the support for the brittle porcelain. This type of all-ceramic system, in which the supportof the porcelain is gained from the natural tooth, is termed a uni-layer all-ceramic system(Fig. 3.10).

Instead of using the natural tooth for asupport, the alternative is a resilient infrastruc-ture to support the fragile veneering porcelain.The initial substructures were casting alloys formetal–ceramic restorations. To circumvent pooraesthetics of the latter, high-strength ceramics,such as alumina or zirconia, can be a substitutefor the metallic substructure, which also obviatesthe necessity to gain support from the underly-ing tooth. This is termed a bi-layer all-ceramicsystem, and is employed by most of the currentlyavailable ceramic systems (Fig. 3.11). Further-more, the intaglio surfaces of restorations fabri-cated from alumina and zirconia are not etchable


with hydrofluoric acid, and adhesive cementa-tion no longer a pre-requisite. However, bondingceramics to tooth is still desirable, and therecently introduced adhesive resin cements arepromising for achieving a chemical bond, similarto that with silane coupling agents to silica-basedceramics (see Chapter 10).

Aetiology of fractures

The major cause of failure of all-ceramic units isfracturing. Preventing fractures is not limited to

material properties, but heavily reliant on correctclinical and laboratory protocols. These factorsare often ignored, and fractures are blamed on the ceramic material. The reason for this istwofold:

� Clinical and laboratory techniques formetal–ceramics are relatively forgiving,allowing a degree of latitude

� There is always inertia to change from established materials and protocols such as metal–ceramic prostheses, which havebecome routine in the last four decades

When considering all-ceramic units, a para-digm shift regarding techniques is essential.Ceramic systems are unforgiving, demanding adifferent, more stringent protocol for long-termsuccess. If this aspect is ignored, failure isinevitable. Furthermore, a balance is necessary:all-ceramic restorations are not indicated forevery clinical situation, and for certain scenarios,metal–ceramics are more predictable. However,if judicially chosen and skilfully executed, all-ceramic restorations provide years of reliableservice for aesthetically sensitive regions of themouth.

Since fracture is the most prevalent cause offailure of all-ceramic units, a clear understand-ing of crack formation and propagation ismandatory. An inherently brittle substance, such as a ceramic, has innate microscopic flaws(cracks and pores) statistically distributed withinthe material. These are termed Griffith’s flaws,4

formed during fabrication and adjustments, andtheir propagation reduces fracture toughness ofthe material. Additionally, fracture toughness is time-dependent, reducing the strength of the ceramic over time.5 If a ceramic is left undis-turbed in an inert environment, the flaws areinconsequential. However, when exposed to adynamic environment, for example the oralcavity, these flaws undergo so-called subcriticalcrack growth, eventually resulting in fractures.The humid environment, with or without normalfunctional and dysfunctional occlusal stresses,causes static fatigue and stress-corrosion, result-ing in crack growth and eventual catastrophicfractures (Figs. 3.12 & 3.13).

Figure 3.10 Uni-layer ceramic restorations: silhouette ofcross-sections of porcelain laminate veneers.

Figure 3.11 Bi-layer ceramic restorations: a dense ceramiccore (blue) is veneered with an overlying porcelain (red).


The average bite force is greatest in the firstmolar region and least in the incisor region. Forthe molar area, the force level ranges from216–847N, and for incisors from 108–299N.6

Clearly, in order for a ceramic to survive, it must be capable of resisting these stresses. As ageneral guide, in order for posterior restorationsto survive, they should be capable of withstand-ing a mean load of approximately 1000N.7

Also, as mentioned above, if a flawed ceramic isplaced in an aqueous milieu, it swells by imbib-ing water, which further degrades its fractureresistance.8

Dental ceramics

Dental ceramics are broadly divided into threecategories, silica-based, alumina-based and zirconia-based. All varieties, with different fa-brication processes, are used for intra- and extra-coronal dental restorations. Table 3.1 comparesmechanical properties, and Table 3.2 the fabri-cation processes of some popular all-ceramicsystems.

Figure 3.12 Catastrophic fracture of an all-ceramic crownon the maxillary right central incisor.

Figure 3.13 Catastrophic fracture of an all-ceramic crownon the maxillary right central incisor.

Definitions

� Fracture toughness – the resistance to fracture or crack propagation ismeasured as a material’s fracturetoughness, expressed as KIC. The latteris the measure of the amount of energyrequired to initiate a fracture. Thelarger the KIC value, the greater theforce required for initiating a fracture,or put another way, the more resistantthe material to fracture formation.Numerous methods are used to retardfracture within a ceramic material,including crack deflection, zoneshielding, contact shielding, crackbridging and phase transformation (forzirconia ceramics). Many of thesestrengthening and toughening mecha-nisms are utilised in a variety of contemporary dental ceramics, withvarying success, with the ultimate aimof increasing their fracture toughness9

� Modulus of elasticity (MOE) – measureof the elasticity or stiffness of a mate-rial. A low MOE (e.g. elastic band)implies greater flexibility and shock-absorbing capability, while a highMOE (e.g. porcelain) signifies brittle-ness and lower stress-handling ability


Silica-based ceramics

Feldspathic porcelains

Conventional, silica-based ceramics were the firsttypes of porcelains used for fabricating dentalrestorations. These materials are highly aesthetic

by mimicking natural dentition. The earliestmethod for fabricating all-ceramic inlays, ve-neers and crowns using feldspathic porcelainswas using either a platinum foil or refractorydies. Whilst more expedient techniques havesuperseded these methods, they still have a placein contemporary dentistry. For example, minimal

Table 3.1 Average mechanical properties of contemporary dental ceramics.10,11

Ceramic Flexural Fracture MOE Hardness (GPa)strength (MPa) toughness – KIC (GPa)

(MPam1/2)

Feldspathic porcelain 95 0.9 60 Greater than 6.5Empress 1 106–120 1.2–1.5 65 6.5Empress 2 306–400 2.8–3.5 105 5.3In-Ceram Spinell 238–377In-Ceram Alumina (slip) 594 4.4 265 11In-Ceram Alumina (dry-pressed) 440 3.1–4.6 265 11In-Ceram Zirconia (slip) 630 4.8–8 240 10.5In-Ceram Zirconia (dry-pressed) 476 4.9 240 11Procera alumina 450 (0.4mm coping) 4.5–6

to 687 (0.6mm coping)

DC-Zirkon (partially stabilised 680 5.5 240 13zirconia)

Procera AllZircon12 900–1200 9–10 Greater than 13

Table 3.2 Fabrication processes of some all-ceramic systems.

All-ceramic Platinum Refractory Lost wax Wax template Strengthening CAD/CAMsystem foil dies with milling mechanism

Feldspathic porcelain Yes Yes – Yes – –Empress 1 Yes – Dispersion CAD/CAMEmpress 2 Yes – Dispersion CAD/CAMIn-Ceram Alumina – Yes Infiltration –In-Ceram Zirconia – – Infiltration CAD/CAMProcera – – Densely CAD/CAM

sinteredCercon – Yes Phase CAM

transformationLava – Yes Phase CAM

transformationDC-Zirkon – Yes Phase CAM

transformation


tooth preparation requiring thin cross-sectionveneers (less than 0.5mm) are ideally fabricatedon platinum foil or refractory dies. Refractorydies are also utilised for porcelain inlays.

The major drawback with feldspathic por-celains is low flexural strength according to ISO 6872, predisposing to fracture, with poorlongevity.13 However, they still have a place in contemporary aesthetic dental procedures,including PLVs and inlays/onlays (Figs. 3.14 &3.15). However, due to inherent weakness, anadhesive technique using silane-coupling agentsand resin luting agents for cementation is manda-tory for gaining support from the underlyingtooth structure. In addition, meticulous attentionis necessary for tooth preparation, which should

accommodate a uniform thickness of porcelainfor PLVs (Figs. 3.16–3.19), and a minimum of 2mm for sufficient bulk for inlays/onlays.Finally, many of the high-strength ceramiccopings discussed below use silica-based porce-lain for the veneer overlay.

IPS-Empress 1 (leucite-reinforced glass ceramic)

The IPS-Empress system was conceived at theUniversity of Zurich, Switzerland in 1983, andcommercially marketed by Ivoclar Vivadent in1990.14 The material is essentially a feldspathicsilica-based ceramic, composed of 63% siliconedioxide and 19% aluminum oxide with the addi-

Figure 3.14 Cavity preparation for a feldspathic porcelaininlay in mandibular first molar.

Figure 3.15 Cementation of a feldspathic porcelain inlay inmandibular first molar.

Figure 3.16 Feldspathic PLV case study: pre-operative statusof maxillary centrals showing decay and worn, uneven edges.

Figure 3.17 Feldspathic PLV case study: following decayand composite fillings removal, depth-cutting burs are usedfor precise tooth preparation.


tion of leucite crystals to form a leucite-reinforced castable glass ceramic. The rationalefor its development was to eliminate or minimisemicroporosities created during the sintering ofall-ceramic materials.15 These voids predispose tofracture initiation; fractures grow and eventuallyresult in failure of the material. The incorpora-tion of leucite crystals creates barriers to crackgrowth, preventing microcracks and improvingflexural strength and fracture resistance by dis-persion strengthening. In addition, the injection-moulding process with heat and pressure reducesshrinkage and further enhances the flexuralstrength. The flexural strength ranges from95–180MPa, and fracture toughness (KIC) isapproximately 1.3MPam1/2.

Two methods are available for fabricatingEmpress 1 restorations. The first is using the lost-wax process, similar to that used for conven-tional porcelain fused to metal crowns. Theshape of the restoration is carved in wax and thepattern invested and heated in a furnace. Themould of the restoration is then injected with thedesired shade of an Empress ingot heated to1200°C. The heat and pressure ensure accurateadaptation and marginal integrity. Followingdivesting, the restoration is finished using eitherthe staining or the layering technique. Theformer is used for inlay/onlays by painting highchroma pigments for characterisation, followedby glazing to ‘seal’ the surface. The latter, layer-ing technique, is used for crowns and laminatesby veneering the pressed core with dentineand/or enamel porcelain.

The second method uses a computer-aideddesign/computer-aided manufacturing (CAD/CAM) process. Following tooth preparation, animpression is made or an intra-oral cameradirectly scans the cavity or crown preparation.Using appropriate software, the restoration isgraphically designed and relayed to a millingmachine, which cuts an Empress ingot to thedesired shape. Once again, either the staining orthe layering technique is used to complete therestoration.

Indications for Empress 1 are inlays/onlaysand anterior single unit crowns (Figs. 3.20–3.23). Empress 1 is unsuitable for stress-bearingteeth and multiple splinted units or fixed partialdentures (FPD). The endearing qualities ofEmpress 1 are superb aesthetics, excellent mar-ginal integrity and ease of fabrication. Further-more, being a silica-based ceramic, the intagliosurface can be etched with hydrofluoric acid andbonded using silane and an adhesive cementationprotocol. The ease of fabrication and the abilityto bond restorations have contributed to the clinical success of Empress 1, even though thematerial is mechanically inferior to other dentalceramics.

IPS-Empress 2 (lithium disilicate glass ceramic)

Empress 2 (Ivoclar-Vivadent) was released in1998, with superior mechanical properties com-

Figure 3.18 Feldspathic PLV case study: completed porce-lain laminate tooth preparation, with underlying tooth sub-strate of an acceptable colour.

Figure 3.19 Feldspathic PLV case study: post-operativestatus showing restitution of aesthetics.


pared with Empress 1, but without compromis-ing aesthetic qualities (Figs. 3.24–3.27). The flex-ural strength and KIC range from 340–400MPaand 2–3.3MPam1/2, respectively. The fabricationprocess is identical to Empress 1, although dif-ferent veneering porcelain (fluorapatite glassceramic) is necessary for the Empress 2. Due tothe mechanically stronger substructure, the man-ufacturer claims that gaining support from theunderlying tooth, via adhesive cementation is notmandatory. The major drawback with Empress2 is the extremely technique-sensitive laboratoryprotocol, which has resulted in numerous inci-

Figure 3.20 Empress 1 case study: pre-operative viewshowing discoloured, stained, heavily restored and chippedmaxillary central incisors.

Figure 3.21 Empress 1 case study: two indirectly castceramic post-cores cemented into roots of maxillary centralsto improve colour and light transmission of tooth.

Figure 3.22 Empress 1 case study: tooth preparation-to-definitive crown relationship.

Figure 3.23 Empress 1 case study: post-operative statusshowing two cemented Empress 1 crowns with improvedanterior aesthetics (laboratory work by David Korson,London).

Figure 3.24 Empress 2 case study: defective metal–ceramiccrowns on central incisors.


dences of de-lamination of the veneering porce-lain from the underlying core. Another concernis its recommended use for FPDs, requiring con-nector dimensions between abutment and ponticof 4mm × 4mm. This means that the gingivalembrasures should be of sufficient length withlong contact points, which may not be anatomi-cally possible, resulting in compromised peri-odontal health and poor aesthetics.

Alumina-based ceramics

In-Ceram Spinell (glass-infiltrated magnesium alumina)

In-Ceram Spinell (Vita) is twice as translucent asIn-Ceram Alumina, specifically intended to allowthe underlying natural tooth structure to ‘shinethough’ the material. Its use is primarily for indi-rectly fabricated inlays and onlays, assuming an acceptable colour of the underlying tooth,allowing the restoration to disappear within thenatural tooth. However, due to its reducedmechanical strength, In-Ceram Spinell is unsuit-able for posterior crowns, but is highly aestheticfor single anterior crowns.16

In-Ceram Alumina (glass-infiltrated alumina)

In-Ceram Alumina (Vita) is a partially sinteredporous alumina, which is subsequently infiltratedwith molten glass. The flexural strength and KIC, are 352–600MPa and 2.7–4.49MPam1/2,17

respectively, superior to both classes of Empress.Optically, alumina is denser than leucite glass,but still exhibits excellent aesthetics (Figs.3.28–3.31). Two methods for fabrication arepossible. The dry-pressed method uses pre-processed ingots, allowing milling with orwithout CAM/CAM software. The slip methoduses dispersed alumina in an aqueous solution,which is painted on to a specific plaster die. The laboratory process is protracted, involvingnumerous stages. To avoid de-lamination at thecore–veneer interface, caution is required toavoid air particle abrasion of the core prior toveneering.18

Figure 3.25 Empress 2 case study: tooth preparation-to-definitive crown relationship on soft tissue model.

Figure 3.26 Empress 2 case study: completed Empress 2crowns with correct lustre and texture.

Figure 3.27 Empress 2 case study: post-operative viewshowing aesthetic enhancement and gingival health aroundthe Empress 2 crowns on central incisors (laboratory work byGerald Ubassy, France).


Procera (pure densely sintered alumina)

To capitalise on the strength of alumina, the early1990s saw the introduction of a pure, denselysintered alumina (99.9% aluminum oxide) core,called Procera.19 The highly dense alumina pos-sesses minimal microporosities, reducing fracturepropagation, and improving mechanical pro-perties. The occlusal stress needed to break aProcera coping is around 1500N;20 even afterveneering with a low-fusing porcelain, such asAllCeram, the restorations still require a stress of1300N before fracture is imminent. As statedabove, the recommended force resistance forposterior restoration is 1000N. Therefore, aProcera coping is a suitable substructure for bothanterior and posterior prostheses. Althoughstrong, the aluminum oxide/low-fusing porcelaincomplex significantly reduces opposing naturaltooth wear to 60µm per annum, compared withfeldspathic porcelain, which has annual wearrates in the region of 230µm per annum.21

The fabrication process involves scanning acorrectly trimmed plaster die of the tooth prepa-ration (Figs. 3.32 & 3.33). Next, CAD/CAMsoftware is used to design the substructure, andthe digitised coping design is relayed via theInternet to Goteborg, Sweden or New Jersey,USA, where copings are manufactured in anindustrial quality-controlled process, and subse-quently returned to the ceramist. To compensatefor shrinkage during sintering, the exact shrink-

Figure 3.28 In-Ceram Alumina case study: defectivemetal–ceramic crown on left maxillary central incisor.

Figure 3.29 In-Ceram Alumina case study: tooth preparation.

Figure 3.30 In-Ceram Alumina case study: tooth prepara-tion-to-definitive crown relationship under ultra-violet illumination.

Figure 3.31 In-Ceram Alumina case study: cemented In-Ceram Alumina on left central incisor (laboratory work byPaul Sturridge, London).


age volume for each die is calculated, and anenlarged die is made to these dimensions to compensate for the anticipated contraction. The system offers a choice of coping thickness(0.25mm, 0.4mm or 0.6mm), opacity (white orstandard) and material (alumina or zirconia). Amarginal integrity of 70µm is achievable, withinclinical accepted norms of 50–100µm.22

The restoration is completed by veneering the coping with either silica- or alumina-basedporcelain (Nobel Rhondo). A major advantageof a Procera coping is its ability to mask under-lying tooth discolouration (Figs. 3.34 & 3.35).

Although translucent, allowing light transmis-sion to the underlying tooth, the coping densityis sufficient to conceal tooth discolouration or metallic cores.23 Procera is classified as a high-strength ceramic with a flexural strengthapproaching 700MPa, sufficient to support theweaker veneering porcelain, and obviating theneed for an adhesive cementation protocol. Thismay be potentially advantageous because avariety of luting agents can be utilised, includingzinc phosphate, glass ionomers and resin-modified glass ionomers (see Chapter 10).Finally, the longevity of Procera restorations is 7–10 years24, comparable to conventionalmetal–ceramic crowns (Figs. 3.36–3.39).

Figure 3.32 Correctly trimmed plaster die with a hollowapical to finish line, allowing clear margin delineation forscanning and manufacture of alumina coping via a CAD/CAMprocess (Procera, Nobel Biocare).

Figure 3.33 Correctly trimmed plaster die with a hollowapical to finish line, allowing clear margin delineation forscanning and manufacture of alumina coping via a CAD/CAMprocess (Procera, Nobel Biocare).

Figure 3.34 Discoloured right central incisor.

Figure 3.35 Masking ability of a ceramic core: the dis-colouration on the right central incisor is easily obscured bya Procera alumina coping.


Zirconia-based ceramics

The higher strength of zirconia, compared toalumina, is not solely related to phase transfor-mation toughening, but varies according to complete sintering, porosity and addition of stabilising yttria. Zirconia is the strongestceramic used in dentistry, and depending on aspecific product, the flexural strength can exceed1000MPa. Although anterior crowns are possi-ble, zirconia is primarily indicated for stress-bearing posterior crowns and FPDs (discussedbelow). Limitations of zirconia compared withalumina are poor light transmission (due toreduced glass content) and high value, result-ing in an almost metallic optical opacity andradiopacity. Therefore, in situations wheretranslucency is of paramount concern, forexample anterior aesthetics, alumina is moresuitable than a zirconia coping of comparablethickness.25

In-Ceram Zirconia

In-Ceram Zirconia (Vita) is a zirconia-reinforcedglass-infiltrated alumina, which is basically In-Ceram Alumina toughened by the addition of 33wt% of partially stabilised zirconia. As with In-Ceram Alumina, two methods of fabrication are available, slip or dry-pressed, and again, thelatter is thought to be mechanically superior due

Figure 3.36 Procera alumina case study: palatal erosion ofmaxillary left lateral and canine has resulted in thin, fragileand unaesthetic enamel.

Figure 3.37 Procera alumina case study: tooth preparationwith a chamfer finish line.

Figure 3.38 Procera alumina case study: two completedProcera crowns.

Figure 3.39 Procera alumina case study: cemented Proceracrowns with enhanced aesthetics, preventing further enamelerosion (laboratory work by Jean-Marc Etienne, France).


to pre-processing by a controlled industrialprocess.

Yttrium-stabilised zirconia

Examples of commercially available materialsinclude DC-Zirkon (Austenal), ProceraAllZirkon (Nobel Biocare), Cercon (Dentsply/Ceramco), Lava (3-M ESPE) and Cerec (Sirona).For densely sintered materials, shrinkage is themajor obstacle. This is circumvented by eithermilling a block of densely sintered material so that shrinkage is no longer a concern, or compensating for the anticipated dimensionalchanges. An example of a milling process is theDCS Precedent system (DCS Dental) that mills apre-sintered ceramic block, while some processescombine milling and sintering. The Cercon andLava methods use an enlarged framework of pre-sintered zirconia, which is milled and then fullysintered to the desired dimensions.

Longevity

Longevity of a restoration is the final aspect toconsider before choosing an all-ceramic system.When assessing longevity, the two most fre-quently used words are survival and successrates. These are not synonymous, but two dis-tinct evaluations. Survival rate implies that a par-ticular restoration is functioning, albeit withoutall the initial desired parameters. Success, on theother hand, implies that the restoration is notonly surviving but also successful, incorporatingall initial treatment objectives.26 For example, an all-ceramic bridge may fracture or de-laminate, but is nevertheless surviving. Whilst itis healthy and functioning, it lacks aesthetics (theHFA triad – see Chapter 2). A truly successfuloutcome is presence of all three entities: health,function and aesthetics.

The mode of fracture of all-ceramic singleunits differs from that of bridges (FPDs). Forcrowns, the weakest part is the intaglio or fittingsurface, which is subjected to the greatest tensileforces,27 creating flaws in the core substructure

eventually radiating to the veneering porcelainand causing de-lamination. Incorporating adense, high-strength ceramic core below theveneering porcelain therefore reduces flaws at theintaglio surface. For a FPD, stress distribution is concentrated at the connector sites, making these the weakest parts, which are vulnerable tofracture.28

Numerous laboratory and clinical data andanecdotes are available supporting use of all-ceramic restorations, but the real tests are con-trolled clinical trials, which are lacking for manyof the newer ceramic systems. It has been pro-posed that the minimal length of clinical trialsshould be 3–5 years, with a failure rate of lessthan 5%.29 Currently, systems that conform tothese broad guidelines are Empress 1, In-CeramAlumina and Procera, demonstrating good short-term clinical performance for single unit pros-theses.30

Metal–ceramic

Since their introduction in the 1960s,metal–ceramic crowns and bridges have shownremarkable clinical success. These restorationshave the longest clinical use, and their survivalrate is regarded as the gold standard, used as a guide for assessing success of all-ceramicsystems. Table 3.3 lists clinical studies on the longevity of metal–ceramic restorations.Although limited in their conclusions, these trialsact as a benchmark for evaluating all-ceramiclongevity rates, certainly over a short-termperiod.

Table 3.3 Metal–ceramic restoration longevity rates.

Study 5 years 10 years 15 years

Leempoel et al.31 95%Kerschbaum et al.32 92% 79%Walton33 97%Walton34 85%


Variations of metal–ceramic crowns, such asgalvano-ceramic systems, are also available asalternatives to conventional PFMs (porcelainfused to metal). However, long-term survivaldata is limited; a recent study claims success ratesranging from 92–96.5% after 7 years.35

Dicor and Cerestore

Dicor was the first castable all-ceramic system.Its indications, together with Cerestore crowns,were single anterior units. These systems gainedpopularity due to their simplified fabricationprocess using the lost wax technique, similar tometal–ceramic units. However, their reputationwas tarnished due to high clinical failures, occur-ring at either the cement–core or core–veneeringporcelain interfaces, and they are therefore cur-rently obsolete.36

IPS-Empress 1

Since its inception in 1990, Empress has becomea generic term for pressable ceramic restorations.Its success is due to ease of fabrication, by eitherthe lost wax process or CAD/CAM machines,producing precise and accurate restorations.Numerous short-term clinical trails havereported positive performance, but only withmeticulous clinical protocols and careful patientselection.37,38,39 The success rate of Empress 1crowns ranges from 92–99% for 3–3.5 years,with fracture as the primary cause of failure, fol-lowed by endodontic involvement and hypersen-sitivity.40 These figures are predominantly limitedto anterior crowns. A recent study over an 11-year period reports success rates of 98.92% foranterior crowns, but only 84.37% for posteriorunits, emphasising that Empress 1 crowns onposterior teeth are contraindicated.41

In-Ceram Alumina

This type of alumina ceramic, together withEmpress 1, is one of the longest surviving all-ceramic systems, and therefore its longevity is a

useful guide for assessing other systems. Over a6-year period, the success-to-failure ratio foranterior and posterior units is 98.9% to 1.1%,and 99.2% to 0.8%, respectively.42 The highsuccess rate for both regions is promising, indi-cating that In-Ceram Alumina is suitable forsingle-unit anterior and posterior crowns.

Procera

Procera is a bi-layer ceramic system, and frac-tures can either be superficial (limited to theveneering porcelain) or global (involving thecoping). The extent of the fracture determineswhether the ‘lesion’ is salvageable, or a replace-ment is necessary. Minor fractures, not affectinghealth or function, can be readily repaired withcomposite resin. However, larger de-laminations,accompanied by sharp edges encouraging foodimpaction, require a remake.

Numerous studies have reported varyingsuccess rates for the Procera system. In a multi-centre study over a 5-year period, the success rateranged from 94–97%,43 while in another studythe success was 97.7% for 5 years and 92.2%for 10 years.44 A recent study claims a 100%success rate after 5 years for anterior single units,and 95.15% for posterior crowns, averaging96.7% for all regions of the mouth.45 In an-other trial, Procera crowns over a 5-year periodshowed a success rate of 94%, and 87% of thepatients rated their restorations more than 7/10on an ordered analogue scale for aesthetics aswell as for function.46

Although it is difficult to make comparisionsof longevity reports from different studies, andbearing in mind a minimum success rate of 95%over 3–5 years, Table 3.4 shows success rates ofsingle units of some all-ceramic systems.

Ceramic bridges (FPDs)

Due to superior aesthetics, ceramic systems havebeen proposed for bridges, especially for anteriorregions of the mouth (Figs. 3.40–3.43). However,because of their relative infancy, the data aboutall-ceramic FPDs is confusing, depending on the


Table 3.4 Survival rates of single units of some all-ceramic systems.

System 3+ years 5+ years 10+ years

Empress 1 (anterior) 92–99% 98%Empress 1 (posterior) 84%In-Ceram Alumina (anterior) 99%In-Ceram Alumina (posterior) 99%Procera Alumina (anterior) 94–100% 92%Procera Alumina (posterior) 95%

Figure 3.40 Procera alumina FPD case study: pre-operativefacial view showing a worn, uneven incisal plane.

Figure 3.41 Procera alumina FPD case study: defective can-tilever bridge from left maxillary canine replacing missinglateral.

Figure 3.42 Procera alumina FPD case study: try-in ofProcera alumina, three-unit FPD substructure spanning fromleft central to canine, with lateral as pontic.

Figure 3.43 Procera alumina FPD case study: post-operativefacial view showing incisal plane parallel to curvature ofmandibular lip during a relaxed smile (laboratory work byJean-Marc Etienne, France).


experimental methodology and sparse clinicaltrials.

To select a particular ceramic for a specificclinical scenario, it is useful to compare long-term failure possibilities. Using an in vitromethod, such as finite element analysis, assessesstress distribution at a given load. This allowscomparison of different ceramics, with predic-tions for long-term resilience, which are valuablefor in vivo trials. Computational extrapolationof this data allows the calculation of a CARES/LIFE (Ceramic Analysis and Reliability Evalua-tion of Structure Life Prediction) index for timedependent reliability. With these methods, thelong-term fracture resistance of Empress 1, 2(Ivoclar-Vivadent, Schaan, Liechtenstein), In-Ceram Alumina (Vita, Bad Sackingen, Germany)and zirconia (3Y-PSZ zirconia, Metoxit, Thyangen, Switzerland) were evaluated. BothEmpress 1 and In-Ceram Alumina exhibited highfracture probabilities if used for posterior all-ceramic bridge substructures after a 10-yearperiod. The inference is, contrary to the manu-facturer’s claims, In-Ceram Alumina is unsuit-able for posterior FPDs. Empress 2 was morepromising, while zirconia showed the bestresults, with little fracture probability after 10years of simulated stresses.47

Besides material properties, another criticalfactor for preventing fractures of FPDs is thesurface area and design of the connectorsbetween abutments and pontics. Ideally, thelarger the surface area, the better the fractureresistance. However, if embrasure space islimited, large cross-section connectors areimpractical, conflicting with oral hygiene accessand/or aesthetics. This is particularly relevant forEmpress 2 FPDs, which require an occlucogingi-val connector height of 5.0mm (Figs. 3.44 &3.45).48 Since the core is stronger than theveneering porcelain, it may be prudent to leavea naked core at the tissue side of a connector forincreased strength.49 The opposing view is thatFPD fracture resistance increases after veneeringwith the overlying weaker porcelain due to astable bond between the two layers. Althoughmany all-ceramic cores exceed the averagethreshold masticatory forces, even on posteriorteeth,50 life expectancies are not identical to clini-

cal lifetimes as many factors are unaccounted for,such as the pulp, periodontal ligament or adhe-sive cement thickness.51

Probably the most promising ceramic for FPDsis zirconia, either infiltrated into an aluminamatrix (In-Ceram Zirconia), or partially sta-bilised with yttria (DC-Zirkon, DSC Dental/Vita). Stabilised zirconia has the capacity towithstand occlusal stresses of around 2500N,comparable to a conventional metal–ceramicFPD of similar dimensions. The main differencewith metal–ceramics is that fractures are super-ficial, limited to the veneering porcelain, whilefor zirconia the fractures are global, encompass-

Figure 3.44 Tooth preparation for all-ceramic Empress 2,three-unit FPD, spanning from maxillary right lateral to leftcentral with right central as pontic.

Figure 3.45 Try-in of Empress 2 substructure; notice theextremely long inciso-gingival connectors necessary forstrength and resilience.


ing the entire substructure, necessitating replace-ment of the entire prosthesis.52

Table 3.5 lists indications for choosing an all-ceramic system for a variety of clinical scenarios.Caution is necessary regarding all-ceramic FPDsuntil further clinical trials substantiate short- andlong-term longevity.

CLINICAL PRACTICE

The above discussion has illustrated that thesalient points regarding the choice of an all-ceramic system are its ability to withstandocclusal stresses and longevity. Fractures are themain cause of failure, occurring at any interfaceof the tooth/restoration complex including thefollowing:

� Dentine: cohesive failure due to poor toothpreparation design

� Dentine–cement: adhesive failure of the DBA

� Cement: cohesive failure due to poor com-pressive strength of luting agent, e.g. glassionomer (GI), resin-modified glass ionomer(RGI)

� Cement–ceramic core: adhesive failure, e.g.for Procera AllCeram, In-Ceram Zirconia,Dicor53

� Ceramic core: global failure for singlecrowns, initiating from the intaglio or fittingsurface, and connector sites for FPDs

� Core–veneer: de-lamination, especially forEmpress 2, Cerestore and In-Ceram Alumina

� Veneering porcelain: superficial fracturing orchipping due to inadequate support from thedense core. This is particularly significantwhen a uniform thickness ceramic core isfabricated of a tooth preparation with largeinter-arch or inter-abutment spaces, resultingin an unsupported veneering overlay. There-fore it is essential that the core has sufficientheight to support a uniform layer of theoverlying weaker porcelain. This is achievedby waxing a short tooth preparation to thecorrect height, before core fabrication. Withthe Procera system, this can be achieved by

Table 3.5 Indications for choosing an all-ceramic system.

All-ceramic system Inlays/ Veneers Ant. single Post. single Ant. FPD Post. FPD Masksonlays unit crowns unit crowns discoloured

tooth

Feldspathic porcelain Yes Yes Yes No No No NoEmpress 1 Yes Yes Yes No No No NoEmpress 2 Yes Yes Yes Yes1 Possible3 No YesIn-Ceram Spinell Yes No Yes No No No NoIn-Ceram Alumina No No Yes Yes1 Yes No YesProcera No Yes2 Yes Yes Yes No YesIn-Ceram Zirconia No No Yes4 Yes Yes4 Possible5 YesProcera Zirconia No No Yes4 Yes Yes4 Possible5 YesDC Zirkon No No Yes4 Yes Yes4 Possible5 YesCercon No No Yes4 Yes Yes4 Possible5 YesLava No No Yes4 Yes Yes4 Possible5 Yes

1 Absence of occlusal dysfunction.2 Mask pronounced discoloration, e.g. tetracycline staining or metal post/core.3 Depending on occlusion and available embrasure space for connectors.4 Depending on colour of adjacent dentition: zirconia is brighter (high value) and has less light transmission than alumina.5 Promising, but sparse short- or long-term clinical longevity data.


double scanning (inside–outside scanning) toensure that the core is of sufficient height tosupport the overlying porcelain.

References

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A thing that is not understood often becomes the focus of mystery, fear, indifference or abjectrejection. Colour, although a part of nearly everyhuman activity, is one of those things that ispoorly understood and shrouded by misconcep-tions. Much of the scientific literature on colouris riddled with mathematical formulae, which,useful in a technical or industrial laboratory,have little meaning to everyday situations. Thedental literature usually reports results of theparticular aspect of colour under scrutiny,without discussing fundamental principles. Theaim of this chapter is to ‘open the doors of perception’ so that the entire dental team cancomprehend and use colour in daily practice. Thefirst section deals with fundamental concepts,including definitions, measurements (both quantitative and qualitative), sensation and per-ception of colour. The second section explainsvariables influencing shade selection and how tocircumvent pitfalls during ocular assessment, andconcludes with digital colour devices for dentalshade analysis.


Sight is the spearhead of human senses. Visiontakes precedence over all other senses: hearing,smell, touch and taste. If there is a sensory con-flict between the senses, vision is the ultimatearbitrator, a phenomenon known as visualcapture. Colour vision is a part of the visualexperience and one of the most complex pro-cesses occurring in the brain. Colour realisationis the result of three processes: stimulation, sen-sation and perception. It is important to clarifythat these three processes are not synonyms todescribe the same event, but distinct sequentialevents occurring during colour detection. Anexplanation of colour involves many branches ofscience, including physics, chemistry, physiologyand psychology. The process by which radiantenergy (light) relates to a psychological experi-ence (colour) is termed psychophysics.

Colour perception involves the presence ofthree entities: a light source (illuminant), an

4Colour and shade analysis


object and a detector (ocular or instrumental).The preceding statement implies that all threeitems should be present before colour is per-ceived. This is not always necessary, and contraryto popular belief, it is possible to perceive colourwithout a stimulus or a sensation. Ultimately,colour experience is in the mind of the beholder,it is not an innate property of an object or theeyes (Fig. 4.1). Although an illuminant/object/detector does lead to colour perception, it isimportant to realise this is only one type ofcolour experience, known as conscious colourperception. Other types of colour experiences are subconscious colour perception, e.g. recallinga memory or dreaming,1 and paraconscious perception, e.g. during a psychedelic experienceunder the influence of hallucinatory drugs (inboth these states of mind, neither illuminant nor object is present to illicit a response). In thediscussion that follows, colour experience is confined to conscious colour perception.

The stimulus for colour

The first part of the stimulus/sensation/percep-tion triad is the physical stimulus of colour.Radiant energy (light) is a narrow band of theelectromagnetic spectrum, on the one extremecomprising long waves of radio broadcasting to

the other of shorter gamma radiation waves. Thevisual system of the eye is only capable of detect-ing wavelengths ranging from 380nm (violet) to780nm (red).2 According to Isaac Newton,3 lighthas no colour, it is only when it interacts with anobject that colour is produced. This was depictedin his famous experiment of splitting light by aprism into the colours of the visible spectrum,comprising red, orange, yellow, green, blue,indigo and violet (Fig. 4.2). As previously stated,the parts which comprise the stimulus for colourare the illuminant (light source), an object and adetector.

The illuminant

The quality of light is determined by its colourtemperature, measured in Kelvin (K); this variesfrom a cool blue sky (9000K) to candle light(2500K). In 1931, CIE (Commission Interna-tional de l’Éclairge or International Commissionon Illumination)4 recommended use of standardlight sources A, B, and C, which were supple-mented in 19715 to include illuminant D65. Theselight sources are distinguished by their spectralpower distribution curves and are utilised forcolour determination under specific conditions.For example, Standard Illuminant A representsincandescent light with a colour temperature of2856K, Standard Illuminant C is average day-

Figure 4.1 A glass sculpture illuminated by colours of thevisible spectrum as an allegorical illustration that colourexperience is in the mind of the beholder.

Figure 4.2 A variation of the seminal Isaac Newton experi-ment showing that a glass prism splits white light into coloursof the visible spectrum.

Colour and shade analysis 79

light at 6774K without ultraviolet radiation, andStandard Illuminant D65 is daylight at 6540Kincluding the wavelengths of ultraviolet radia-tion. A distinction is required between a sourceand an illuminant. To be precise, a source is aphysically realisable light (e.g. a dental operatinglight), an illuminant may or may not be realis-able, but if an illuminant is converted into aphysical form, it is then termed a standardsource. For the purpose of this discussion, theterms source and illuminant are interchangeable.The colour of an object appears differentdepending on the illuminant. This property oflight sources to influence the colour of objects istermed colour rendition (Figs. 4.3 & 4.4).

The object

Similar to a cube having three dimensions,length, width and depth, colour also possessesthree dimensions: value, hue and chroma. Thevalue is the quantity of light reflected by anobject compared to a pure white diffuser (reflect-ing 100%), and a black absorber (absorbing allincident light with no reflection). If a materialreflects most of the light falling on its surface, itappears bright, i.e. it has a high value. Con-versely, a dark object absorbs most of the inci-dent light and appears dull, i.e. has a low value.Between these two extremes is a gradation ofvalue termed the grey-scale. The tomato inFigure 4.5 shows a reflectance of 14%, comparedto the 100% white diffuser on the left, and a black absorber with 0% reflectance on theright.

The second dimension of colour is hue orwavelength of light; this is dependent on thespectral reflectance (of the visible spectrum) froman object. For example, Figure 4.6 shows thatwhen white light strikes the surface of a tomato(in this case separated into the colours of thespectrum for clarity), all colours are absorbedexpect red. The tomato therefore appears redbecause the spectral reflectance is limited only tothe red wavelength (i.e. the tomato reflects onlythe red part of the white light). An opaque ob-ject (such as the tomato) reflects a specific Figure 4.3 Incandescent illumination renders a yellow

appearance to this dentofacial composition.

Figure 4.4 Same image as Figure 4.3, but viewed by lightwith a colour temperature of 5600K (simulated daylight), pro-ducing a more realistic colour rendition.

Figure 4.5 The value of the white diffuser on the left is100%, and that of the black absorber on the right is 0%. Thetomato has a reflectance of 14%, reflecting only 14% of theincident light falling onto its surface.


wavelength of the visible spectrum and producesa spectral reflectance curve, while a transparentcoloured object (e.g. coloured glass) creates aspectral transmittance curve. A translucentobject, such as a tooth, produces both spectralreflectance and transmittance curves. These spec-tral curves are analogous to the power distribu-tion curves of illuminants.

Chroma is the last component of colour. Thethree peppers in Figure 4.7 have the same hue,but with an increasing colour intensity from leftto right. The pepper on the left is least saturatedand appears pale, i.e. it has a low chroma. Themiddle is more saturated, while the third on theright is the most saturated, having a vividappearance, with the highest chroma.

Colour is numerically quantified by its threedimensions: hue, value and chroma. Quantifyingcolour is similar to determining the dimensionsof an object, where a ruler is equivalent to acolour-measuring instrument (colorimeter orspectrophotometer), length to a colour space,and the scale, such as imperial (inches) or metric(metres) to colour co-ordinates of a specificcolour space. The two popular devices for objec-tive measurement of colour are the colorimeterand spectrophotometer. The colorimeter uses thetri-stimulus method, comprising three colouredfilters corresponding to selective spectral sensi-tivities to the three primary colours, red, greenand blue (Fig. 4.8). The readings X, Y and Z arethe amount of the three primary colours for agiven object, which are converted to a specifiedcolour space. The spectrophotometer, on theother hand, measures the spectral distribution(reflectance or transmittance) of an object ratherthan just three colours. This method is moredescriptive and is capable of ascertaining colourusing different illuminants. The readings of aspectrophotometer curves (spectral reflectance or transmittance) can either be plotted, or converted to colour co-ordinates for particularcolour spaces.6

Many colour spaces and co-ordinates areavailable to quantify colour, but for brevity, theMunsell7 and the CIEL*a*b* (1976), aredescribed. The benchmark is the Munsell System,conceived in 1905 by the American artist A.H.

Figure 4.6 A tomato appears red because it absorbs all thecolours of the visible spectrum (right side) except those in thered wavelength region (left side).

Figure 4.7 Three red peppers of the same hue [red] butvarying chroma (depth of colour) increasing from left to right.

Figure 4.8 Graphical representation of the three primarycolours: red, green and blue.


Munsell. This is fabricated from paper colourstrips corresponding to three colour co-ordinates: the Munsell Hue, Munsell Value andMunsell Chroma, and later modified to theMunsell Re-notation System.8,9 These systemsexpress a colour by a letter and number combi-nation according to the Munsell Colour Charts.This notation is also used for the Vitapan 3D-Master shade guide (Vita) (Fig. 4.9).

The initial CIE colour space introduced in1931 with the Yxy coordinates proved inade-quate because colours were represented only intwo dimensions (hue and chroma), and the per-ceived colours had no correlations to visual per-ception. In 1976, CIE modified their colour space

Figure 4.9 The Vitapan 3D-Master shade guide.

Figure 4.10 The CIE L*a*b* colourspace depicted by a sphere (image cour-tesy of Vita).

to the L*a*b*, where L* indicates lightness(value), and a* and b* are the chromaticity co-ordinates. The CIE L*a*b* colour space is bestvisualised using a sphere (Fig. 4.10). The verticalaxis representing L*, the top is white (value of100%) and the bottom black (value of 0%). Inthe a* direction, +a* corresponds to red, while -a* is the complementary colour green and forthe b* co-ordinate, +b* is yellow, and -b* denot-ing the complementary colour blue. Chroma isthe radial axis traversing from the centre to theperiphery of the sphere. The centre of the spherehas low chroma, and the periphery high chromacolours. The colour space representing naturalteeth is located between the +a* and +b* co-ordinates, in the red, red – yellow (orange) andyellow wavelengths of the spectrum (Fig. 4.11).

Sensation (the detector)

The third part of the stimulus for colour is thespectral response of the detector, in this case theeye. Visual sensation is a chemical, electrical andphysiological process. An elementary descriptionis conversion of physical energy (light) intoneural messages, a process termed transduction.

Radiant energy enters the eye via the corneaand is focused on to the retina by the lens. Thelens changes its curvature (accommodation) tofocus light rays through an aperture of the iris


known as the pupil. The black appearance of thepupil is attributed to the fact that most of thelight entering the eye is absorbed by light sensi-tive pigments in the retina10 (similar to lightfalling on a black surface). Visual acuity (sharp-ness) occurs at the centre of the lens where spher-ical and chromatic aberrations are negligible.

The retina is a mosaic of two types of photo-sensitive cells, called rods and cones (Fig. 4.12).The cones are responsible for chromatic vision,and contain photosensitive pigments with spec-tral sensitivities to the three primary colours,

corresponding to wavelengths 448nm (blue),528nm (green) and 567nm (red).11 When stimu-lated by light, the pigments undergo photode-composition to create an electrical impulse fornerve excitation. Most of the 6 million cones areclustered in the fovea, a depression in the retinawith a surface area of 1mm2 at the retina’scentral focal point (Fig. 4.13). The field of viewof the fovea is 2°, and moving peripherally, thecones mingle with rods. The cones have a directone-to-one neurone link, which accounts fortheir ability to convey precise information to theoptic nerve, resulting in sharp images.

The rods have a maximum distribution about20° from the fovea. Their photosensitive pigment(rhodopsin) has a maximum relative spectral sensitivity to only one wavelength of 510nm(green), resulting in achromatic vision. The rodshave no ‘hotline’ to the optic nerve and impulsesfrom a group of rods converge on to a singleneurone. An advantage of this neural arrange-ment is that rod vision is possible under dimlighting conditions, but the disadvantage is thatthe resulting image is blurred compared to thatof cone vision.

In dentistry, the rod and cone distribution ofthe retina is significant during shade determina-tion. The clinician should concentrate, or stareat the tooth and shade tab to assess hue andchroma which activates cone (chromatic) visionwithin the 2° foveal locus. To ascertain bright-ness (value), the observer needs to look aside in

Figure 4.12 Pictorial representation of rods and cones in theretina of the eye. The cones are responsible for chromaticvision, responding to one of the three primary colours, red,green or blue. The rods (in the background), are responsiblefor achromatic vision, lightness and darkness.

Figure 4.13 Colours of the visible spectrum converging ontothe fovea in the eye, where chromatic vision is feasible.

Figure 4.11 A natural tooth absorbs all the colours of thespectrum (right side) except those in the yellow, orange andred wavelengths (left side).


order to engage rod vision located at a 20° radiusfrom the foveal locus.

The difference threshold for colours in thehuman eye is low enough to discriminate 7million colour variations.12 There are two maintheories to explain colour vision. The first is theYoung–Helmholtz trichromatic theory, whichstipulates that the retina has three types of recep-tors, each sensitive to one of the three primarycolours, red, green, and blue (Fig. 4.14).13,14 Thisrelies on the additive mixtures on colours, forexample when red and green lights are mixed,yellow is produced. Most dichromatic colourblindness is an inability to distinguish reds andgreens, and affects 1 in 50 of the population,predominately men, since the defect is geneticallysex-linked. In dichromats however, yellow(mixture of red and green) is still discernible, afinding that is in direct conflict with the Young–Helmholtz theory. The limitation of the Young–Helmholtz theory is that it only explains colourreception at one site (the retina), and is termed asingle-stage theory.

Hering’s opponent-process theory proposesthat post-retinal analysis of visual informationoccurs en route to the brain. This further analy-sis comprises opponent colours, red–green, blue–yellow and white–black, e.g. some of the neu-rones are turned ‘on’ by yellow, but turned ‘off’by blue.15 This means that if a colour is detectedat a particular site of the retina, the opposing

colour cannot be detected at the same time, i.e.it is not possible to detect a yellowish-blue.Together, the Young–Helmholtz and Hering’stheories offer a better explanation of colour sen-sation, termed a multi-stage theory.16

Exploitation of the opponent-process theory indentistry can be used to resolve severely dis-coloured teeth using porcelain laminate veneers.Patients exhibiting tetracycline staining are oftenprescribed veneers with an opaque maskingporcelain to conceal the discolouration, resultingin artificial, high-value prostheses. To create amore natural appearance, veneers can be fabri-cated using porcelains with modifiers of a com-plementary colour to tooth discolouration. Inthis way post-retinal processing of the neuralinformation will counteract tooth discolorationby the porcelain veneers, e.g. an orange stainedtooth would require a green porcelain modifier(although not a true complement, it serves theintended aesthetic function in ceramics).17 Dentalluting cements also employ the same theory forimproving the colour of a translucent all-ceramicrestoration.

Synopsis of the stimulus for colour

The three items constituting the stimulus forcolour are the illuminant, the object and thedetector (eyes). Each forms a spectral curve: theilluminant is represented by a spectral power distribution curve, the object by its spectralreflectance (or transmittance) curve and the eyeby its spectral response curve. It is the productof these three curves that forms the stimulus forcolour, which in finally interpreted by the brain.The next part describes how the cerebral appa-ratus interprets and decodes this chromatic graffiti.

Perception

The psychological process of vision resides in the brain, involving decoding neural data fromthe eyes. Retinal information reaches the visual

Figure 4.14 A glass sculpture demonstrating the Young–Helmholtz trichromatic theory, which stipulates that the eyehas receptors for only the three primary colours, red, greenand blue.


cortex, situated in the occipital lobe, via the opticnerve by traversing the thalamus. During transit,the information is continuously processed untilit reaches the higher centres of the brain, com-prising the right and left cerebral hemispheres.The right eye relays information to the left hemi-sphere and vice versa (Fig. 4.15). The visualcortex is one of the major sites responsible forprocessing visual data, and is part of the cerebralcortex. Three-quarters of the cerebral cortex iscomprised of the association areas that interpret,integrate and act on information from thesensory organs. Cerebral information processingis a two-way conduit, bottom-up processingfrom the senses to the brain, and top-down pro-cessing from the brain to other parts of the body for eliciting a response in reaction to aninput.

The right and left cerebral hemispheresperform different analytical computations. In aright-handed individual, the left hemisphere is‘dominant’ and responsible for cognitive tasks.Although the right is regarded as the ‘minor’hemisphere, it boasts perceptual and visualspatial superiority. This means that if an imageis flashed to the right hemisphere, it is recognisedquicker than if flashed to the left hemisphere. A bundle of neural tissue called the corpus callosum, besides a physical link between the twohemispheres, is also an important communica-tion channel. If the latter is incised (e.g. in neuralsurgery to treat epilepsy), the brain sees anobject, but cannot recognise it. In an individual

whose corpus callosum is severed, the image inFigure 4.16 is perceived as shapes and colourswithout any significance. However, in a personwith an intact corpus callosum, the left hemi-sphere senses shapes and colours and relays thisinformation to the right hemisphere, which con-ceptually perceives the image as a surreal repre-sentation of the American flag.

The image formed on the retina by the ocularapparatus is incomplete. In fact the retina doesnot see the object as it appears, but rather a sym-bolic representation of it, which is termed animplicit representation. This image is a 21/2-dimensional sketch, more than two dimensionsbecause orientation is conveyed, but not three-dimensional because depth is not explicitly represented.18 The brain carries out complexcomputations, using past experiences (either its own or atavistic references), biases, etc. toconvert an image into a three-dimensionalexplicit representation.19 The mind is unaware ofthis computational aspect of visual conscious-ness, but responsive to its result.20

From the above, it is apparent why individu-als discern a particular colour differently. Addi-tionally, the brain perceives the world not as itis, but as our mind wants it to be. A clinician,during tooth shade analysis, is tainted by pastexperiences, which may not be identical to thoseof the patient or the ceramist. These conflicts areinevitable, but awareness of biases and idio-syncrasies prevents disagreements and avoids clinician/patient/ceramist conflicts.

Figure 4.15 Superior view of the human skull, showing thata light flashed to the right eye (yellow beam) is relayed to theleft visual cortex located in the occipital lobe and vice versafor the left eye (pink beam).

Figure 4.16 An individual with a severed corpus callosumcan not interpret this image of a tooth as a surreal represen-tation of the American flag.


Tooth colour determination

The variables affecting tooth colour determina-tion are broadly divided into:

� Physical� Physiological� Psychological� Dental

Physical variables

The illuminant

It is well established that the quality of illumi-nation affects colour perception, a phenomenonknown as colour rendition. In order to achievereliable and repeatable shade assessment, theillumination must be standardised with respectto quality and quantity. The light qualities mostconducive to colour discrimination are CloudDiffused North Noon Daylight, possessing auniform spectral power distribution21 with acolour temperature of 6500K22, CIE StandardIlluminant C or D65. The quantity or intensity oflight should be 1500 lux23, which is equivalentto four 220W fluorescent tubes at a distance of2 metres.24 Also, the light source should not bedirectional, but uniformly diffuse to avoid specular reflection.25 Many proprietary devicessatisfy these criteria, and their use is mandatoryto circumvent shade discrepancies.

Metamerism

The stimulus for colour is a product of spectralcurves belonging to the illuminant (spectralpower distribution), the object (spectral re-flectance or transmittance) and observer (spectralresponse). Metamerism is a phenomenon thatdescribes why the colour of a pair of objects isdifferently perceived when one factor is changed,while the other two remain constant. There aretwo types of metamerism: object and observermetamerism.

Object metamerism is the comparison of a pairof objects that have the same colour under agiven illuminant, but when the illuminant is

changed, their colours no longer match. This isbecause the objects have different spectralreflectance curves, but if they match for a givensource they must share the same colour co-ordinates (e.g. CIE tri-stimulus values).Thesetwo statements seem contradictory but are not;the reason is that a spectral reflectance curve contains more information than the colour co-ordinates derived from it. In order for twoobjects to match for any lighting condition, i.e.to be an invariant pair, their spectral reflectancecurves must be identical. The significance ofobject metamerism is that if a restoration (crownor filling) matches the surrounding or adjacentteeth under the halogen dental operating light, itmay not match when viewed by daylight (Figs.4.17 & 4.18). It is therefore advisable to performdental procedures using daylight-corrected illu-mination to avoid metamerism.26

Observer metamerism, either visual or instru-mental, is if the illuminant remains constant but the observer changes. In humans, this isdependent on the different physiological spectralresponse sensitivities of cones in the eyes. In den-tistry, this is manifested when a restoration isperceived to be a colour match by both patientand clinician, but not by the patient’s family and friends. To avoid this scenario, it is desirableto request that relatives or close friends accom-pany the patient during the shade assessingappointment.

Figure 4.17 Metamerism: a custom shade tab is a matchwith this patient’s dentition with flash illumination of colourtemperature 5500K.


The ambient environment

The context in which an object is viewed alsoinfluences its perceived colour, e.g. an object withbright surroundings will appear duller. Also,according to the opponent-process theory ofpost-retinal processing of visual information,looking at a red object will increase ocular sen-sitivity to green. Figure 4.19 demonstrates that atooth tab of the same shade is perceived differ-ently, depending on the coloured backdrop. Thedental surgery is a haven for a multitude ofcoloured items, including the interior decor,equipment, patient’s complexion, clothing and

cosmetic adornment, etc., with conflicting visualstimuli.27 It may therefore be necessary to createa chromatic microcosm with correct lightingwith an ideal background using a Munsellneutral grey N 7/0 card,28 and limit shade deter-mination to this designated area.

Physiological variables

In advancing years the lens of the eye diminishesits capacity to change shape (accommodate) withdiminishing focusing capabilities. Furthermore,cataract changes cause murkiness and yellowingof the lens. These degenerative processes causespherical and chromatic aberrations, with ‘yellowing’ of the vision.29 An affected operatortends to provide restorations that are yellower,which can be counteracted by allowing youngermembers of staff to participate in colour assessment.

If vision is not concentrated on the fovea ofthe eye, the location of the majority of cones, itis termed peripheral with a diminished ability todiscern colours. If this so-called indirect vision ismore than 40µm from the fovea, total colourblindness occurs. An operator who has constantdifficulty matching colours is advised to seek anoptician consultation to ascertain whether he/shesuffers with indirect vision.

Hue bias is differing tolerance for a specificcolour, an occupational hazard affecting dentistsand ceramists. The result is increased toleranceto yellow and reduced sensitivity to red (a colourrarely seen in natural teeth). Both dentist andceramist therefore demonstrate a red huebias.30,31 If a restoration has a mismatch with ared hue, it is more likely to be rejected than amismatch with a yellow hue. Clinical relevanceof hue bias is that a prosthodontist or ceramistmay consider a restoration as acceptable, but itmay be rejected by the patient as being tooyellow.

Psychological variables

Psychological variables are the most complexand least understood variables of colour realisa-

Figure 4.19 The context (background) influences the per-ceived colour of an object. All the shade tabs in this pictureare identical (Vitapan 3L1.5), but are perceived differentlydepending on the background colour. The correct shadeassessment is the tab with the neutral grey background.

Figure 4.18 Metamerism: the custom shade tab from Figure4.17 is too bright (high value) when viewed with daylight ofcolour temperature 6500K.


tion. Before describing cerebral processes specificto colour, it is necessary to outline basic func-tions of all sensory organs.

Stimulus detection

For a sense organ to detect a stimulus, the lattermust be of a minimum magnitude, termed anabsolute threshold, described by the signal detec-tion theory, which states when a signal isdetectable.32 An individual’s temperament greatlyinfluences whether or not a signal is detected,influenced by expectations, experience, motiva-tions, fatigue, the task at hand, time of day oreven regular exercise. Many inter- and intra-operator disagreements of a particular shade areattributed to these variables.

Discriminating two stimuli simultaneously, forexample matching a shade tab with a naturaltooth, involves a process called difference thresh-old or just noticeable difference (JND).33 Practi-cally, a minimum difference is necessary todiscern two different stimuli. This is the distinc-tion between what is a clinically acceptablecolour match, as opposed to what is a clinicallyperceptible colour match. The minimum colourdifference perceptible by the human eye rangesfrom ∆E* 0.3–0.5 (where ∆E* is colour differ-ence defined by CIE). However, acceptablethresholds are much higher at ∆E* 1.1–2.1,allowing greater latitude if restorations are notan absolute match with the surrounding denti-tion, but are nevertheless acceptable.

Adaptation

Sensory adaptation is diminished sensitivity by asense organ of a perpetual or unchanging stimu-lus. For example, one is not aware of the sensa-tion of wearing shoes throughout the day, freeingthe brain to concentrate on other stimuli. It canbe argued, if one stares at an object with un-divided attention, why it does not disappear?The reason for this is that eye quiver and regularblinking guarantee that the retinal image is con-tinually changing.

Another form of adaptation is the pheno-menon of chromatic adaptation or colour con-stancy. If a white card is viewed in sunlight and

then by indoor incandescent light, it is perceivedas white under both lighting conditions. This isone of the most enigmatic cerebral processes, andfurther endorses the fact that ultimately, it is the brain that ‘manufactures’ the perception ofcolour. The reason why the card maintains itschromatic status quo is that the brain ‘stores’ thecolour of the card in short-term memory, and,upon seeing the card for a second time (with a different colour temperature light source),recalls its initial memory of the card, and auto-matically assumes it is white. The technique toovercome this obstacle with shade assessment isas follows.

In order to detect a stimulus the image mustbe visible for a minimum of 60–70 millisec-onds.34 Below this minimum threshold, it isimpossible for the brain to interpret an image orits colour. Further exposure, up to a maximumof five seconds, is possible without the influenceof chromatic adaptation.35 This time intervalduring which colours can be accurately perceivedis called the chromatic assessment period (CAP).Shade determination should therefore be carriedout within the CAP. Concentrating on a tooth forprotracted periods, in the hope of gaining furtherchromatic information is futile and compromisesshade analysis.

Brightness or lightness constancy is similar tocolour constancy (chromatic adaptation), i.e. thebrain perceives the value of an object in relationto its context (background).36 In Figure 4.20 atooth of the same value appears lighter in frontof a black compared with a white background.The clinical relevance of brightness constancy isthat a tooth appears lighter with the darker oralcavity as the backdrop. To counteract this illu-sion, value determination should be performedwith a neutral grey background.

Dental variables

Tooth colour is not uniform across the populous,and even varies from tooth to tooth in a givenindividual. After the age of 35, teeth becomeincreasingly saturated with deeper chroma, especially in cervical regions. The value alsodecreases as the enamel overlay becomes more


translucent. Inter-arch differences include yel-lower maxillary anterior teeth compared to themandibular antagonists. An interesting variationis that the maxillary canines are redder thanthose in the mandible. Intra-arch differencesinclude lower value, yellower, and higher chromacanines compared to the adjacent incisors, whichhave the highest value of all teeth. These varia-tions should be borne in mind during extensiveprosthodontic treatment, especially when no sur-rounding teeth are present to act as reference orguides for the proposed prostheses.37

Shade matching of natural teeth to artificial prostheses

To obtain an absolute match (invariant match)for all illumination and viewing conditions, anatural tooth and artificial restoration must have identical physical properties and spectralreflectance curves. Matching materials of differ-ent compositions results in a close match, underlimited lighting and viewing conditions, which istermed a conditional match. Most visual shadedetermination in dentistry is a conditional matchthat is clinically acceptable (see above discussionon perceptibility vs. acceptability).

Multi-layered structure of natural and artificial teeth

The difficulty of dental shade selection is that theoperator has to negotiate a multi-layered struc-ture of varying thickness, opacities and opticalsurface characteristics. This introduces complex-ities far greater than assessing colour of a uni-formly turbid opaque object. Natural teeth, aswell as restorative materials that aim to emulatetheir structure, are multi-layered, which has animpact on the way they are perceived.

The basic hue of a tooth is determined by thecolour of underlying dentine, while value is aquality of the enamel overlay. Chroma is essen-tially the saturation of colour in dentine, but isinfluenced by the value and thickness of enamel.For accurate colour analysis, it is important tograsp the concept of visual interaction betweendentine and enamel. The following modelexplains how chromaticity of a tooth is affectedby its heterogeneous structure. The three dimen-sions of colour (hue, value, chroma) of a redpepper shown in Figure 4.21 can be gauged withrelative ease. The situation becomes complicatedwhen the red pepper is viewed through sheets ofglass of varying translucency. As translucency ofthe glass decreases its value increases, chromadecreases, but the hue is unchanged (Figs. 4.22& 4.23). The preceding analogy is identical tothe dual layering found in natural teeth, the redpepper representing dentine, and glass sheets the

Figure 4.20 Brightness or lightness constancy is demon-strated by placing a tooth tab of the same value (Vita Valuegroup 4), which appears brighter in front of a black (left), thanthe white (right) background.

Figure 4.21 The hue, value and chroma of the red chilli areclearly discernible when viewed without an optical barrier.


enamel overlay. Young dentition is characterisedby highly opaque, bright (high value) enamel,which obscures the underlying dentine. Inadvancing years the enamel becomes progres-sively more translucent and dull (low value),revealing the underlying dentine strata. Themulti-layered enamel/dentine is a major obstaclefor instrumental reading of tooth colour, sincethe value of enamel and its surface lustre oftencomplicate colour evaluation of the underlyingdentine.

Other optical variables influencing colour

Having established fundamentals of colour theo-ries, other optical variables influencing colourare fluorescence and opalescence, discussedbelow. Properties of dental porcelains includingchromatic reactivity and adaptability, opticalpurity and chromatic stability can be found else-where in texts dealing with dental materials.38

Fluorescence

Incandescence is the inherent ability of an object,animate or inanimate to emit visible light. Anexample of an incandescent creature is the glow-worm, while an artificial source is any householdbulb. Luminescence is the light emission from anobject other than that due to incandescence. Thisimplies that the object does not inherently emitlight, as with an incandescent entity, but anexternal light source is necessary to elicit anemission. Examples include luminescent roadsigns, which ‘glow’ when car headlights striketheir surface. Fluorescence is a particular type ofluminescence, described as visible light emissionfrom an object or surface in the presence of ultra-violet illumination. The degree of brightnessfrom a fluorescent object is often termed its lumi-nescent intensity.

Natural teeth have the capability to emitvisible light when exposed to ultraviolet light andtherefore exhibit fluorescence (Fig. 4.24).39 Irre-spective of their shade under white daylight,natural teeth fluoresce at a peak wavelength of450nm gradually decreasing to around 680nm.40

The salient point to note is that fluorescence ofteeth is independent of their perceived colourunder white light. This is a crucial factor duringmanufacturing of dental porcelains, whichendeavour to simulate optical characteristics ofnatural teeth. Ultraviolet light is not exclusivelylimited to nocturnal social venues such as clubsand discos, but is also prevalent in natural day-light. Since industrial pollutants are constantlydepleting the protective ozone layer, the amountof ultra-violet entering the atmosphere is everincreasing. Fluorescence makes teeth appearbrighter and whiter, and therefore alters their

Figure 4.22 A glass sheet is placed in front of the pepper inFigure 4.21, the chroma appears to decrease but its hueremains constant.

Figure 4.23 When a glass sheet of increasing opacity(decreasing translucency) is placed in front of the pepper inFigure 4.21, the chroma appears to decrease further still, butits hue remains constant. The increasing value of the glass (i.e.its brightness) is directly proportional to its increasing opacity.


visible colour under natural daylight. It is oftenstated that fluorescence is the property thatconfers vitality to natural teeth. The latter is oneof the culprits for apparent mismatching ofdental shade tabs with natural teeth. The reasonis that, although the visible colour of the toothcoincides with its porcelain analogue, the defini-tive restorations fails to harmonise with adjacentnatural counterparts due to different degrees offluorescence. The fault lies in the fact thatalthough a shade tab may match a given tooth,its fluorescence spectrum and luminescent inten-sity are dissimilar.

Opalescence

Radiant visible light contains photons rangingfrom 380–780nm. Certain materials, e.g. thesemi-precious opal gem, possess the ability totransmit and refract photons of larger wave-lengths, while reflecting or scattering photons ofa smaller wavelength. The result is that whenopalescent objects are viewed by incident whitelight a bluish appearance is apparent. Con-versely, when viewed by transmitted light theyappear orange–amber. Dental enamel also pos-sesses opalescence, and when viewed by incidentlight its appearance is bluish (Fig. 4.25), but bytransmitted light it glows with an orange–amberaura (Fig. 4.26). Similar to fluorescence, opticalpurity is also advantageous for emulating opales-cence with enamel porcelain.

Shade guides

Clinical conditions permitting, an ideal way toevaluate dentine hue and the enamel overlayindependently is to half prepare a tooth (Fig.4.27). This allows individual analysis of dentineand enamel as well as the thickness of each layer.This information is extremely valuable for theceramist to emulate both shade and thickness ofthe dentine and enamel porcelain layers of arestoration.

Figure 4.24 Natural teeth fluorescence when viewed byultraviolet illumination.

Figure 4.25 Opalescence: with reflected light, teeth have abluish tint (see incisal edge of right maxillary lateral incisor).

Figure 4.26 Opalescence: with transmitted light, teeth havea orange–amber aura (see incisal edges of maxillary centralincisors).


Types of shade guide

The most popular shade guides currently usedfor dental colour analysis are:

� Vita Classic (Vita, Bad Sackingen, Germany)� Vitapan 3D-Master (Vita)� Chomascop (Ivoclar-Vivadent, Schaan,

Liechtenstein)� Custom or specific chroma and value

guides

Vita shade guides

The ubiquitously used, and universally quotedshade guide is the Vita Classic, categorising hueswith the letters A (orange), B (yellow), C (yellow– grey) and D (orange – grey or brown). Withineach hue, the numbers are used to denote chromaand value. For example 1 is high value with lowchroma and 4 is low value with high chroma.This system of shade analysis, although inaccu-rate, is indelibly fixed in clinical and laboratorypractice.

In the early 1990s, Vita introduced the 3D-Master shade guide (Fig. 4.28), with the aim ofaccurately assessing shade according to the threecomponents of colour: hue, value and chroma.Unlike the majority of dental shade guides, the3D-Master attempts a three-dimensional analy-sis of tooth colour. The colour space occupied by

the guide is similar to natural dentition, betweenthe a* (red) and b* (yellow) colour co-ordinatesof the CIE L*a*b* system. The tabs are arrangedsystematically and logically, rather than ran-domly as in the Classic guide. Two 3D-Masterguides are available, Red and Blue, both fabri-cated from dental porcelains. The Red guide ismade purely of dentine porcelain, allowing accurate assessment of the basic dentine colour(Fig. 4.28), while the Blue incorporates cervicaland incisal porcelains for a more realistic repre-sentation of the multi-layers of natural teeth (Fig.4.29).

Figure 4.27 Half crown preparation on the left maxillarycentral incisor for independent assessment of dentine andenamel colour.

Figure 4.28 Facial view of patient with Vitapan 3D-Masterphotographed using light of 5500K.

Figure 4.29 The value groups in the Vitapan 3D-Master arenumbered 1 to 5 with all tabs within a group having the samevalue. The grey-scale in the background depicts decreasingvalue from left to right.


Vita Value, Vita Chroma and Vita Hue, simi-larly to the Munsell hue, value and chromacolour co-ordinates, represent the three dimen-sions of colour. The tabs are grouped into fivecategories, sequentially numbered, with anincreasing value (1, 2, 3, 4 and 5). All tabs withina value group have the same brightness (Fig.4.30). In a given value group, the chromaincreases from top to bottom (Fig. 4.31). Allgroups, with the exception of 1 and 5, are des-ignated three letters, L, M and R, correspondingto varying hue. For example L (light) is indica-tive of a yellow, M (medium) of a yellow–red ororange, and R (red) of a red hue (Fig. 4.32). Documentation for the 3D guide is analogous to

the Munsell Renotation System, comprising anumber/letter/number configuration. The firstnumber indicates the value group (1 to 5), theletter is the hue (L, M or R) and the secondnumber the chroma (1, 2 or 3). For example2M2 corresponds to the second value group, theM hue sub-group and a 2-chroma level. For anintermediate tooth shade, a combination of twotabs is used for the final colour prescription.

Chomascop guide

The Chomascop uses numbers to distinguishhue, e.g. 100 (white), 200 (yellow), 300 (orange),400 (grey) and 500 (brown). Chroma is indicatedby another set of numbers, 10 are high valuewith low chroma, while 40 is low value with highchroma (Fig. 4.33). This system is particularlyuseful when fabricating Empress restorations,since the Empress ingots correspond to theChomascop shade guide. A conversion chart isavailable to convert Chromascop shade tabs tothe Vita Classic shades.

Custom guides

Finally, if the tooth colour fails to concur withany of the shade guide tabs, porcelains can beused to fabricate a custom shade tab. If extremesof value and chroma are required, specificdetailed chroma and value guides are available

Figure 4.30 Shade matching using the Vitapan 3D-Masterguide. Step 1: ascertain the value group that corresponds tothe tooth. In the case illustrated, the value group of the max-illary central incisors = 2.

Figure 4.31 Shade matching using the Vitapan 3D-Masterguide. Step 2: using the M tab, the chroma = 2.

Figure 4.32 Shade matching using the Vitapan 3D-Masterguide. Step 3: select hue from the L, M or R tabs, here M ischosen to be the nearest match. The final shade prescriptionis written as 2M2.


(Figs. 4.34 & 4.35). These may be necessary withaged teeth of deep chroma, or youthful teethwith high values.

Limitations of shade guides

Limitations of shade guides are failure to accountfor the variability found in natural teeth:

� Degree of fluorescence41

� Degree of opalescence� Degree of enamel translucency42

� Enamel thickness (Fig. 4.36)� Enamel texture and lustre� Objectivity

Instrumental assessment

The main advantage of instrumental colourassessment is eliminating subjectivity. However,colour is not entirely an objective entity, and itsperception is heavily tainted by cerebral inter-pretation. Limitations of digital analysis havealready been mentioned in the colour theoriessection. Nevertheless, for comparative purposes,instrumental shade analysis is useful, and nodoubt will play a significant role in the future.43

Three basic types of device are used for instru-mental or digital shade analysis.

Figure 4.33 The Chomascop shade guide.

Figure 4.34 Accessory chroma and value shade tabs.

Figure 4.35 High chroma shade tabs.

Figure 4.36 Unlike enamel of natural teeth, the enamelthickness is uniform for all shade tabs in the Vitapan 3D-Master guide. The left tabs are sectioned in a sagittal plane,and the right in a mesial-distal plane.


Spectrophotometer

The most accurate device for colour analysis is a spectrophotometer, which produces spectralreflectance and/or transmission curves. The dis-advantages are complex technology, requiringextensive extrapolation of data, and high cost.Additionally, an object must be placed inside aspectrophotometer, which obviously presents adifficulty with natural teeth.

Proprietary products include SpectroShade(MHT Optic Research, Niederhasil, Switzerland)and Easyshade (Vita, Bad Sackingen, Germany).

Colorimeter

The colorimeter is based on the principles theYoung–Helmholtz theory of human vision,having ‘cells’ that are sensitive to the threeprimary colours. Whilst this method is not asaccurate as a spectrophotometer, the data is rel-atively easy to manipulate and user friendly.

Proprietary products include ShadeVision (X-Rite, Grandville, MI), ShadeEye NCC (Shofu,San Marcos, CA) and Digital Shade Guide(Rieth, Schorndorf, Germany).

Digital camera and red, green, blue(RGB) devices

The final, and probably the least accuratemethod is using a RGB or digital camera forcolour analysis. These devices analyse a captureddigital image for colour and chromatic mapping.Hence, software interpretation is heavily relianton the quality of the captured image, which isessentially the weak link. However, in theory,using high-quality glass optics with elaboratesensors, the analysis may be acceptable.

Proprietary products include ShadeScan(Cynovad, Montreal, Canada) and ikam (DCM,Leeds, UK).

CLINICAL PRACTICE

The aim of shade analysis is as follows:

(1) Record the basic dentine shade (hue), usuallyat the middle third of the tooth (pre-operative, prepared abutment and after fab-rication) (Figs. 4.37–4.39)

(2) Create a chromatic map showing colourvariations at the cervical (chroma), incisaland interproximal sites, together with thevalue of the overlying enamel (value) (Fig.4.40)

(3) Photographic documentation:� With different lighting to avoid

metamerism and assess fluorescence andopalescence (Figs. 4.41–4.42)

� Relative shade analysis with chosenshade tab

� Characterisations, such as cracks, stains,mamelons and surface texture and lustre

The above are achieved either visually or digitally.

Figure 4.37 Pre-operative shade analysis.


Ocular shade assessment

(1) The shade analysis appointment is sched-uled at the beginning of the day, when thedental team is not fatigued after a tiring dayin the clinic

(2) The ideal ambience should be tranquil andserene, devoid of distractions

(3) Perform shade analysis in presence ofceramist

(4) Ensure patient is accompanied by close rel-atives and friends to confirm chosen shade

Figure 4.38 Prepared abutment shade analysis.

Figure 4.39 Shade verification in dental laboratory duringcrown fabrication.

Figure 4.40 Drawing a chromatic chart for a central incisor(digital shade analysing machines automatically producechromatic mapping charts).

Figure 4.41 To avoid metamerism, carry out shade analysisusing daylight colour corrected illumination. The colour tabsappear yellowish with electronic flash.

Figure 4.42 To avoid metamerism, carry out shade analysisusing daylight colour corrected illumination. The same colourtabs as in Figure 4.41 now appear more realistic with day-light illumination.


(5) Ensure surgery surroundings are a neutralcolour or alternatively use a neutral greycard behind teeth and shade tabs

(6) Avoid lurid colour clothing and vivid cos-metics

(7) Moisten teeth, avoid dehydration of enamelor dentine

(8) Use colour-corrected daylight illuminationfor shade analysis

(9) To ascertain the value (brightness), lookaside to activate rod cells, located periph-erally to the fovea in the retina

(10) Record basic dentine shade at the middlethird of the tooth (hue and chroma) in lessthan 5 seconds (within CAP). Use differentshade guides as necessary

(11) Before repeating shade assessment, stare atblue card to avoid chromatic adaptation

(12) Create a chromatic chart of shade nuancesand characterisations

(13) Photograph teeth and tabs using differentlighting conditions, e.g. flash (5500K) and natural daylight (6500K), to mitigatemetamerism, and ultraviolet and transmit-ted light, for fluorescence and opalescence,respectively

(14) Photograph chosen shade tab(s) adjacent toteeth for relative shade analysis

(15) Photograph teeth at a 1 :1 scale for detailedcharacterisations

(16) Relay digitised images and chromatic mapvia e-mail to concerned parties (ceramist,specialist, patient).

Instrumental shade assessment

Follow steps (1)–(7) and (13)–(16). Substitutesteps (8)–(12) by following instructions for thechosen type of instrument for shade analysis.Depending on the type of instrument used, photographic documentation and creating achromatic map may not be necessary, since itmay be an integral part of the accompanyingsoftware.

References

1 Myers, D.G. (1998) Psychology. Worth Pub-lishers Inc., New York

2 Billmeyer, F.W. and Saltzman, M. (1981) Prin-ciples of Colour Technology. John Wiley &Sons Inc., New York

3 Newton, I. (1730) Opticks. Innys, London4 International Commission on Illumination.

(1931) Proceedings of the English Session,Cambridge, England. Bureau Central de laCIE

5 International Commission on Illumination.(1971) Colorimetry: Official recommenda-tions of the International Commission on Illumination. Publication No. 15 (E-1.3.1)Bureau Central de la CIE

6 Precise colour communication. (1994)Minolta handbook, Japan

7 Munsell, A.H. (1929) Munsell Book ofColour. Baltimore, Maryland

8 Newhall, S.M., Nickerson, D. and Judd, D.B.(1943) First Report of the OSA Subcommitteeon the Spacing of the Munsell Colours. J OptSoc Am, 33, 385–418

9 Munsell, A.H. (1961) A colour notation. 11thedn. Munsell Colour Co., Baltimore

10 Judd, D.B. and Wyszecki, G. (1975) Color inBusiness, Science and Industry. John Wiley &Sons Inc., New York

11 Marks, W.B., Dobelle W.H. and MacNicol Jr.E.F. (1964) Visual pigments of single primatecones. Science, 143, 1181–1183

12 Geldard, F.A. (1972) The human senses. 2ndedition. p.161. Wiley, New York

13 Young, T. (1807) ‘On the theory of light andcolours’, in: Lecturers in Natural Philosophy,Vol. 2, printed for Joseph Johnson, St Paul’sChurch Yard, by William Savage, London,p.163. ‘An account of some cases of the pro-duction of colours’, ibid., p. 634

14 Helmholtz, H von. (1852) Ueber die Theorieder zusammengesetzten Farben. Müller’s ArchAnat Physiol, 461; Poggendorff’s Ann, 87,45;Phil Mag, 4, 519

15 DeValois, R.L. and DeValois, K.K. (1975)Neural coding of color. In: Handbook of per-ception. Volume V: Seeing. Ed. Carterette E.C.


and Friedman M.P. p.162. New York Press,New York

16 Müller, G.E. (1930) Über die Farbenempfind-ungen. Z Psychol Ergänzungsb, 17 and 18

17 Yamada K. (1993) Porcelain laminate veneersfor discoloured teeth using complimen-tary colours. Int J Prosthodont, 6(3), 242–247

18 Jackendoff, R. (1987) Consciousness and thecomputational mind. MIT Press, BradfordBooks, Cambridge, MA

19 Churchland, P.S. and Sejnowski T.J. (1992)The computational brain. MIT Press, Bradford Books, Cambridge, MA

20 Crick, F. and Koch, C. (1995) Are we awareof neural activity in primary visual cortex?Nature, 375, 121–123

21 Panadent Limited (1983) Product informationon Waldmann Color-i-Dent lamps

22 Freedman, G. (1994) Color communication. JCosmet Dent, 60(8), 695–699

23 Burgt, T.P., ten Bosch J.J., Borsboom, P.C.F.and Kortsmit, W.J.P.M. (1990) A comparisonof new and conventional methods for quan-tification of teeth colour. J Prosthet Dent,63(2), 155–162

24 Photon Beard Limited, UK (1998) Photo-graphic lighting product catalogue

25 Seghi R.R. (1990) Effects of instrument-measuring geometry on colorimetric assess-ment of dental porcelains. J Dent Res, 69(5),1180–1183

26 Knispel, G. (1991) Factors affecting theprocess of colour matching restorative mate-rials to natural teeth. Quintessence Interna-tional, 22(7), 525–531

27 Johnson, W.M. and Kao, E.C. Assessment of appearance match by visual observationand clinical colorimetry. J Dent Res, 68(5),819–822

28 Goodkind, R.J., Keenan, K.M. andSchwabacher, W.B. (1985) A Comparison ofChromascan and spectrophotometric colormeasurements of 100 natural teeth. J ProsthetDent, 53(1), 105–109

29 Judd, D.B. and Wyszecki, G. (1975) Color inBusiness, Science and Industry. John Wiley &Sons Inc., New York

30 Kuehni, R.G. (1972) Color differences andobjective acceptability evaluation. J ColorAppearance, 1, 3–10

31 Douglas, R.D. and Brewer, J.D. (1998)Acceptability of shade difference in metalceramic crowns. J Prosthet Dent, 79, 254–260

32 Warm, J.S. and Dember, W.N. (1986) Awakeat the switch. Psychology Today, 149, 46–53

33 Myers, D.G. (1998) Psychology. Worth Pub-lishers Inc., New York

34 Crick, F. and Koch, C. (1997) The problem ofconsciousness. Scientific American Mysteriesof the Mind (reprinted from September, 1992issue), 19–26

35 Glick, K.L. (1995) Color management of cos-metic restorations. Curr Opin Cosmetic Dent,36–40

36 McBurney, D.H. and Collings V.B. (1984)Introduction to sensation and perception. 2ndedn. p. 194. Prentice-Hall, Englewood Cliffs,NJ

37 Goodkind, R.J. and Schwabacher, W.B.(1987) Use of a fibre-optic colorimeter for invivo colour measurements of 2830 anteriorteeth. J Prosthet Dent, 58(5), 535–542

38 Chu, S. and Ahmad, I. (2003) Light dynamicproperties of a synthetic low-fusing quartzglass-ceramic material. Pract Proced AesthetDent, 15(1), 49–56

39 Baran, G., O’Brian, W.J. and Tien, T.Y. (1977)Colored emission of rare earth ions in potas-sium feldspath glass. J Dent Res, 56,1323–1329

40 Monsenego, G., Burdairon, G. and Clerjaud,B. (1993) Fluorescence of dental porcelain. JProsthet Dent, 69, 106–113

41 Vanini, L. (1996) Light and color in anteriorcomposite restorations. Practical Periodontand Aesthet Dent, 8(7), 673–682

42 Davis, B.K., Aquilino, S.A., Lund, P.S., et al.(1992) Colorimetric evaluation of the effect ofporcelain opacity of the resultant color ofporcelain veneers. Int J Prosthodont, 5(2),130–136

43 Chu, S.J., Devigus, A. and Mieleszko, A.(2004) Fundamentals of colour: shade match-ing and communication in esthetic dentistry.Quintessence Publishing Co. Inc., Chicago

Introduction

Foundations (or cores) and intra-radicular sup-ports are platforms for the eventual definitiverestoration of structurally compromised teeth,either coronally mutilated vital teeth, orendodontically treated teeth requiring intra-radicular posts with a subsequent core build-up.

Before the type of foundation is chosen, it isimportant to remember that the strength of atooth is directly proportional to the quantity ofremaining enamel and dentine. Loss of toothstructure is attributed to caries, repeated replace-ment of failed restorations, fractures, endodon-tic access cavities and tooth preparation forextra-coronal restorations. Furthermore, endod-ontically treated teeth have a higher propensityto biomechanical failure because of increasedloss of tooth structure,1 increased brittleness dueto a reduced moisture content,2 and reduced pro-prioceptive response. The pressure threshold inroot-filled teeth increases by 57%, making thetooth less sensitive to occlusal loads, and hencepredisposed to fractures.3 Preserving as muchnatural enamel and dentine as possible is crucialfor the long-term survival of structurally com-promised teeth. Any procedure reducing the

amount of tooth, such as canal preparation for post placement, weakens rather thanstrengthens biomechanical capabilities.4 There isalso emerging debate whether or not a post is necessary,5 and if sufficient coronal dentine ispresent (more than half of the coronal toothstructure); placing a post only complicatesmatters, jeopardising the apical seal and struc-tural integrity. To recapitulate, the main purposeof foundations, with or without posts, is creat-ing a platform for the definitive restoration forattaining health, function and aesthetics (see theHFA triad in Chapter 2).

VITAL TEETH – SCIENTIFIC RATIONALE

Vital teeth

As stated above, the purpose of building foun-dations on structurally compromised vital teethis to support extra-coronal restorations. Repeat-edly replacing failed fillings leaves the residualtooth structure incapable of supporting furtherintra-coronal restorations, and in order to

5Foundations and intra-radicular support

Foundations and intra-radicular support 99

support an extra-coronal prosthesis, a core isrequired for adequate resistance and retention. Inaddition, the tooth is further weakened by con-tinual trauma of instrumentation, which shouldbe minimised to prevent endodontic involve-ment. The essential difference between cores onvital and non-vital teeth is that, in the former,retention is solely from coronal dentine, whilefor the latter, additional support is gained fromintra-radicular posts. A variety of methods isavailable for gaining retention on vital teethincluding pins, cavity modifications, dentinebonding agents (DBAs) and luting cements.

Retention

Pins

Pins have been advocated for generations as ameans of retaining cores on vital teeth (Fig. 5.1).The rationale is retaining as much of the remain-ing tooth structure as possible. However, pinshave numerous disadvantages, and their useshould be questioned in many clinical situations.6

Many studies have shown that pins cause dentine crazing and tooth fracture, and arepotentially perilous to the pulp and periodon-tium.7 Furthermore, no difference in retention isobserved with pins or other methods of sup-porting a core.8

Cavity modification

Instead of using pins, another method for reten-tion is modifying the remaining tooth structure.This includes creating undercuts, boxes, slots orgrooves for obtaining retention for the restora-tive material,9 particularly in conjunction withDBAs. The advantage is that the hazardous com-plications of pins are obviated. Nevertheless,placing retention features into dentine alsorequires careful judgement. The amount ofremaining tooth structure dictates whether slotsare possible without encroaching into the pulpor further compromising the structural integrityof the tooth. If teeth are excessively brokendown, crown lengthening or orthodontic extru-sion should be considered for ‘gaining’ extratooth structure. Cuspal coverage also helpsretention of the final restoration, and when thecusp width is less than 1mm, it should bereduced sufficiently to accommodate an appro-priate thickness of the overlying restorativematerial. For porcelain onlays, a minimum thick-ness of 2mm is required, together with adequateocclusal clearance (Figs. 5.2–5.4). Finally, incor-porating a ferrule effect in the final restoration is another method for additional retention forabsorbing functional stresses (see discussion onthe ferrule effect later in this Chapter). The termferrule means a bracelet or encompassing mate-rial. The ferrule of an extra-coronal restoration

Figure 5.1 Pins are one of the oldest methods for buildinga foundation on structurally compromised vital teeth.

Figure 5.2 Porcelain onlay case study: pre-operative viewshowing failing composite filling with secondary caries inmandibular first molar.


braces remaining dentine or the supragingivaltooth. It is the restorative material of the defini-tive restoration (usually metal or ceramic), whichcovers or encompasses residual dentine. A ferruleeffect is also used for a cast post/core with abuilt-in diaphragm or coping (Fig. 5.5).

Dentine bonding agents

Using DBAs with resin or amalgam coresincreases retention by enhancing bond strengthand reducing microleakage. The disadvantage isthe highly technique-sensitive and protractedclinical protocol. A detailed discussion of DBAsis found in Chapter 10.

Luting cements

Following the original concept by Baldwin in189710 of bonding amalgam to dentine with wetzinc phosphate cement, newer materials, such asglass ionomers (GIs) and resins, have been pro-posed using this method. At present, the efficacyand longevity of using GIs in a sandwich tech-nique with composite cores is debatable.11

Core materials

The choice of core material will profoundlyaffect survival of the ultimate restoration, and isdependent on whether a fill-in or build-up is nec-essary. A fill-in assumes that sufficient dentinearchitecture is present, and that the restorativematerial is used purely to fill voids, withoutacting as a supporting platform. When minimaldentine is available, a build-up acts as the plat-form for supporting the extra-coronal restora-tion. Therefore, a build-up requires greatermechanical resilience than a fill-in material. Thepopular materials include amalgam, GIs, resin-modified glass ionomers (RGIs) and resin com-posites with DBA. Table 5.1 summarises thesalient properties of fill-in and build-up restora-tive materials.

Figure 5.3 Porcelain onlay case study: preparation for indi-rect ceramic onlay, necessitating a minimum of 2mmocclusal clearance to accommodate a sufficient bulk ofporcelain.

Figure 5.4 Porcelain onlay case study: post-operative viewshowing cemented porcelain onlay.

Figure 5.5 Sectioned tooth with metal–ceramic crown,which incorporates a ‘bracelet’ or ferrule effect (apical toveneering porcelain) encircling or bracing the tooth toprovide additional strength.


For vital teeth, the direct technique is themethod of choice, using amalgam, resin com-posites, GI or RGI filling materials. DBAs in conjunction with resin composites and amalgamincrease retention while preserving the maximumamount of remaining tooth substrate. Amalgamhas long clinical success, and using amalgamadhesives further enhances its mechanical prop-erties (Fig. 5.6).

GIs offer direct adhesion to dentine and arecariostatic, but due to low tensile strength andresistance to fracture, are not recommended forareas of high occlusal stresses. Composite fillingmaterials are a better alternative, but are plaguedwith disadvantages of microleakage. Essentially,the linear thermal expansion of resin composites

Table 5.1 Materials for foundations (fill-in and build-up).

Properties Amalgam GI RGI Resincomposites

Strength High (in bulk, but Low Medium High (even in thin not thin sections) sections)

Seal By corrosion Adhesion to tooth Adhesion to tooth In conjunctionproducts and with DBADBA

Concerns Mercury Hydrophilic, Hydrophilic, Polymerisationcontroversy, crack formation crack formation shrinkage,electrolysis dimensionalinteraction with instabilitymetal prosthesis,patients withlichen planus

Technique Forgiving Intermediate Intermediate Sensitive

Retention Pins, cavity Cavity Cavity Cavitymodifications, modifications modifications modifications,DBA, cements DBA

Tooth preparation Delayed Delayed Delayed or Immediateimmediate

Indications Posterior teeth Fill-in, with Fill-in, with Anterior andbuild-up adequate dentine adequate dentine posterior teeth

architecture architecture build-up, flowablevarieties for fill-in,aestheticallysensitive areas

Figure 5.6 Amalgam core build-up.


is different from natural teeth, which causespost-operative sensitivity, pulpal pathosis andmicroleakage.12 However, recent advances inresin filling materials have resulted in physicalproperties equalling or surpassing those ofamalgam, including better handling, marginaladaptability, similar modulus of elasticity (MOE)and reduced annual rates of wear (Fig. 5.7).13 Tocircumvent microleakage, flowable compositesused as liners below composites offer superioraccessibility and adaptability for difficult cavityrecesses. The lower viscosity is beneficial forabsorbing polymerisation shrinkage stresses aswell as occlusal loads. A recent study assessingmicroleakage of teeth restored with intra-radicular posts, using different composite resinfilling material with and without a flowable composite liner, concludes that microleakage issubstantially reduced if a flowable compositeliner is used prior to building the core with eithera microhybrid or packable composite.14

VITAL TEETH – CLINICAL PRACTICE

Pre-assessment for cores on vital teeth

Before proceeding to build-up or fill-in struc-turally compromised vital teeth, the followingitems should be considered.

Radiographic evaluation

A radiograph will reveal the amount of residualtooth, decay, quality and extent of any existingfilling, periodontal and endodontic status. Inaddition, appreciation of pulp and root(s)anatomy will prevent inadvertent perforation ofthe pulp chambers, root furcations and concavi-ties. These findings will dictate whether the resid-ual tooth, following removal of the offendingfilling and decay, is capable of supporting a corebuild-up with retention boxes and grooves. Vital-ity should also be verified, especially if the toothhas been subjected to repeated trauma of replac-ing defective fillings. If non-vitality is suspected,root canal therapy at this stage is prudent, ratherthan waiting for the inevitable after fitting thedefinitive restoration. Furthermore, placing anintra-radicular support will offer additionalretention in cases of limited tooth substrate. Inthe presence of periapical or periodontal pathol-ogy, a build-up may not be feasible, without firstcarrying out root canal therapy or surgical crownlengthening.

Intra-oral evaluation

A careful examination, with transillumination,will reveal tooth and/or existing filling(s) frac-tures. Minor fractures may be salvageable, butextensive or deep vertical root fractures usuallyrequire extraction. The occlusion is also assessed,especially the inter-occlusal clearance for accom-modating the build-up and final restoration. Ifthe clinical crown height is insufficient, surgicalcrown lengthening or orthodontic extrusion maybe considered.

Clinical sequalae for cores on vital teeth

If, following the above evaluation, a core is prac-tical, the clinical protocol is as follows:

(1) Isolate tooth with rubber dam (Hint 5.1)(2) Remove exiting filling(s), decay and reduce

cusps that are either fractured (or display

Figure 5.7 Composite resin filling core build-up.


fractures lines), or less than 1mm in crosssection

(3) Assess remaining tooth substrate for eitherfill-in, or build-up with retention by strate-gic placement of retentive boxes, groovesand pins (Hint 5.2)

(4) If necessary, place suitable matrix band andwedges for supporting the core material

(5) Select fill-in or build-up material accordingto Table 5.1

(6) Follow manufacturer’s instructions for thechosen restorative material

(7) Remove rubber dam (Hint 5.3)(8) Carry out immediate or delayed tooth

preparation (depending on the material) forthe coronal restoration (Hint 5.4)

(10) Fabricate a chairside therapeutic tempo-rary restoration, before making an impres-sion for the definitive restoration (seeChapter 7)

NON-VITAL TEETH – SCIENTIFIC RATIONALE

For endodontically compromised teeth, thepurpose of intra-radicular anchorage is support-ing a core build-up, which in turn supports theeventual coronal restoration.

Post materials

The literature is ambiguous regarding the idealchoice of post/core materials for a given clinicalscenario, reporting varying survival ratesdepending on data derived from in vitro studies.The clinical factors, such as quantity of residualtooth structure, ferrule effect and occlusalstresses (especially non-axial), exert greater influ-ence on the survival rate than the material fromwhich a post is fabricated. Furthermore, thequality and precision of the definitive restorationis paramount for ultimate success of the tooth/restorative complex.15

Casting alloys

Custom posts are indirectly fabricated in thedental laboratory by the lost wax process usingcasting alloys. The existing root canal morphol-ogy dictates the length and cross-section geome-try of the cast post. These passive posts are welladapted, preserving existing root canal shape,necessitating minimum shaping or modificationwith rotary instruments. The rationale is to fab-ricate a post to fit the root canal, as opposed toshaping the root canal to fit a preformed post(Fig. 5.8). The advantages include retainingresidual tooth structure, unified post and coremade of the same material, with long-term clin-ical use.16 The disadvantages are a two-visit pro-cedure, increased clinical time, laboratory costs,fabrication of a chairside temporary post andcore, increased likelihood of bacterial contami-nation of post canal while awaiting cast postfrom the dental laboratory, and poor aesthe-tics if the definitive prosthesis is all-ceramic.Finally, corrosion by-products may elicit aller-gic reactions and cause root and soft tissue discolouration.

Prefabricated metal

Prefabricated posts are manufactured from dif-ferent metals, such as stainless steel, titanium,etc., with unique serrations, surface roughness

Figure 5.8 Indirectly cast gold post and core in left maxil-lary lateral incisor.


and cross-section geometry (tapered and/or parallel) for increasing retention (Fig. 5.9). Theadvantages include a single-visit procedure, lesschance of contaminating the root canal with oral fluids as post placement is performed at thesame time as root filling with rubber dam in situ, a core can be built using amalgam or tooth-coloured composite filling materials forimproved light transmission and aesthetics. Thedisadvantages include dentine removal to accom-modate the prefabricated shape, and conflictbetween ensuring a patent apical seal (minimum4–5mm) and sufficient post length for support-ing the final restoration.

Proprietary products include ParaPost(Coltene/Whaledent, New Jersey, USA) or Den-tatus Steel Posts (Dentatus, Hagersten, Sweden).

Ceramics

Ceramic varieties, such as zirconia and aluminaposts, offer improved aesthetics and high frac-ture resistance. The prefabricated ceramic postsare either a pure ceramic, or ceramics combinedwith synthetic plastics. Zirconia varieties areavailable as smooth, tapered and parallel, ortapering at apex and parallel at the coronalaspect (Fig. 5.10). They are rounded at the apicalzenith to minimise stress concentration at theroot apex. Other varieties include polyester with65% zirconium fibres, with lower MOE and

stiffness compared with pure zirconia, butwithout compromising the advantageous lighttransmission properties.17 Ceramic posts can beused with both the direct and indirect techniques,are highly biocompatible, radiopaque, and haveexcellent light transmission via both the root andcoronal restoration. The success rates of zirconiaposts are presently questionable, one studyshows similar survival to cast posts18, whileanother shows significantly lower survival whensubjected to intermittent forces compared tocarbon posts.19 In addition, zirconia posts arestiff, with a high fracture resistance, but shouldthe post fracture within the apical third of thecanal, salvage is often challenging or impossible.The alumina varieties are indirectly fabricated,creating a unified post/core complex using amilling machine.

Proprietary products include:

� Zirconia – CosmoPost (Ivoclar-Vivadent,Schaan, Liechtenstein), ER-Cerapost (Brasseler, USA)

� Alumina – Celay (Mikrona)� Polyester with zirconia – Snowlight

(Carbotech)

Fibre

Three types of fibres are used for dental posts:carbon, quartz or glass. Either the fibres are

Figure 5.9 Pre-fabricated titanium post with serrations forincreased retention with luting agent.

Figure 5.10 Zirconia posts in maxillary central incisors.


embedded in a resin matrix, or pliable non-impregnated strands are luted with resin cements(Ribbond, Seattle, USA) (Fig. 5.11). Table 5.2lists some common fibre posts, together withtheir mechanical properties.

Carbon fibre posts are biocompatible, resistantto fatigue and corrosion, have lower MOE com-pared with metals and are more conducive torepair. The reason for this is that fracture usuallyoccurs at the post/core interface rather than inthe root. Furthermore, numerous studies haveverified that the success rate of carbon fibre postsis comparable to that of cast post and cores overa 2–3-year period.20 The disadvantages are poorlight transmission, dark colour, lack of adhesionto resin luting agents and radiolucency.21 Thedark colour of carbon fibre posts has beenresolved by coating with a quartz layer toimprove colour (AesthetiPost, Bisco), and if usedjudicially, neither the fracture resistance nor aes-thetics are compromised in combination withdirect composite cores.22

Glass and quartz fibre posts offer improvedlight transmission, stain resistance, superior aes-thetics, and improved adhesion with resin-basedluting agents compared to the carbon fibre posts(Figs. 5.12 and 5.13). The MOE is similar, butnot the same as that of natural tooth structure,which minimises transmission of traumaticforces to surrounding dentine. The drawback, aswith carbon fibre, is the high radiolucency.

Table 5.2 Fibre posts.

Type of fibre Modulus of elasticity (GPa) Flexural strength (MPa) Proprietary product

Carbon 145 1500 Composipost RTD, Saint-Egreve, FranceQuartz 46 1400 Light-Post, RTDQuartz 40 890 Luscent Anchors, DentatusGlass 45 1390 Postec, Ivoclar-VivadentGlass 29 990 ParaPost Fibre White, Coltene-Whaledent

Figure 5.11 Pliable fibre (Ribbond, Seattle, USA) being usedas an intra-radicular support in an eccentric shaped root canalfor an eventual composite core build-up.


Criteria for intra-radicular post selection

Ideally, a post should conform to the three-dimensional shape of a root canal, withoutexcessive pre-shaping. The physical, mechanicaland optical properties should be similar tonatural tooth structure, and the post should forma hermetic seal with the existing dentine for alasting bond. In reality, none of the currentlyavailable post systems meets all these ideal crite-ria; a compromise is usually necessary for somebeneficial properties, while sacrificing others.The ultimate success or survival rate of anypost/core system is judged by its longevity. A

recent study concludes that the type of post andcore is irrelevant with respect to survival, theoverriding factor which influences longevity isthe amount of residual dentine height afterpreparation (ferrule effect).23 Other studies havealso reinforced the concept of retaining themaximum amount of internal and external toothstructure as the utmost important factor whenrestoring endodontically treated teeth.24

Currently, there is a lack of consensus in thedental literature for choosing an ideal post forintra-radicular support. Data and conclusionsfrom different studies are conflicting, and choiceis often dictated by prevailing clinical necessitiesand operator experience. However, it is impor-tant to understand the factors that influencethese choices, and the discussion below endeav-ours to elucidate advantages and limitations forreaching an informed judgement.

Coronal dentine and the ferrule effect

According to Milot and Stein, ‘if sufficient toothstructure is preserved, post selection has little orno effect on resistance to root fracture’,25 the ulti-mate survival of the restorative/tooth complex isdictated by the quality of the definitive restora-tion; an opinion which has been subsequentlyverified by numerous studies. However, in situa-tions when insufficient dentine is present for the ferrule effect, or factors such as aesthetics or multiple root canals prevail, the choice of post becomes significant.26 The ferule effect is the most significant aspect for survival of thepost/core complex, and at least 1.5mm ofcoronal dentine is recommended for a favourableprognosis (Fig. 5.14).27

Tapered vs. parallel

Tapered posts offer the advantage of conservingtooth structure near the apex due to their conicaldesign. The disadvantages are decreased reten-tion and pronounced wedging stresses at theapical part of the root canal, predisposing to cat-astrophic and unsalvageable fractures.28 Parallelposts offer superior retention, at the expense of

Figure 5.12 Quartz fibre posts (Luscent Anchors, Dentatus)posts for intra-radicular support in maxillary anterior teeth.

Figure 5.13 Glass fibre posts (ParaPost Fibre White, Coltene-Whaledent) with plastic rings for precise lengthmeasurements.


greater tooth removal to accommodate a cylin-drical geometry. This is especially perilous withtapering root apices and thin-walled root canals.The posts should ideally mimic the canal shape,placing minimum stress on the surroundingdentine.29 To achieve this objective, some manu-facturers have a combined taper and paralleldesign, e.g. a taper at the apical third and paral-lel for the remaining coronal two-thirds.

Smooth vs. serrated

The rationale for surface roughening or serra-tions is to increase micromechanical retention, orlocking effect, between the luting agent andradicular dentine. On the negative side, if re-treatment is required, removing a highly reten-tive post becomes a challenge. Conversely, asmooth surface helps post retrievability, but has less retention, and increases the chance ofdislodgement.

Passive vs. active

Metallic threaded posts (Dentatus Steel Posts,Dentatus, Hagersten, Sweden) are used forseverely broken-down teeth with the aim ofachieving maximum retention compared topassive, non-threaded varieties. The major

disadvantage of threaded designs is inducingstresses, which further weaken the already fragileand reduced radicular dentine, resulting in ele-vated failure rates. Due to this reason, threadedposts should be used with extreme caution. Fur-thermore, if retention is severely compromiseddue to a short root, a decision regarding the long-term survival of the tooth is necessary prior tousing a threaded post system.

Direct vs. indirect technique

The advantage of the direct approach is a single-visit procedure, reducing contamination of theroot canal with oral fluids during post place-ment, ideally at the same time as root filling with a rubber dam in situ. A direct procedurealso allows a wide choice of post materials;metal, ceramic and fibres. The cores can be builtusing either amalgam or a composite filling material. For anterior teeth, the direct techniquerequires a minimum 1.5mm height and width ofcoronal dentine for a ferrule effect, and for pos-terior teeth 2mm of coronal dentine or a deeppulp chamber. A prerequisite for ceramic posts,e.g. zirconia, is ensuring a ferrule effect of 2–3mm to prevent root and post fracture, espe-cially with a composite core (Fig. 5.14).30 Theferrule effect is particularly relevant when usinga resin core, which is mechanically inferior, andrequires surrounding dentine for resistingocclusal loads. The canal morphology should beconducive to the preformed post, requiringminimum shaping to preserve intra-radiculardentine. The direct technique is also expedientfor molar teeth with divergent roots, as a singlepath of insertion is not necessary as for the indi-rect technique.

The indications for an indirect technique arecases when there is excessive loss of coronaltooth structure and elliptical or flared canalsunable to accommodate prefabricated postgeometry without further canal shaping. Theindirect technique is also useful if an abutment is part of the foundation for a final FPD or telescopic prosthesis, necessitating a change inthe path of insertion for the final prosthesis.Additionally, a unified cast post/core complex

Figure 5.14 Zirconia post in left maxillary central with suf-ficient coronal dentine for the ferrule effect. The residualdentine should be sufficient to encircle or brace the post forsupport.


minimises material interfaces and is beneficial forabsorbing predominantly shear stresses.

There are two approaches for the indirect tech-nique. The first is making a direct template orpattern of the canal and core build-up on the prepared abutment, using an auto- polymerisingacrylic resin (Pattern Resin, GC). This pattern is either cast in metal, or milled with ceramics.A ceramic post/core complex is milled usingceramic ingots (usually alumina) in a millingmachine (Mikrona). Upon delivery, the surface is sandblasted and cemented with a resin lutingagent. This method produces a unified ceramicmonobloc post/core complex.

The second approach is shaping of the rootcanal to accommodate a prefabricated post(metal or ceramic), making an impression for theceramist to fabricate a wax pattern of the corein the dental laboratory, which is subsequentlyconverted into either metal or ceramic. If thecanal is enlarged or elliptical, it is filled withflowable composites to alter the shape foraccommodating a prefabricated post (LuminexPosts, Dentatus). For the indirect ceramic coretechnique, leucite glass is pressed on to a zirco-nia post in the dental laboratory and thepost/core complex cemented using an adhesivetechnique. Using factory-silanated zirconia postsfurther enhances adhesion with resin cements(Figs. 5.15–5.21). Some studies have reported

Figure 5.15 Indirect zirconia post–ceramic core case study:pre-operative status of two defective PLVs on root-filled, mis-aligned central incisors. Notice the gingival cleft on the rightcentral, and the excessive lustre on PLVs compared to tex-tured surfaces of natural lateral incisors.

Figure 5.16 Indirect zirconia post–ceramic core case study:impressions of two zirconia posts used for intra-radicularsupport and to pseudo re-align maxillary centrals.

Figure 5.17 Indirect zirconia post–ceramic core case study:Empress 1 cores pressed on to zirconia Cosmoposts (Ivoclar-Vivadent, Liechtenstein) in dental laboratory.

Figure 5.18 Indirect zirconia post-ceramic core case study:completed all-ceramic post/core complex.


Single- vs. multi-rooted teeth

For single-rooted teeth, either a direct or an indi-rect technique is possible. The choice is dictatedby whether the canal morphology is suitable fora prefabricated post, and the remaining coronaldentine is adequate for a ferrule effect. If thecanal shape is erratic, with minimal residualdentine, an indirect approach or filling the canalwith flowable composites is required. Multi-rooted teeth present difficulties for an indirecttechnique due to divergent roots, making a singlepath of insertion problematic. In these circum-stances, a direct technique is favoured, assumingadequate coronal dentine and pulp chamberdepth to support a chairside core.

Choice of luting agents

Similar to choosing a luting agent for crowns, theselection of cement depends on the post material(see Chapter 10). Additionally, when lutingposts, the following cement properties are desir-able:

� Dual or auto-cured for complete polymerisation

� Low viscosity for minimum cement thickness(this may be deleterious if prefabricated

Figure 5.19 Indirect zirconia post–ceramic core case study:cemented ceramic post/core complex with clearly discerniblemargins for final all-ceramic crowns.

Figure 5.20 Indirect zirconia post–ceramic core case study:fabrication of two Procera alumina (Nobel Biocare, Sweden)crowns. Notice incisal translucency and incisal edge stainingincorporated into veneering porcelain.

Figure 5.21 Indirect zirconia post–ceramic core case study:cemented Procera crowns showing impeccable integrationwith natural adjacent lateral incisors with respect to colour,texture and morphology and a healthy surrounding peri-odontium (laboratory work by John Hubbard, UK).

superior fracture resistance of zirconia posts withlaboratory-pressed leucite cores, compared withchairside composite cores,31 while others reportlittle difference. This affirms the notion thatusing a direct technique does not compromise thebiomechanical properties, while having advan-tages of expediency, less canal contaminationand reduced number of steps compared to fabri-cating a direct wax pattern or impressions, temporary post, investing and casting, which allincrease the chances for introducing errors.32


posts are luted in flared canals, resulting ina thick cement layer prone to breakdown).For flared canals, it is prudent to shape thecanal with a flowable composite prior tocementing the prefabricated post (LuminexPosts, Dentatus)

� High mechanical strength to resist stresses� Fluoride release and cariostatic� Radiopaque (especially when using carbon

and fibre posts to delineate post on radiographs)

� Achieves a chemical bond between dentineand post material (at both cement–dentineand cement–post interfaces)

Aesthetics

If an all-ceramic restoration is chosen as thedefinitive final prosthesis, particularly in aesthet-ically sensitive areas of the mouth, masking dis-colouration of the underlying tooth is of crucialconcern.

Tooth discolouration is categorised as superfi-cial, extrinsic or intrinsic. Superficial discoloura-tion is temporary stains from food dyes, tobaccoand alcohol, readily removed by prophylacticmeasures. Extrinsic blemishes confined to theenamel layer include hypoplasia (white or brownspots, patches and surface pitting), fluorosis(mottling) and ageing (increases enamel perme-ability33 with yellowish tints). In addition,erosion, abrasion and attrition also expedite discolouration. Intrinsic discolouration involvesthe deeper dentine layer resulting from trauma,tetracycline or sequelae of endodontic therapy.Leaching of metallic fillings (e.g. amalgam) orcorrosion by-products of casting alloys of previ-ous intra-radicular posts or prostheses alsocauses intrinsic staining.

There are four basic ways to obscure tooth discolouration:

� Alter the colour of the tooth substrate� Mask or neutralise staining by a luting agent� Mask or neutralise staining, either with

a ceramic core or a definitive all-ceramicrestoration by using porcelain opaquers or

complementary coloured porcelains to neu-tralise underlying discoloured dentine

� Using all-ceramic prostheses with a denseceramic core, e.g. Empress 2, Procera or zir-conia substructures

The above methods can be used either alone,or in combination, depending on the clinical sce-nario and prevailing profundity of the dis-colouration. It must be emphasised at the outsetthat all these methods are unquantifiable. Eachcase is assessed individually according to thedegree and extent of discolouration, clinicianand patient expectations, and using a trial anderror protocol until the desired result is achieved.

The present discussion is limited to altering thecolour of the tooth substrate, methods for whichinclude microabrasion, bleaching and light-transmitting intra-radicular posts. Microabra-sion is limited to superficial, isolated stains, whilebleaching is for extrinsic and intrinsic dis-colourations, and useful for both vital as well asnon-vital teeth. The drawbacks of bleaching areits ephemeral nature, and possible root resorp-tion for endodontically treated teeth.34 For root-filled teeth, light transmitting white fibre,ceramic or zirconia posts35,36 brighten the rootand tooth core,37 while metallic posts, if usedwith highly translucent ceramics (feldspathic andleucite glass), may be visible and detrimental toaesthetics (Figs. 5.22 & 5.23). Whilst metal postsoffer excellent mechanical properties, they lack

Figure 5.22 Sectioned incisor with a cast metal post andcore showing that the latter impedes light transmission to thesurrounding root.


light transmission and diffusion, often resultingin gingival shadowing at the cervical margins.

The optical behaviour of all-ceramic restora-tions depends on three factors:

� Relative degree of translucency or opacity ofthe all-ceramic system. Feldspathic or leuciteceramics (Empress I) are highly translucent,necessitating that the tooth substrate is anacceptable colour for optimal aesthetics.Alumina and zirconia ceramics are opticallydense, offering increased masking capabili-ties but with reduced translucency

� The luting agent. Many studies have statedthat the colour of an all-ceramic restorationis due to the intrinsic porcelain layering, andless dependent on the shade of the lutingagent.38 However, high chroma satins orbleach shades can alter shade with highlytranslucent ceramics

� Colour of tooth abutment or core. Veneer-ing a cast gold post/core with opaque anddentine porcelains masks the metal, andapproximates the colour of the core to thenatural abutment. While the core colour maybe acceptable, this method poses two prob-lems. Firstly, the opaque porcelain is highlyreflective, rarely seen in the natural denti-tion, resulting in a high value and artificialappearance. Secondly, the metallic substruc-

ture prevents light transmission via the root,and therefore compromises aesthetics of anall-ceramic crown

Figures 5.24–5.36 show a case study using allthree above methods to mask heavily discolouredmaxillary incisors. Table 5.3 summarises postmaterials and criteria for selection.

Figure 5.23 Same tooth as Figure 5.22 with an all-ceramicpost/core complex, which brightens the root by allowing lighttransmission.

Figure 5.24 Case study, masking discolouration with light-transmitting posts and all-ceramic crowns: pre-operativestatus showing discoloured centrals with defective ceramicrestorations on lateral incisors. All incisors were root filledfollowing a bicycle accident.

Figure 5.25 Case study, masking discolouration with light-transmitting posts and all-ceramic crowns: pre-operativestatus showing discoloured centrals with defective ceramicrestorations on lateral incisors. All incisors were root filledfollowing a bicycle accident.


Figure 5.26 Case study, masking discolouration with light-transmitting posts and all-ceramic crowns: glass fibre postsfor intra-radicular support and light transmission to brightenroots.

Figure 5.27 Case study, masking discolouration with light-transmitting posts and all-ceramic crowns: completed toothpreparations after cementing and trimming posts.

Figure 5.28 Case study, masking discolouration with light-transmitting posts and all-ceramic crowns: shade analysiswith 5500K illumination (flash) with Vita Classic shade guide.

Figure 5.29 Case study, masking discolouration with light-transmitting posts and all-ceramic crowns: shade analysiswith 6500K illumination (daylight) with Vita Classic shadeguide.

Figure 5.30 Case study, masking discolouration with light-transmitting posts and all-ceramic crowns: definitive impres-sion with additional silicone material.

Figure 5.31 Case study, masking discolouration with light-transmitting posts and all-ceramic crowns: definitive crowns-to-tooth preparations relationship.


Types of cores

When choosing the material for the core, the fun-damental principle is minimising material inter-faces. This means that the fewer materials usedin the post/core complex, the superior the finalbiomechanical properties. Similar material willcause less stress than disparate materials, reducemicroleakage and increase the potential to with-stand intra-oral loads. This is the rationale forusing an indirect technique, because the post/core complex is a single material entity. Thisprinciple is also applicable to all components ofthe post/core/definitive restoration complex, by forming a monobloc structure, which is

Figure 5.32 Case study, masking discolouration with light-transmitting posts and all-ceramic crowns: palatal aspect oftooth preparation showing adequate cingulum reduction toaccommodate sufficient porcelain bulk.

Figure 5.33 Case study, masking discolouration with light-transmitting posts and all-ceramic crowns: four completedEmpress 2 crowns with dense ceramic core to mask tooth discolouration.

Figure 5.34 Case study, masking discolouration with light-transmitting posts and all-ceramic crowns: post-operativestatus showing crowns cemented with a bleach shade resinluting agent to improve colour, and further mask underlyingtooth discolouration.

Figure 5.35 Case study, masking discolouration with light-transmitting posts and all-ceramic crowns: pre-operativedentofacial view of uneven incisal plane.

Figure 5.36 Case study, masking discolouration with light-transmitting posts and all-ceramic crowns: post-operativedentofacial view with incisal plane parallel to curvature ofmandibular lip.


conducive for resisting stresses. With a directtechnique, the material interfaces are increased,e.g. a prefabricated post, bonding agent and thecore build-up material.

Numerous materials are available for corebuild-ups, which have been previously discussedfor building vital teeth. When building cores on non-vital, endodontically treated teeth, twofurther aspects require consideration. Firstly itmust be ensured that the root canal filling is notcompromised during post placement. This is par-ticularly significant since periapical pathology ismore frequent with post-treated than with root-filled teeth.39 Microleakage can potentially occurat all stages of post placement, including canalpreparation, temporarisation and cementation.Secondly, the intra-radicular support furthercomplicates matters. Ideally, a chemical bond isdesirable between the post and dentine for pre-venting microbial ingress into the post canal.

Using contemporary dental cements, a chemicalbond is achievable at the cement–post interface,but the weakest link is the cement–dentine interface (see Chapter 10). The failure of thecement–dentine interface causes microleakage,leading to saliva and bacterial contamination,loss of retention (dislodgement) or ultimatelyroot fracture.

Modes of failure

Most prosthodontic failures are caused byfatigue fractures of one or more components of the restorative/tooth complex, including therestoration, abutment, core, post and lutingcement. Each component is subjected to non-axial occlusal function stresses causing fatigue

Table 5.3 Criteria for post selection.

Selection criteria Casting alloys Metals Ceramic Fibre

Shape Bespoke Tapered, parallel Tapered, parallel Tapered, parallel

Surface roughness Sandblasted Unique geometry/ Smooth/sandblasted/ Smooth, unique geometrythreaded silanised

Passive/active Passive Both Passive Passive

Technique Indirect Direct and indirect Direct and indirect Direct

Root configuration Single, possibly Single/multiple Single Single/multiplemultiple

Ferrule effect Desirable Desirable Essential for direct Essentialtechnique

Luting agent ZP1, GI, RGI, DR2 ZP1, GI, RGI, DR2 with DBA, GI, RGI, DR2 with DBAwith DBA, SAAR3 DR2 with DBA, SAAR3

SAAR3

Aesthetics Poor/average Average Excellent Average/excellent

Clinical time Protracted Expedient/protracted Expedient/protracted Expedient

Tooth preparation Delayed Delayed or Delayed or ImmediateImmediate Immediate

1 zinc phosphate.2 dual-polymerisation resins.3 self-adhesive auto-polymerisation resins.


fractures at the weakest point either of therestorative/tooth complex, or at the point ofmaximum stress. The fundamental principle forreconstructive procedures, especially of struc-turally compromised teeth, is to minimise non-axial (horizontal) stresses on the final pros-thesis.40 For intra-radicular supported teeth, thethree main factors predisposing to failure are:

� The thin, weakened root dentine walls sur-rounding the post that are incapable of with-standing stresses

� Compromised retention due to a reducedsurface area, leading to cement failure

� Fracture of the post itself41

To summarise, the three modes of failures42 inorder of increasing severity are:

� Loss of retention (most frequent) – salvageable

� Post fracture (less frequent) – possibly salvageable

� Root fracture – rarely salvageable

The above three can occur concurrently, butare discussed separately to elucidate thecausative factors.

Loss of retention

Dislodgement of a post is due to loss of reten-tion, and may be salvageable in isolation, butrarely in conjunction with root fractures. Theobjective is therefore to achieve maximum postretention, while mitigating risk of root fractures.Retention depends on numerous factors, such as post surface texture (and serrations), length,diameter, geometric design, timing of core prepa-ration for the final crown and choice of lutingagent. Active threaded posts offer the greatestretention, albeit at a price. Indenting the dentinewith grooves obviously enhances retention, butalso causes stresses that predispose to root fracture. Threaded posts should be used withcaution, and if retention is severely compro-mised, placing a post should be questioned forthe long-term survival of the tooth.

Any surface roughening, such as serrations orother unique surface topography, increases reten-

tion, irrespective of the post material or lutingcement.43 This is also true for cast posts withoutserrations, which exhibit less retention than ser-rated prefabricated posts.44 Due to this fact, andwhen canal morphology is satisfactory, passiveserrated prefabricated posts are an ideal choicefor maximum retention. Conversely, zirconiaceramic posts offer less retention because of theirsmooth surface texture.

The type of cement also influences the reten-tion of posts. Conventional cements, such as zincphosphate, rely on mechanically interlockingsurface irregularities of the root canal and posttexture, while GIs and resins adhere by bothmechanical and chemical bonds. The highestbond strength is achieved with resin cements,especially when pre-treatment of the post canaland post is incorporated with an adhesive cemen-tation protocol (see Chapter 10). The positivepoints of resins are higher retention and resist-ance to fracture, reinforcing thin dentine canalwalls and a MOE similar to natural tooth struc-ture. However, the negative factors are unwantedpolymerisation shrinkage stresses, microleakagefrom lateral canals and a demanding clinicaltechnique.

It is well documented that ultrasonic anddental handpiece vibrations cause breakdown ofthe cement film between the post and surround-ing dentine. Indeed, ultrasonic instrumentation isa method advocated for failed post removal.45

This is particularly relevant to cast post andcores cemented with zinc phosphate cement,whose core should be shaped during fabrication,minimising preparation once luted to preventdissolution of the cement film. Preparation of the core for the eventual crown within one hourof cementation has detrimental effects on reten-tion, and should be delayed at least 24 hourspost-cementation.46

Post fractures

Post fractures may occur in isolation or concur-rently with root fractures. The important pointabout isolated post fractures is retrievability.This depends on the location of the fracture andthe material of the post. Coronal fractures may


be salvageable, but deeply located fractures inthe proximity of the root apex are difficult toretrieve, due to diminished accessibility andsmaller root cross-section. The material fromwhich the post is fabricated also influenceswhether or not a post is retrievable. Materials,in order of ease of retrievability are fibre, metaland zirconia.

Root fractures

Root fractures are probably the most seriousconsequence of intra-radicular support, oftennecessitating extraction. During function, theleast stress is concentrated within the root canalwhile the maximum is at the circumference. Thelater is the reason for incorporating a ferruledesign into the definitive crown to reinforce thecircumference of the root. The ferrule effect, foran extra-coronal restoration, is 1–2mm cir-cumference embracing sound cervical toothstructure.

To mitigate root fractures, the first point toconsider is whether the chosen post will preventor predispose to fractures. If two materials of different mechanical properties are united, stressis concentrated in the weaker material. This isapparent with metal, carbon fibre and zirconiaposts, which are mechanically stronger thannatural tooth structure. After loading, theweaker dentine yields, resulting in root fracture.The rationale of many newer fibre posts, whoseMOE approaches that of natural tooth structure,is that deflection under load is of a similar mag-nitude to dentine and enamel, thereby minimis-ing root flexion (Table 5.4).47

Posts fabricated from titanium and zirconiahave a higher MOE and are stiffer than glass orquartz fibre, which have a lower MOE,approaching that of natural tooth, and are moreelastic for absorbing and dissipating occlusalforces. The material of a post influences whetheror not repair is feasible. A recent study states thattitanium and zirconia posts cause catastrophicfractures at the root apices, necessitating extrac-tion. Conversely, teeth restored with glass andquartz fibre posts exhibit coronal fractures, moreamenable to repair.48

There are two opposing views regarding thestiffness of posts.49 The first is that a post shouldpossess mechanical properties similar to dentine,so that flexion is identical, thus reducing chancesof root fracture. With an elastic post (low MOE),the tooth, post and cement all deform with asimilar magnitude during function. Breakdownof the weakest point, the dentine–cement–postinterface, results in dislodgement due to loss ofretention, microleakage and eventual fracture of the post or core. Many studies have reportedless likelihood of root fractures with elastic as opposed to stiff posts. However, followingcementation of the definitive crown incorporat-ing a ferrule effect, the difference between stiffand elastic posts is negligible.50

The second opinion advocates a highly stiffmaterial (high MOE), mechanically exceedingnatural tooth to withstand loads, and therebyminimise fracture. The concept is that a stiff postwill dissipate forces along the post into the rootcanal and fracture occurs after a longer period.51

The conclusions from the two conflicting ideasare as follows:

� With elastic posts, failure occurs within ashorter period, but is salvageable

� With stiff posts failure is delayed but is cat-astrophic and unsalvageable

The last item concerning root fractures is the type of cement. As well as offering superior

Table 5.4 MOE of different materials.

Material Modulus of elasticity (GPa)

Epoxy resin 4Dentine 15Composite resin filling 16Glass fibre 40Enamel 50Type III gold alloy 85Titanium 110Zirconia 210Carbon fibre 75–215Chrome cobalt 220


retention, resin-based cements have a MOEsimilar to that of natural teeth. Hence, the cyclicdeformation of resins is similar to that of dentineand enamel, with better shock-absorbing capa-bilities compared to conventional zinc phosphatecements.52

Pre-post placement assessment

In a similar vain to post selection, there is also alack of established protocol for clinical tech-niques for post placement. However, beforeplacing an intra-radicular support, the followingpreliminary assessment is essential to eliminatefactors that may compromise long-term survival.

Endodontic factors

The starting point is radiographic assessmentensuring that the tooth is symptomless with asound apical root filling and absence of periapi-cal pathology. Radiographs also allow evaluationof root morphology, number, shape and width of canals, iatrogenic lateral perforations or mis-alignment of previous posts. The post lengthshould be as long as possible for maximum reten-tion (at least the length of the coronal restora-tion), but with at least 4–5mm of apical rootfilling to ensure an adequate seal (Fig. 5.37). Ifthe crown-to-root ratio, in addition to sufficientroot filling length is not feasible, crown length-ening or orthodontic extrusion should be considered. The choice between surgery andorthodontics is determined by the gingival widthand contour, especially in aesthetically sensitiveareas of the mouth. Both procedures are notwithout problems, including an eventual lowercrown-to-root ratio, insufficient dentine of 1.5mm for the ferrule effect and compromisedaesthetics. The ideal diameter of a post is alsodebatable, but as a general guideline, the postwidth should be no greater than one third of theroot diameter at the corresponding depth.53

Finally, to prevent contamination of the canal(s),the time interval between the root filling and post

placement should be minimal, or they should beperformed concurrently.

Periodontal factors

Placing a post in an endodontically treated toothplaces further stresses, and the alveolar housingshould be capable of withstanding these addi-tional forces.54 As a generalisation, at least halfof the post length should be placed in a root sur-rounded by crestal bone. If bone loss, followingperiodontal destruction, is substantial, wedgingforces of the post with inadequate alveolarsupport may predispose to root fracture.

Figure 5.37 Radiograph showing two zirconia posts incentral incisors with adequate (at least 4–5mm) apical rootfilling.


Choice of definitive restoration

Before deciding on intra-radicular anchorage(post/core), it is necessary to decide on the typeof definitive crown. This is particularly signifi-cant if an all-ceramic prosthesis is considered,making the choice of the post and core crucial.Many all-ceramic systems are translucent (felds-pathic and leucite), requiring the post/corecomplex to be light transmitting and of a satis-factory colour to avoid aesthetic disappointment,while others (alumina and zirconia) are opticallydenser with acceptable masking capabilities.

Remaining coronal dentine

If possible, the crown preparation should becarried out prior to post placement. This allowsclear visualisation of the amount of residualcoronal dentine (Fig. 5.38). If inadequate coronaldentine is present, an indirect post/core may beappropriate. Alternatively, if the dentine height isgreater than 1.5mm, sufficient for the ferruleeffect, a direct technique is possible. For a directcomposite core, especially when using zirconiaposts, the ferrule effect is essential for resistingshear forces on anterior teeth. On posteriorteeth, the depth and height of the pulp chamberevaluation will indicate whether a direct core isfeasible.

Tooth location

The type of tooth receiving a post/core requirestwo considerations, aesthetics and direction offorces. A tooth in an aesthetically sensitive arearequiring an all-ceramic crown, needs a light-transmitting and tooth-coloured core. Secondly,the angle of the occlusal force is more relevantthan its magnitude.55 Anteriorly, the forcesencountered are inclined, explaining the greaterincidence of post-crown failures. Posteriorly, theocclusal forces are of greater magnitude but lessdamaging since they coincide with the long axisof the tooth, and are readily dissipated by theperiodontal ligament and alveolar bone. Due tothese heavier forces, cuspal coverage on posteriorteeth enhances long-term success. Finally, thetype of definitive restoration will also affect theamount of forces exerted, e.g. a single crown andFPD require different mechanical considerations.

Summary

Before embarking on post/core complexes, it isimperative to scrutinise the above factors, and ifthe clinical scenario is unsuitable, placing intra-radicular support is futile. Alternatives includeaccepting a poor prognosis, or extraction withsubsequent or immediate implant replacement.

NON-VITAL TEETH – CLINICAL PRACTICE

Having evaluated feasibility for intra-radicularanchorage, the following is a clinical protocol forpost placement and core build-up:

(1) Isolate tooth with rubber dam or non-impregnated gingival retraction cord (Hint5.5)

(2) If possible, carry out tooth preparation forthe final extra-coronal restoration to assessthe amount of remaining coronal dentinefor the ferrule effect

(3) If 1.5mm height of dentine is remaining,consider a direct technique, otherwise usean indirect method

Figure 5.38 Tooth preparation on right maxillary canine andlateral incisor to assess amount of remaining residual dentinebefore choosing an appropriate post/core.


(4) Select appropriate post system according to Table 5.3 and follow manufacturer’sinstructions for chosen post

(5) Shape post canal: either by an additive orsubtractive procedure:� Additive procedure (Figs. 5.39–5.44) –

if canal shape is oval, elliptical, flaredor with lateral iatrogenic channels orperforations, a flowable composite(with a DBA) is required to shape thecanal to the geometry of a prefabri-cated post, or creating a suitable pathof insertion/removal for an indirecttechnique ensuring that at least 4–5mmof root filling is present for a patentapical seal (Hint 5.6)

� Subtractive procedure – this involvesremoving radicular dentine to shapethe root canal for a post. This protocolassumes that the canal is of an accept-able shape for a preformed post. Thefirst step is removing the root fillingobturation material. The choice ofremoval methods depend on the rootfilling material. The removal methodsare chemical, thermal or mechanical.Chemical removal is useful for re-treating failed endodontic fillings, buthas limited scope for removing guttapercha (GP) since the amount ofremoval is difficult to assess. In addi-tion, some solvents, such as turpentine,cause dimensional changes in GP andincrease microleakage. The thermalapproach using heated instruments isideal for GP, but unsuitable for GI andresin-based root fillings. Mechanicalremoval, although the most destruc-tive, is the most widely used method for preparing root canals. Most postsystems are accompanied by twist drillscorresponding to post length and diam-eter. Initial shaping is performed withGates–Glidden burrs of progressivelyincreasing diameter, until the canalorifice corresponds to the twist drills of the chosen post system. Peeso drillsgenerate excessive heat that is harmfulto the periodontal cells and have a

propensity to melt rather than removeGP fillers56

(6) If an indirect technique is used, proceed tomake either a wax pattern or impression(Hint 5.7) and fabricate temporary postand crown (Hint 5.8). Forward to dentallab, and upon delivery follow from step 8below

(7) For a direct technique, post cementa-tion and core build-up is carried out concurrently

(8) If not already isolated, place rubber dam orretraction cord

(9) Choose core material (Table 5.1), andluting agent (Table 10.2, Chapter 10)

(10) Pre-treat post/core complex (Table 10.3,Chapter 10)

(11) Pre-treat post canal and coronal dentinewith a fifth generation DBA (Hint 5.9), mixluting agent and cement post

(12) Build up direct core on to post, followingmanufacturer’s instructions for the chosenmaterial

(13) Remove rubber dam (Hint 5.3)(14) Carry out immediate or delayed tooth

preparation (depending on the materialused) for the coronal restoration (Hint 5.4)

(15) Fabricate a chairside therapeutic temporaryrestoration to allow gingival healing, beforemaking an impression for the definitiverestoration (see Chapter 8).

Figure 5.39 Luimex post (Dentatus) case study: pre-operative radiograph showing inadequate root filling in maxillary second premolar.


Figure 5.40 Luimex post (Dentatus) case study: following re-root canal therapy, the coronal canal orifice is flared.

Figure 5.41 Luimex post (Dentatus) case study: flowablecomposite (with a dentine bonding agent) is placed in rootcanal and light cured with a light-transmitting post.

Figure 5.42 Luimex post (Dentatus) case study: the light-transmitting post is removed.

Figure 5.43 Luimex post (Dentatus) case study: a steel post,of identical diameter as the light-transmitting post, iscemented and trimmed.

Figure 5.44 Luimex post (Dentatus) case study: post-operative radiograph showing a new root filling, shaping theflared canal with flowable composite, and a steel post with acomposite core build-up.


� Hint 5.1 – If rubber dam placement is hin-dered by lack of tooth structure, a retrac-tion cord provides limited isolation forprotecting the periodontium, and creatingan arid environment

� Hint 5.2 – Retentive boxes and groovescan be created with either a 1mm cylin-drical diamond burr or 1mm tungstencarbide round burr. Care is necessary atthe proximity to the pulp chambers andfloors of cervical boxes in Class II cavities.For the latter, boxes or grooves should beat least 2–3mm within the outer margin ofthe proximal box to avoid perforation ofthe periodontal ligament

� Hint 5.3 – If retraction cord was utilisedinstead of a rubber dam, and tooth pre-paration is immediate, the cord can be left in situ during tooth preparation andfabrication of the therapeutic temporaryrestoration

� Hint 5.4 – If tooth preparation is carriedout immediately following fill-in or build-up, isolate the tooth and protect the softtissues with an appropriate sized retractioncord. The cord can be impregnated with

an astringent if crevicular bleeding isprevalent

� Hint 5.5 – A dry cord is ideal for absorb-ing crevicular fluids, visualising toothmargins and acting as an aegis for pro-tecting biologic width integrity. If haemor-rhage is anticipated, the cord can beimpregnated with an astringent, or alter-natively, a haemostatic agent can beapplied later on to the dry cord

� Hint 5.6 – The Luminex post system isideal for the additive procedure, whichuses a light-transmitting post for completepolymerisation of the flowable compositein the root canal

� Hint 5.7 – Use appropriate lubricant orseparating media to ensure post does notlock into the prepared root canal

� Hint 5.8 – Most indirect post systems haveplastic posts of corresponding sizes fortemporarisation

� Hint 5.9 – With chemically cured resinluting agents, avoid self-etching DBAs asthe acidic inhibition layer of the latter prevents complete polymerisation of theluting agent

Hints and Tips

References

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2 Huang, T.J., Schilder, H. and Nathanson, D.(1992) Effect of moisture content andendodontic treatment on some mechanicalproperties of human dentin. J Endod, 18,209–215

3 Manning, K.E., Yu, D.C., Yu, H.C. and Kwan, E.W. (1995) Factors to consider for predictable post and core build-ups of

endodontically treated teeth. Part II: Clinical application of basic theoretical concepts. J Canad Dent Assoc, 61(8),696–701

4 Fernandes, A.S. and Dessai, G.S. (2001)Factors affecting the fracture resistance ofpost-core reconstructed teeth: a review. Int JProsthodont, 14, 355–363

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8 Outwaite, W.C., Garman, T.A. and Pashley,D.H. (1979) Pin vs. slot retention in extensiveamalgam restorations. J Prosthet Dent, 41,396–400

9 Newsome, P.R.H. (1988) Slot retention: analternative to pins in the large amalgamrestoration. Dent Update, 15, 202–207

10 Baldwin, H. (1897) Cement and amalgam fill-ings. Br Dent Sci, XL, 193–234

11 Welbury, R.R. and Murry, J.J. (1990) Clinicaltrial of the glass-ionomer cement-compositeresin ‘sandwich’. Quintessence Int, 21,507–512

12 Prati, C. (1989) Early microleakage in Class IIresin composite restorations. Dent Mater, 5,392–398

13 Nash, R.W., Lowe, R.A. and Leinfelder, K.(2001) Using packable composites for directposterior placement. J Am Dent Assoc, 132,1099–1104

14 Demirel, F., Saygili, G. and Sahmali, S. (2005)Microleakage of endodontically treated teethrestored with prefabricated posts and tooth-colored restorative materials. Int J Periodon-tics Restorative Dent, 25(1), 72–79

15 Torbjorner, A. and Fransson, B. (2004) A lit-erature review on the prosthetic treatment ofstructurally compromised teeth. Int J Prostho-dont, 17, 369–376

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using quartz fibre, carbon-quartz fibre, andzirconium dioxide ceramic root canal posts. JAdhes Dent, 1, 153–158

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21 Marinez-Insua, A., Da Silva, L., Rilo, B. andSantana, U. (1998) Comparison of the frac-ture resistance of pulpless teeth restored witha cast post and core or carbon-fibre post witha composite core. J Prosthet Dent, 80,527–532

22 Hu, Y.-H., Pang, I.-C., Hsu, C.-C. and Lau,Y.-H. (2003) Fracture resistance of endodon-tically treated anterior teeth restored withpost-and-core systems. Quintessence Int, 34,349–353

23 Creugers, N.H., Mentink, A.G., Fokkinga,W.A. and Kreulen, C.M. (2005) 5-year follow-up of a prospective clinical study on varioustypes of core restorations. Int J Prosthodont,18(1), 34–39

24 Pontius, O. and Hutter, J.W. (2002) Survivalrate and fracture strength of incisors restoredwith different post and core systems andendodontically treated incisors without coro-noradicular reinforcement. J Endod, 28(10),710–715

25 Milot, P. and Stien, S. (1992) Root fracture inendodontically treated teeth related to postselection and crown design. J Prosthet Dent,68(3), 428–435

26 Quintas, A.F., Dinato, J.C. and Bottino, M.A.(2000) Aesthetic post and cores for metal freerestoration of endodontically treated teeth.Pract Periodont Aesthet Dent, 12(9), 875–884

27 Libman, W.J. and Nicholls, J.I. (1995) Loadfatigue of teeth restored with cast posts andcores and complete crowns. Int J Prosthodont,81, 155–161

28 Cooney, J.P., Caputo, A.A. and Trabert, K.C.(1986) Retention and stress distribution oftapered-end endodontic posts. J ProsthetDent, 55, 540–546

29 Burgess, J.O., Summitt, J.B. and Robbins,J.W. (1992) Resistance to tensile, compres-sion, and torsional forces provided by fourpost systems. J Prosthet Dent, 68, 899–903


30 Meyenberg, K.H., Luthy, H. and Scharer, P.(1995) Zirconia posts: a new all-ceramicconcept for nonvital abutment teeth. J EsthetDent, 7(2), 73–80

31 Butz, F., Lennon, A.M., Heydecke, G. andStrub, J.R. (2001) Survival rate and fracturestrength of endodontically treated maxillaryincisors with moderate defects restored withdifferent post-and-core systems: an in vitrostudy. Int J Prosthodont, 14, 58–64

32 Mitsui, F.H.O., Marchi, G.M., Pimenta,L.A.F. and Ferraresi, P.M. (2004) In vitrostudy of fracture resistance of bovine rootsusing different intra-radicular post systems.Quintessence Int, 35, 612–616

33 Buonocore, M.G. (1975) The nature of toothstructure in the use of adhesives in dentistry.Charles Thomas Publishers, Springfield

34 Javaheri, D. (2003) Techniques for nonvitalbleaching. Pract Proced Aesthet Dent, 15(6),483–485

35 Ahmad, I. (1998) Yttrium-partially-stabilisedzirconium dioxide (YPSZ): an approach torestoring coronally compromised non-vitalteeth. Int J Periodontics Restorative Dent,18(5), 455–465

36 Ahmad, I. (1999) Zirconium oxide post andcore system for the restoration of an endodon-tically treated incisor. Pract PeriodonticsAesthet Dent, 11(2), 197–204

37 Gluskin, A., Ahmad, I. and Herrero, D.B.(2002) The aesthetic post and core: unifyingradicular form and structure. Pract ProcedAesthet Dent, 14(4), 313–321

38 Paul, S.J., Pilska, P., Pietroban, N. andScharer, P. (1996) Light transmission of composite luting resins. Int J PeriodonticsRestorative Dent, 16, 165–173

39 Eckerbom, M., Magnusson, T. and Martins-son, T. (1991) Prevalence of apical periodon-titis, crowned teeth and teeth with posts in aSwedish population. Endod Dent Traumatol,7, 214–220

40 Lundgren, D. and Laurell, L. (1994) Biome-chanical aspects of fixed bridgework sup-ported by natural and endosseous implants.Periondontol 2000, 4, 23–40

41 Yang, H.S, Lang, L.A., Molina, A. and Felton,D.A. (2001) The effect of dowel design and

load direction on dowel-and-core restora-tions. J Prosthet Dent, 85, 558–567

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43 Maniatopoulos, C., Pillar, R.M. and Smith,D.C. (1988) Evaluation of strength at thecement-endontic post interface. J ProsthetDent, 59, 662–669

44 Sorenen, J.A. and Martinoff, J.T. (1984) Clinically significant factors in dowel design.J Prosthet Dent, 52, 28–35

45 Yoshida, T., Gomyo, S., Itoh, T., Shibata, T.and Sekine, I. (1997) An experimental studyof the removal of cemented double-retainedcast cores by ultrasonic vibration. J Endod,23, 239–241

46 Al-Ali, K., Talic, Y., Abduljabbar, T. andOmar, R. (2003) Influence of timing ofcoronal preparation on retention of cementedcast posts and cores. Int J Prosthodont, 16(3),290–294

47 Craig, R.G., Powers, J.M. and Wataha, J.C.(2002) Dental Materials. 11th edn. Mosby, StLouis

48 Akkayan, B. and Gulmer, T. (2002) Resistanceto fracture of endodontically treated teethrestored with different post systems. J Pros-thet Dent, 87, 431–437

49 Asmussen, E., Peutzfeld, A. and Heitmann, T.(1999) Stiffness, elastic limit and strength ofnewer types of endodontic posts. J Dent, 27,275–278

50 Freeman, M.A., Nicholls, J.I., Kydd, W.L. andHarrington, G.W. (1988) Leakage associatedwith load fatigue-induced preliminary failureof full crowns placed over three different postand core systems. J Endod, 24, 26–32

51 Akkayan, B. and Gomez, T. (2002) Resistanceto fracture of endodontically treated teethrestored with different post systems. J Pros-thet Dent, 87, 431–437

52 Junge, T., Nicholls, J.I., Phillips, K.M. andLibman, W.K. (1998) Load fatigue of com-promised teeth: a comparison of three lutingcements. Int J Prosthodont, 11, 558–564

53 Goodcare, C.J. and Spolnik, K.J. (1995) Theprosthodontic management of endodontically


treated teeth: a literature review. Part III.Tooth preparation considerations. J Prostho-dont, 4, 122–128

54 Caputo, A.A. and Standlee, J.P. (1987)Restoration of endodontically treated teeth.In: Biomechanics in Clinical Dentistry, pp.185–203. Quintessence, Chicago

55 Loney, R.W., Moulding, M.B. and Ritsco,

R.G. (1995) The effect of load angulation onfracture resistance of teeth restored with castpost and cores and crowns. Int J Prosthodont,8(3), 247–251

56 Ricketts, D.N.J., Tait, C.M.E. and Higgins,A.J. (2005) Tooth preparation for post-retained restorations. Br Dent J, 198,463–471

A laboratory-fabricated prosthesis, similar toother dental restorations, is essentially a fusionof two disparate materials to form a unifiedstructure. This combination of biological (tooth)and synthetic (restoration) components aims to repair or enhance a compromised dentition.Routinely, clinicians are faced with either treat-ing decay or improving aesthetics, both of whichinitially involve damaging remaining tooth sub-strate for achieving a therapeutic goal. Any sur-gical protocol inflicts trauma for the attainmentof a greater good, and tooth preparation is noexception. However, minimising surgical viola-tion mitigates iatrogenic insult, encourages fasterhealing and ensures longevity of the restoration.Unfortunately, scientific principles do not alwaysdictate tooth preparation, and instead are ration-alised by a variety of spurious factors. Theseinclude recommendations by peers, advertise-ments in journals, endorsement by opinionleaders or simply, a penchant for a particularproprietary product. Although this may appearsardonic, this is, nevertheless, not too far fromthe truth.


Reasons for extra-coronal restorations

The purpose of providing extra-coronal restora-tions are numerous; the reasons listed belowoften present concurrently for remedy:

� Resolving pathology, e.g. abscess, decay orfractures (Figs. 6.1 & 6.2)

� Improving function, e.g. decrease in OVD(Figs. 6.3–6.5)

� Enhancing aesthetics, e.g. misalignment,colour, shape, texture, erratic incisal plane,etc. (Figs. 6.6 & 6.7)

Before commencing tooth preparation, it isessential to reappraise the health, function, aes-thetic (HFA) triad discussed in Chapter 2.Having selected the most appropriate crown forthe prevailing clinical situation (Chapter 3), thenext step is to prepare the abutment tooth(teeth).

6Tooth preparation


Figure 6.1 Acute abscess associated with discoloured max-illary lateral incisor.

Figure 6.2 Post-operative view of patient in Figure 6.1showing resolution of periapical pathology following rootcanal therapy and an all-ceramic crown.

Figure 6.3 Pre-operative decrease in OVD.

Figure 6.4 Tooth preparations for new restorations at anincreased OVD.

Figure 6.5 Diagnostic wax-up for proposed increase inOVD.

Figure 6.6 Uneven, ‘rollercoaster’ incisal plane.

Tooth preparation 127

Biologic width

Chapter 2 emphasised the importance of pre-venting violation of the biologic width. The dis-cussion also pointed out that although presetaround every health tooth, the dimensions of thebiologic width vary, and differential diagnosis isessential. For restorative procedures, two land-marks are used, the free gingival margins (FGMs)or the alveolar bone crest (ABC). The choicedepends on clinical findings and judicious deci-sion-making. If the survival rate of a tooth is notto be undermined, maintenance of the biologicwidth is imperative. This includes invasion byretraction cord placement, preparation proce-dures (both rotary and hand instruments), crownmargin location and remnants of temporary or permanent cements. The manifestations ofviolating the biologic width depend on hostresponse, all of which ultimately compromiselongevity or survival of the tooth. Some exam-ples of biologic width violation include:

� Persistent inflammation (Fig. 6.8)� Asymmetrical gingival margins (Fig. 6.9)� Recession (Fig. 6.10)� Enlarged gingival embrasures (the so-called

‘black triangles’) (Fig. 6.11)� Periodontal pocketing (Fig. 6.12)

Figure 6.7 Restitution of incisal plane, coincident with cur-vature of mandibular lip. (Lab work by Willi Geller, Zurich,Switzerland.)

Figure 6.8 Persistent inflammation around crown on rightmaxillary central by crown margins impinging on the biologicwidth.

Figure 6.9 The anterior abutment (tooth #21) of a three-unitFPD shows recession (compared to the natural tooth 11) dueto biologic width violation at time of cementation, resultingin unsightly, asymmetrical gingival margins.

Figure 6.10 Gingival recession exposing margins of crownon left maxillary central.


Margin location

Crown margins can be supragingival, equigingi-val or subgingival (Fig. 6.13). From the afore-mentioned discussion, it becomes apparent thatsupra- and equigingival margin placement is in-consequential to the biologic width. Supragingi-val margins are indicated where aesthetics are oflittle concern, e.g. for posterior restorations, oranteriorly when the patient presents with a lowlip line (Fig. 6.14). Equigingival margins arereserved for all-ceramic restorations, such asPLVs, with the proviso that the underlying toothsubstrate is of an acceptable colour, avoiding anobvious cement line and colour change betweenthe restoration and tooth (Fig. 6.15).

Figure 6.11 Enlarged gingival embrasures (black triangles)between crowns on maxillary incisors.

Figure 6.12 Pocket formation and periodontal abscess asso-ciated with defective crown on right maxillary lateral incisor.

CEJ

SupragingivalEquigingivalSubgingival

Figure 6.13 Crown margins can be supra-, equi- or subgingival.

Figure 6.14 Patient with a low lip line concealing the cer-vical margins of the maxillary dentition.

Figure 6.15 Porcelain laminate veneer preparations for themandibular central incisors with equigingival margins (noticethat the underlying tooth is of an acceptable colour).


However, subgingival margins are of para-mount clinical significance. As a generalisation,if the ABC is used as a landmark for the biologicwidth, and sulcus depth permitting, intra-crevic-ular margin location should be placed at approx-imately half the width of the prevailing crevice.The rationale for this is that like politics, toothpreparation is an art of the possible, rarely ofperfection. Hence, aiming to place a margin halfthe depth of the sulcus gives a degree of latitudeso that, should the preparation inadvertentlydeviate from the ideal, the additional depth stillprevents impingement into the epithelial attach-ment part of the biologic width. Additionally,placing margins half way in the crevice leavessufficient space for gingival cord placement; thisacts as an aegis between the epithelial attachmentand the bur as well as compensating for post-preparation gingival recession, ensuring that themargins are still subgingival. On the other hand,if the FGM is used as a reference point for thebiologic width, intra-crevicular margins shouldbe placed 0.5mm within the sulcus. Subgingivalplacement becomes a necessity for critical aes-thetic sites, e.g. patients with a high lip line orexcess gingival exposure during a relaxed smile(Figs. 6.16–6.18).

Tooth preparation should follow the circum-ferential FGM, which mimics the underlyingalveolar bone architecture and hence ensures biologic width integrity (Fig. 6.19). Care is

Figure 6.16 Patient with a high lip line, exposing excess gin-givae during a relaxed smile, requires crowns with subgingi-val margin location.

Figure 6.17 Closer view of patient in Figure 6.16 showingsupragingival defective crown margins of crowns on maxil-lary centrals.

Figure 6.18 Temporary crowns with subgingival crownmargins for patient in Figure 6.17.

Figure 6.19 Crown preparation margins should follow thegingival margin and hence the underlying alveolar bonearchitecture.


necessary to avoid a pitfall in the interproxi-mal region where sulcular depth is generous(>2.5mm). Margins could be placed deeper thanthe mid-facial level, but this results in ‘black tri-angles’ due to interproximal recession leading toa compromise in ‘pink aesthetics’. Therefore, itis wiser to prepare a tooth mimicking the gingi-val scallop around its circumference, at a fixedpredetermined level (Fig. 6.20).

Margin geometry

A variety of margin designs are proposed for all-ceramic and bonded crowns. Opinions aredivided depending on the factor taking pre-cedence, i.e. aesthetic, mechanical properties ofmaterial, ease of fabrication and tooth prepara-tion considerations.

The most popular designs include the featheror knife-edge, shoulder and chamfer. Marginalintegrity, in terms of opening at the tooth/crowninterface, has varying clinical acceptance withreports citing discrepancies of 120µm, 100µmand 50µm.1,2,3 The featheredge design, with anopening of 135µm fails even the most lax accept-ability of 120µm, making its application ques-tionable.4 This margin design is indicated forall-metal crowns, which require minimal toothpreparation (Fig. 6.21). Furthermore, a knife-

edge finish line is difficult to discern on a plasterdie and can lead to poor marginal adaptability,the lack of tooth reduction results in both ver-tical and horizontal over-contouring of therestoration, leading to changes in the bacterialflora, with ensuing chronic inflammation andattachment loss of the surrounding periodontalligament.5 If knife-edge margins are used, theyshould be burnished and located supragingivallyto avoid over-contouring or an incorrect emer-gence profile.

The shoulder preparation also shows diversityin geometry, with axiogingival angles rangingfrom 90–120° (Fig. 6.22). In a study using finite

Figure 6.20 Clearly discernible crown margins mimickingthe gingival scallop on maxillary left central.

Figure 6.21 Feather or knife-edge finish line.

Figure 6.22 Shoulder finish line.


element analysis to ascertain total strain ofporcelain stresses on shoulders of 90°, 120° andchamfer preparations, the chamfer showed mostresilience.6 While limited in its conclusions, thisstudy questions conventional teaching of usingshoulders when porcelain contacts the preparedtooth margin. A shoulder may be acceptable if ametal–ceramic crown is being replaced with anall-ceramic unit, and creating a chamfer wouldnecessitate further tooth removal. Other benefitsof a chamfer finish line include a marginalopening of 68µm, facilitating scanning devicesfor CAD/CAM copings, expediting crown prepa-ration,7 and preserving more natural tooth incomparison to a 90° shoulder. Furthermore, achamfer is aesthetically better than a shouldersince there is a gradual colour transition betweenthe restoration and tooth substrate, avoiding anabrupt delineation between tooth and crown(Fig. 6.23).8

Finally, removal of serrated overhangingenamel prisms or the ‘enamel lip’ is needed to obtain a distinct and visible finish line. Ar-mamentarium employed for this task includesenamel trimmers (hand instruments), rotary andreciprocating diamond tips. The smoothest finishline is obtained using diamond tips, of progres-sively finer grits, in a reciprocating handpiece(Fig. 6.24).9

Preparation design

The retention, resistance and convergence taperharmony influence tooth preparation design.Retention is resistance to displacement along thepath of insertion of a restoration; i.e. the forceneeded to ‘pull out’ the prosthesis. As a generalguide, at least 3mm of natural tooth abutment isnecessary for adequate retention and resistance,irrespective of the luting agent. Whilst retentionhas been demonstrated to have a linear relation-ship to preparation diameter and height, it is lessrepresentative of forces generated in the oralenvironment compared to resistance.10,11 Masti-catory and parafunctional force vectors encoun-tered are lateral in nature, ranging frombuccolingual, occlucogingival and linguobuccal.These non-axial forces cause fatigue, defined as cyclic loading over time. Counterbalancingfatigue, and hence improving the long-termsuccess of a prosthesis, is dependent on the resist-ance, as opposed to retention form, of the pre-pared abutment. Resistance also demonstrates alinear relationship to height or diameter of thepreparation. Additionally, resistance to fractureis also dependent on choice of cement, e.g. composite resin has three times the resistance to fracture compared with zinc phosphate.12

Figure 6.23 Chamfer finish line. Figure 6.24 ‘Enamel lip’ following tooth preparation (rightside) is removed with diamond tips in a reciprocating hand-piece (left side).


Furthermore, using DBAs helps transfer occlusaland masticatory loads to the underlying toothsubstrate for dissipation by the periodontal ligament.13

A 6° taper on each proximal wall, making atotal convergence angle of 12°, is regarded as thestandard norm (Figs. 6.25–6.27).14 The totalocclusal convergence of the preparation shows alinear, as opposed to hyperbolic, relationship toresistance to dynamic lateral loading.15 Thereforevarying the convergence angle by ±10° willincrease or decrease resistance by 5–10%. Addi-tionally, taper has a bearing on the compressivestrength of the cement layer. A gradual taperexaggeration will progressively cause the cementarea under compression to tend towards zero.16

It is important to realise that the cement com-pression is progressive, and does not exhibit agiven cut-off point or ‘limiting taper’ dependingon the convergence angle.17 Therefore, althougha taper increase will decrease resistance, there isno finite total convergence angle below whichcement failure is inevitable.

The proverbial 1.5mm reduction for metal–ceramic crowns is based on 0.5mm for the metalsubstructure, and 1mm for the veneering porce-lain; this is purely to obtain depth of colour forachieving the desired aesthetics. Structurally, a thinner labial porcelain shoulder (less than 1mm) is better suited to withstand tensilestresses for both labially and palatally angledloads. Other studies have further concluded thata thicker porcelain layer does not improve frac-ture resistance or longevity of crowns.18 In fact, the uniformity of tooth reduction, ensuring auniform porcelain layer, is more significant thanthe actual thickness of the porcelain layer.

Many clinicians assume that all-ceramic toothpreparation is more conservative than that formetal–ceramic units. This may be true for uni-layer feldspathic crowns, but is untrue for mostcontemporary bi-layer ceramic prostheses. Inorder to accommodate both the dense ceramiccore and veneering porcelain, tooth reduction isusually 1.3–1.6mm, almost identical to metal–ceramic crowns. For example, if a Procera copingof 0.6mm is required, tooth reduction is carriedout with a 1.6mm diameter bur, producing a

Figure 6.25 Ideal tooth preparations: 12° convergenceangle.

Figure 6.26 Ideal tooth preparations: plaster cast showingcorrectly trimmed dies with definitive crowns-to-preparationrelationship.

Figure 6.27 Ideal tooth preparations: definitive Proceraalumina crown for patient in Figures 6.25 and 6.26.


reduction of 0.6mm for the alumina coping and1mm for the veneering porcelain.

Tooth reduction for PLVs is usually confinedto the facial aspect, and dictated by the purposeof the intended treatment (Fig. 6.28). If PLVs are used to mask discolouration, the reductiondepends on the extent of discolouration and thedesired final shade. However, if PLVs are used to‘re-align’ teeth, the reduction depends on thelocation of the tooth within the arch. Palatallyinclined teeth requiring buccal alignment willneed minimal preparation, and buccally placedteeth requiring palatal alignment will necessitateextensive tooth reduction.

Maintenance of dental hard tissue integrity

Tooth preparation, particularly for cosmeticreasons, is essentially an assault on healthy tissueto achieve a desired result. Whilst in the major-ity of cases the means justify the ends, precau-tions are necessary to mitigate damage to thetriune tooth (enamel, dentine and pulp). Amountof tooth reduction is dictated by parameters suchas aesthetics, obtaining a minimum thickness toavoid compromising strength of the restorativematerial, occlusion and pulp chamber size.

Various studies have reported non-vitality ofteeth restored with artificial crowns.19,20,21 Causes

for non-vitality can be due to a dentine wound,dehydration of dentine and temperature eleva-tion during preparation stages. Thermal shock tothe pulp is dependent on pulpal dimensions andsize, amount of calcified dentine and preparationtechniques. The first two factors are uncontrol-lable but should be visualised radiographicallybefore preparation is initiated. The last factor isprimarily operator determined.

While using coarser diamond grit sized burs is procedurally expedient, it does, however,produce elevated temperatures within the pulpchamber. For example, using a 150µm diamondgrit bur raises the temperature to 40.5°C (equiv-alent to a temperature increase of 3.2°C), pre-cariously close to the critical limit of 41.5°C forpulpal necrosis. On the other hand, a fine 30µm diamond grit bur causes an intra-pulpaltemperature increase of only 2.5°C. Other con-tributors to temperature increase are increasedgrinding time, relentless grinding, increased burpressure, lack of hydraulic cooling and a coolingwater temperature in excess of 32°C. Finally, asthe dentine layer decreases with progressivestages of tooth preparation, its heat absorptioncapacity also diminishes. Therefore, in the finalstages of preparation it is prudent to use burs offiner grits, as this causes less temperature eleva-tion than coarser grits (Fig. 6.29).22

It should also be noted that the pulp has a ‘memory’ and remembers successive assaults for restorative procedures. Excluding cosmetic

Figure 6.28 PLV tooth preparations on right maxillarycanine and lateral incisor.

Figure 6.29 Using burs of progressively finer diamond grit(and tungsten-carbide finishing burrs) minimises pulpal tem-perature elevation.


reasons, a crown is probably the penultimaterestoration, where previous fillings have failed,prior to extraction and implant placement. Con-sidering these factors, the cumulative effect ofrepeated restorations eventually yields to pulpalnecrosis. As a result, it is crucial to limit the timefor tooth preparation to an absolute minimum,preventing damage to an already compromisedpulp. Using as few burs as possible, minimalcontact time with the tooth, copious irrigationand pausing to allow thermal dissipationachieves this objective.

For all-ceramic crowns, such as Procera(Nobel Biocare, Sweden), preparation is expe-dited by using only two types of burs. TwoProcera bur kits are available, the coarse kit thatcontains burs of a 125µm diamond grit, and themedium kit that has burs with a 100µm grit,both below the critical 150µm grit. Each kit con-tains burs of only two shapes (Fig. 6.30). Thefirst is a chamfer of varying widths (1.4mm, 1.6mm and 1.8mm) for circumferential reduc-tion and an oval or elliptical shape for occlusalor palatal clearance of 1.5 to 2mm. Using onlytwo burs firstly simplifies preparation andensures a calculated predetermined amount oftooth removal. Another advantage of the latteris that the diameter of chamfer bur also corre-sponds to the Procera copings. For example, for

anterior tooth, using a 1.4mm bur will corre-spond to a 0.4mm Procera coping, leaving 1mmfor the veneering porcelain (Fig. 6.31) and, forposterior teeth, a 1.6mm bur will accommodatea 0.6mm coping with 1mm veneering porcelain(Fig. 6.32).

Another reason for sparingly using coarserdiamonds is minimising enamel cracks at thepreparation margins, resulting in reduced enameltoughness due to crack propagation within theenamel. To ‘seal’ any cracks, using diamonds ofprogressively finer grits removes median-typeand micro-cracks between and within enamelrods. Adopting this protocol ensures the result-

Figure 6.30 The Procera tooth preparation kits are availablein medium and coarse, with diamond grit sizes of 100µm and150µm, respectively. Both kits contain burs of only twoshapes, the chamfers and elliptical configurations, expeditingtooth preparation.

Figure 6.31 Incisors and canines are prepared with a 1.4mm chamfer and an elliptical bur for palatal reduction.

Figure 6.32 Premolars are prepared with a 1.6mm chamferand an elliptical bur for occlusal reduction.


ant preparation margins are stronger with fewercracks.23

The final surface roughness of the preparationhas also been a topic of debate in the dental lit-erature. While some studies have shown littlevariance in retentive forces between rough andsmooth preparations,24,25,26 others have showngreater retention when a tooth surface is pre-pared with coarser diamond burs.27,28 Rough-ness, measured in terms of Ra, of a 120µmdiamond bur is 6.8Ra, while that for a tungstencarbide finishing bur is 1.2Ra (Fig. 6.33). Dis-advantages of a rougher surface are potentialmicro undercuts causing failure in completeseating of a restoration, inaccurate castings if alost wax technique is employed and trapping airwithin the cement layer. Conversely, excessivelysmooth surfaces may cause restoration dislodge-ment with traditional, non-adhesive cements.Although not conclusive, but considering theabove points, and the discussion relating to in-creased temperature and enamel subsurfacedamage with coarser grits, it is probably prudentto veer towards a smoother preparation surfacefinish.

Tooth preparation, not unlike soft tissue sur-gical procedure, necessitates wound closure. This includes debridement (etching with phos-phoric acid to remove smear layer), disinfectionand sealing to prevent bacterial invasion (appli-cation of DBA for hybridisation) and dressing

with bandage (therapeutic temporary crown) to expedite healing. This protocol also reducespost-operative sensitivity, a frequent occurrencefollowing tooth preparation, as well as im-proving the bond strength of the definitiverestoration.29,30

Cutting efficiency

The cutting efficiency (CE) is dependent on amyriad of factors, including type of biological orrestorative material to be cut (enamel, dentine,ceramic, cast metal or resin composite, etc.),operator kinaesthetic sense, handpiece speed and rugosity and quality of the rotary instru-ment. The belief that coarser grit diamond burs(>150µm) are more efficacious is fallacious. Arecent study reports that there is no increase inCE using coarser grits compared to usingmedium grits (100µm).31 The force applied onthe handpiece during preparation is anotherpoint of contention. Using light pressures tendsto smooth a surface, while excessive force causespulpal damage. Furthermore, increasing thehandpiece load is self-limiting, little improve-ment in CE is observed beyond the clinical normrange of loads between 50g and 150g.32 Whatseems pertinent is degradation and debris accu-mulation of a bur, contributing to a decrease incutting efficiency.33 Using an ultrasonic bath toremove debris, prior to sterilisation, is thereforeinvaluable.

Table 6.1 summarises the salient points regard-ing tooth preparation.

CLINICAL PRACTICE

Anterior tooth preparation

To demonstrate the theoretical aspects, the fol-lowing case study shows a sequence for toothpreparation for anterior all-ceramic crownsusing the Assessment Planning Treatment (APT)acronym.

Figure 6.33 Completing preparations with a tungstencarbide finishing bur produces a smoother surface finish withenhanced enamel margin integrity.


Assessment

(1) Blatant diastemae in maxillary and man-dibular arches (Fig. 6.34)

(2) Maxillary median diastema of 5mm(3) Distal flaring of central incisors(4) Palatal erosion due to previous episode of

bulimia (Fig. 6.35)(5) Anterior class I relationship(6) Financial constraints limited treatment to

maxillary arch. Furthermore, the mandibu-lar lip concealed the lower anterior teethduring a relaxed smile

Planning

(1) Initial fixed orthodontic appliances to reducediastemae and parallel roots to mitigate dis-tal flaring of maxillary incisors

(2) Create a favourable width/length ratio ofincisors

(3) Ensure wide contact points between incisorsto prevent orthodontic relapse

(4) Provision of four full coverage Procera(alumina) crowns, for high strength andenhanced aesthetics

Table 6.1 Synopsis of factors determining tooth preparation.

Factor Protocol

Crown margin placement Depends on ABC or FGM landmark and sulcus depth: ideally placed at half prevailing sulcus depth

Margin geometry Chamfer (unless metal–ceramic crown is being replaced with an all-ceramic unit)

Preparation design (1) 12° total convergence angle(2) Maximise preparation height and diameter(3) Minimise tooth reduction depending on type of final crown(4) Use composite resin as luting cement(5) Mean reductions: metal–ceramic = 1.5mm, ceramic = 1.3–1.6mm

(depending on all-ceramic system)

Dental tissue integrity (1) Determine size and location of pulp radiographically(2) Determine degree of dentine calcification(3) Avoid using ultra-coarse burs (>150µm)(4) Use a water cooling temperature below 32°C(5) Prepare tooth in intervals to allow heat dissipation(6) Ensure a smooth surface roughness(7) Seal with DBAs immediately after preparation

Cutting efficiency (1) Use diamond burs of medium grit (<150µm)(2) Avoid excessive handpiece pressure(3) Discard degraded or damaged burs(4) Clean soiled burs in ultrasonic bath

Figure 6.34 Pre-operative view showing diastemae in botharches and poor oral hygiene.


Treatment

(1) Initial scaling and polishing with prophy-lactic and orthodontic therapy (Figs. 6.34–6.38)

(2) Decide on crown margin location position(in this case equigingival due to minimumsulcus depth). If margins are to be subgin-gival, use either ABC or FGM for ensuringbiologic width integrity. Using ABC as alandmark, measure entire dentogingivalcomplex from free gingival margins to alveolar crest under local anaesthesia atfour sites around tooth (mesial, distal,buccal/facial and lingual/palatal), deduct 2mm (for biologic width) to determinesulcus depth. Also, confirm location of CEJfor differential diagnosis of erratic ABC.Alternately if FGM is used as a landmark,place margins 0.5mm within sulcus (Figs.6.39 & 6.40)

(3) Place retraction cord, of appropriate width,within gingival sulcus to protect epithelialattachment (Figs. 6.41 & 6.42) (Hint 6.1)

(4) Use 1.4mm chamfer burs (0.4mm copingand 1mm veneering porcelain), place depthcuts mesio-distally following crown con-tour curvature (Fig. 6.43)

(5) Repeat step (4) above for inciso-gingivaland palatal aspects (in this case no palatalreduction was necessary) (Fig. 6.44)

(6) Reduce tooth according to initial depth cutson all aspects (elliptical diamond for palatalreduction and occlusal clearance of 1.5–2mm) (Fig. 6.45)

(7) Refine surface roughness with a 1.4mm 12-fluted tungsten-carbide chamfer and ellipti-cal burs (Fig. 6.46)

(8) Complete tooth preparation by removingcircumferential enamel lip with diamondtip in a reciprocating handpiece

(9) Verify sinuous outline and smooth surfacefinish of tooth preparations

(10) Etch, blot dry and seal preparations withDBAs. Light through a glycerine gel coverto avoid interaction of oxygen inhibitionlayer with acrylic monomers (used for ther-apeutic temporary crowns) and impressionmaterials34

(11) Proceed with therapeutic temporary crownfabrication

(12) At a subsequent visit, verify gingival healthand stability of FGM before makingimpressions (Figs. 6.47–6.49)

(13) Check plaster model for clearly discerniblecircumferential tooth margins, and sinuouspreparation outlines (Fig. 6.50)

(14) Preparations-to-definitive crowns relation-ship is shown in Figure 6.51.

Figure 6.35 Initial maxillary median diastema of 5mm,distal flaring and palatal erosion of the central incisors.

Figure 6.36 Facial view of fixed orthodontic appliance insitu to reposition maxillary anterior sextant.


Figure 6.37 Palatal view of fixed orthodontic appliance insitu to reposition maxillary anterior sextant.

Figure 6.38 Orthodontic appliance removal, prophylaxis toimprove periodontal health and reduction of mediandiastema to 2mm.

Figure 6.39 Mid-facial dentogingival complex measurementwith a periodontal probe. The linear measurement is 2.0mmindicative of a negligible sulcus depth.

Figure 6.40 Distal dentogingival complex measurementwith a periodontal probe. The linear measurement is 4.5mmwith a sulcus depth of 2.5mm.

Figure 6.41 Retraction cord around tooth #11 to protect gin-gival margins.

Figure 6.42 Zekrya gingival retractor to protect the FGMduring crown preparation.


Figure 6.43 Mesio-distal depth grooves for precise toothreduction.

Figure 6.44 Mesio-distal and inciso-gingival depth groovesfor precise tooth reduction.

Figure 6.45 Precise tooth reduction using the depth cuts asa guide in both mesio-distal and inciso-gingival planes.

Figure 6.46 Tungsten carbide bur being used to create asmooth surface finish.

Figure 6.47 Completed tooth preparations showing distinctchamfer margins on maxillary incisors.

Figure 6.48 Right lateral view showing favourable tissueresponse following tooth preparations with sharp interdentalpapillae and gingival stippling.


Posterior tooth preparation

The following case study shows a tooth prepa-ration sequence for an all-ceramic crown usingthe ATP acronym.

Assessment

(1) Heavily restored mandibular right firstmolar (tooth #46) (Fig. 6.52)

(2) Defective amalgam, leaky margins(3) Sensitivity to temperature and sugary foods

(vital tooth)(4) No parafunctional habits (bruxism, etc.)(5) No eccentric lateral or protrusive occlusal

contacts.

Planning

Treatment options include:� Replacing the amalgam – but due to decay

and minimal remaining tooth structure, adirect filling would require pin retention,further weakening an already compromisedtooth

� A ceramic inlay is also contra-indicated dueto extensive tooth loss

� Extra-coronal restoration, e.g. metal–ceramic crown. Patient declined use of intra-oral metal

� Procera (alumina) full coverage crown forhigh strength (using 0.6mm coping) andsuperior aesthetics.

Figure 6.49 Left lateral view showing favourable tissue reac-tion following tooth preparations with sharp interdental papil-lae and gingival stippling.

Figure 6.50 Plaster cast showing smooth preparations withsinuous outlines, devoid of undercuts.

Figure 6.51 Plaster cast showing definitive crown-to-toothpreparation relationship.


Treatment

(1) Remove amalgam under rubber dam isolation

(2) Build-up tooth with resin composite fillingmaterial using DBAs and intra-coronal slotsand grooves for additional retention

(3) Determine sulcus depth and place retrac-tion cord of appropriate width

(4) Use 1.6mm chamfer bur to place depth onall aspects (Fig. 6.53)

(5) Complete tooth reduction ensuring asmooth outline, devoid of undercuts (Fig.6.54)

(6) Protect with DBA as for anterior crowns(7) Fabricate therapeutic temporary crown(8) At a subsequent visit, verify gingival health

before making impressions (Fig. 6.55)(9) In the dental laboratory, using CAD/CAM

Procera technology, scan die for a 0.6mmcoping

(10) Veneer coping with low fusing veneeringporcelain (Fig. 6.56)

(11) At try-in bisque bake stage, check andadjust occlusal contacts (blue = workingcontacts, green = non-working) (Fig. 6.57)

(12) Return crown to dental laboratory for pol-ishing and glazing

(13) Cement definitive crown (Fig. 6.58)

Figure 6.52 Pre-operative defective failing amalgam restora-tion in mandibular molar.

Figure 6.53 Circumferential and occlusal depth cuts incomposite core build-up.

Figure 6.54 Completed tooth preparation with retractioncord in situ.

Figure 6.55 Gingival health apparent one week followingtooth preparation, ready for impression making.


The final crown restores health, function andaesthetics. Furthermore, opposing tooth wear isminimised due to the low abrasive veneeringporcelain.

Figure 6.56 Plaster cast showing definitive crown-to-toothpreparation relationship.

Figure 6.57 Adjusting occlusion at the bisque try-in stage.

Figure 6.58 Cemented Procera alumina crown restoringhealth, function and aesthetics.

Hints

� Hint.6.1 – If additional gingival protec-tion and retraction are necessary, use theZekrya gingival retractor (Dentsply) (seeFig. 6.42)

References

1 McLean, J.M. and von Frauhofer, J.A. (1971)The estimation of cement film thickness by anin vivo technique. Br Dent J, 131, 107–111

2 May, K., Russel, M., Razzoog, M. and Lang,B. (1996) Precision of fit of the Procera All-Ceram crown. University of Michigan, JPD,No.4

3 West, A.J., Goodacre, C.J., Moore, B.K. andDykema, R.W. (1985) A comparison of fourtechniques for fabricating collarless metal-ceramic crowns. J Prosthet Dent, 54, 636–642

4 Lin, M.T., Sy-Munoz, J., Munoz, C.A.,Goodacre, C.J. and Naylor, W.P. (1998) Theeffect of tooth preparation form on the fit of Procera copings. Int J Prosthodont, 11,580–590

5 Lang, N.P., Kiel, R.A. and Anderhalen, K.(1983) Clinical and microbiological effects ofsubgingival restorations with overhanging orclinically perfect margins. J Clin Periodontol,10, 563–578

6 Seymour, K.G., Taylor, M., Samarawickrama,D.Y.D. and Lynch, E. (1997) Variation inlabial shoulder geometry of metal ceramiccrown preparation: a finite element analysis.Eur J Prosthodont Rest Dent, 5(3), 131–136

7 Bishop, K., Biggs, P. and Kelleher, M. (1996)Margin design for porcelain fused to metalrestorations which extend onto root. Br DentJ, 180, 177–184


8 Burke, F.J.T. (1996) Fracture resistance ofteeth restored with dentine-bonded crowns:the effect of increased tooth preparation.Quintessence Int, 27(2), 115–121

9 Kippax, A.J., Shore, R.C. and Basker, R.M.(1996) Preparation of guide planes using areciprocating handpiece. Br Dent J, 180(6),216–220

10 Kaufman, E.G., Coehlo, D.H. and Colin, L.(1961) Factors influencing the retention ofcemented gold castings. J Prosthet Dent, 11,487–502

11 Maxwell, A.W., Blank, L.W. and Pelleu, G.B.(1990) Effect of crown preparation height onthe retention and resistance of gold castings.Gen Dent, 200–202

12 Wiskott, H.W.A., Nicholls, J.I. and Belser,U.C. (1997) The effect of tooth preparationheight and diameter on the resistance of com-plete crowns to fatigue loading. Int J Prostho-dont, 10(3), 207–215

13 Jensen, M.E., Sheth, J.J. and Tolliver, D.(1989) Etched-porcelain resin-bonded full-veneer crowns: in vitro fracture resistance.Compend Contin Educ Dent, 10, 336–347

14 Burke, F.J.T. and Watts, D.C. (1994) Fractureresistance of teeth restored with dentine-bonded crowns. Quintessence Int, 25, 335–330

15 Jorgensen, K.D. (1995) The relationship be-tween retention and convergence angle incemented veneer crowns. Acta OdontolScand, 13, 35–40

16 Hegdahl, T. and Silness, J. (1997) Preparationareas resisting displacement of artificialcrowns. J Oral Rehabil, 4, 201–207

17 Parker, M.H., Gunderson, R.B., Gardner, F.M.and Calverley, M.J. (1988) Quantitative deter-mination of taper adequate to provide resist-ance form: concept of limiting taper. JProsthet Dent, 59, 281–288

18 Malament, K.A. and Socransky, S.S. (1999)Survival of Dicor glass-ceramic dental restora-tions over 14 years. Part II: effect of thicknessof Dicor material and design of tooth prepa-ration. J Prosthet Dent, 81, 662–667

19 Bergenholtz, G. and Nyman, S. (1984) Endon-tic complications following periodontal andprosthetic treatment of patients with ad-

vanced periodontal disease. J Periodontol, 55,63–68

20 Spiering, T.A., Peters, M.C. and Plasschaert,A.J. (1985) Thermal trauma to teeth. EndodDent Truamatol, 1, 123–129

21 (1995) Fixed prosthodontics, avoiding pulpdeath. Clin Res Assoc Newsletter, 19(1), 1

22 Ottal, P. and Lauer, H.-C. (1998) Temperatureresponse in the pulpal chamber during ultra-high-speed tooth preparation with diamondburs of different grit. J Prosthet Dent, 80,12–19

23 Xu, H.H.K., Kelly, J.R., Jahanmir, S., Thompson, V.P. and Rekow, E.D. (1997)Enamel subsurface damage due to toothpreparation with diamonds. J Dent Res,76(10), 1698–1706

24 Smith, B.G. (1970) The effect of the surfaceroughness of prepared dentine on the reten-tion of castings. J Prosthet Dent, 23, 187–197

25 Ayad, M.F., Rosenstiel, S.F. and Salama, M.(1997) Influence of tooth surface roughnessand type of cement on retention of completecast crowns. J Prosthet Dent, 77, 116–121

26 Darveniza, M., Basford, K.E., Meek, J. andStevens, L. (1987) The effect of surface rough-ness and surface area on the retention ofcrowns luted with zinc phosphate cement.Aust Dent J, 32, 446–457

27 Smyd, E.S. (1952) Dental engineering appliedto inlay and fixed bridge fabrication. J Pros-thet Dent, 2, 536–542

28 Tuntiprawon, M. (1999) Effect of tooth sur-face roughness on marginal seating and reten-tion of complete metal crowns. J ProsthetDent, 81, 142–147

29 Bertschinger, C., Paul, S.C., Luthy, H. andScharer, P. (1996) Dual application of dentinebonding agents: effect on bond strength. AmJ Dent, 9, 115–119

30 Paul, S.J. and Scharer, P. (1997) The dualbonding technique: a modified method toimprove adhesive luting procedure. Int J Peri-odontics Restorative Dent, 17, 536–545

31 Siegel, S.C. and von Fraunhofer, J.A. (1996)Assessing the cutting efficiency of dental burs.J Am Dent Assoc, 127, 763–772


32 Eames, W.B. and Nale N.L. (1973) A com-parison of cutting efficiency of air-drivenfissure burs. J Am Dent Assoc, 86, 412–415

33 Siegel, S.C. and von Fraunhofer, J.A. (1999)Dental cutting with diamond burs: heavy-handed or light touch. J Prosthod, 8, 3–9

34 Magne, P. and Belser, U. (2002) Immediatedentin bonding. In: Bonded PorcelainRestorations in the Anterior Dentition – ABiomimetric Approach. pp. 270–273. Quin-tessence, Berlin

Introduction

Many synonyms are used to describe temporaryrestorations, including provisional, interim, pro-totype, non-permanent, transitional, pro-temp,short-term or disposable. The terminology issubjective, but the salient point is that a tempo-rary restoration is not perceived as a stopgap,awaiting delivery of the final restoration or pros-thesis. On the contrary, a temporary should beutilised to foresee, and correct potential prob-lems so that aberrations are not incorporatedinto, or jeopardise, the permanent restoration.Consequently, a temporary, besides longevityand colour, is essentially identical to its definitivecounterpart. Furthermore, an appropriate des-cription of this restoration is therapeutic, sinceat this stage all pathology is resolved for attain-ing health and a stable environment prior tofitting the permanent unit(s). This implies achiev-ing health and stability of both hard and softtissues before, not after fitting the definitiverestoration.


As discussed in Chapter 2, the requisite of a dental restoration is sequentially achievinghealth, function and aesthetics (HFA triad), andthe therapeutic temporary restoration (TTR) isno exception. By definition, the first requirementof a TTR is retrievability, for access to the under-lying prepared abutment and surrounding hardor soft tissues, for carrying out further treatment.The discussion below starts with the HFA triad,and then highlights requirements of a TTR.

Health

The primary objective of any therapy is estab-lishing and maintaining health. In the case of atemporary restoration, its remedial role is notlimited to the health of the prepared tooth sub-strate, but also to the surrounding periodontal

7Therapeutic temporary restorations


tissues and adjacent and opposing dentition. Forvital teeth, pulpal protection is essential, whilefor endodontically treated teeth, a coronal seal iscrucial for preventing microleakage and subse-quent ingress of microorganisms into the rootcanal and periapical regions. A hermetic seal ofthe temporary crown with the abutment is there-fore essential.

The first item to scrutinise is tooth pre-paration, including retention, resistance, sinuousoutline, absence of undercuts, parallelism, con-vergence angle and surface roughness (Fig. 7.1).Next, endodontic evaluation is carried out,which may necessitate initial or re-root canaltherapy to rectify a defective root canal filling,apicectomy, intra-radicular support and subse-quent core build-up, or extracting a tooth with poor prognosis with subsequent implantreplacement.

Marginal integrity is also essential for achiev-ing periodontal health; this is dependent on acorrect emergence profile and appropriate crownmorphology conducive for oral hygiene proce-dures. Modifications are carried out, and oralhygiene reinforced until inflammation is resolvedresulting in a coral colour appearance of theperiodontium with knife-edge free gingivalmargins and stippling of the attached gingiva(Fig. 7.2). Stability of the gingival architecture is essential before impressions are attempted. If gingival hypertrophy is evident, soft tissue

resection and/or alterations to the temporariesare indicated. Alternatively, gingival recessionrequires modifications of the tooth preparationfor subgingival margin concealment. This is espe-cially relevant when crown lengthening or tissuegrafts are performed concurrently with toothpreparation. In instances where biologic widthviolation is suspected, the appropriate treatmentshould be performed, such as orthodontic extru-sion or osseous resection. In cases when an eden-tulous ridge requires surgical intervention forcreating an ovate pontic site, healing is confirmedby epithelialisation of the area (Figs. 7.3 & 7.4),and, where necessary, periodontal plastic surgery

Figure 7.1 Ideal tooth preparation with adequate resistanceand retention, smooth surface finish and a sinuous outline.

Figure 7.2 Healthy periodontal tissue around preparedtooth with knife-edge FGM and stippling of the attachedgingiva.

Figure 7.3 Ovate pontic created for missing lateral incisor.

Therapeutic temporary restorations 147

and/or adjustments to the temporary pontic aremade accordingly. Finally, splinting temporarycrowns reduces mobility, pending periodontaltherapy or extractions.

Function

A temporary restoration is an invaluable tool forassessing, maintaining or alerting occlusal andphonetic aberrations. This is particularly rele-vant when the abutment tooth makes initialcontact in centric relation, is a guiding tooth, aworking or non-working contact, when theocclusal scheme is changed or the vertical dimen-sion is altered. Furthermore, mandibular func-tion is verified for lateral and protrusive (anteriorguidance) contacts, as well as freedom of move-ment and masticatory function. The temporaryshould not inadvertently cause pressure on adjacent or opposing teeth, causing unwantedorthodontic movement or occlusal trauma, re-spectively. Besides occlusion, speech impedi-ments are also easily modified by removal oraddition to the temporary, avoiding costly andtime-consuming post-operative remakes. For adetailed occlusal and phonetic assessment, seeChapter 2.

Aesthetics

Many clinicians advocate, and expend enormousclinical time, creating nuances in colour andcharacterisations for a temporary prosthesis. The underlying premise of this onerous task isgaining instant patient gratification, and indi-rectly marketing the practice to the patients’family, friends and colleagues. Whilst matchingthe basic shade of the temporary restoration sothat it is inconspicuous is essential, spendingenormous clinical time creating nuances incolour and characterisation should be resisted.The reasons are as follows. Firstly, colour andcharacterisations are almost impossible to deter-mine accurately with temporary restorationsbecause the optical properties of the materialsused for temporary and definitive restorationsare dissimilar. Secondly, the physical propertiesof acrylics and porcelains vary enormously withrespect to wear, staining, plaque accumulation,surface texture and roughness, which affect lightinteractions and hence appearance. Therefore,the time spent refining colour can be betterutilised for aesthetic items that can be incorpo-rated into the definitive restorations, such asform and shape (Figs. 7.5–7.8).

Morphological variations are the aestheticitems, which can and should be assessed during

Figure 7.4 Tissue sculpturing with an acrylic therapeutictemporary restoration (bridge) 3 weeks later, showing epithe-lialisation of the ovate pontic site (compare with Figure 7.3).

Figure 7.5 Defective composite filling in left maxillarycentral incisor.


the temporarisation stage. These include intra-oral and extra-oral relationships. The intra-oralfactors include the general shape of the toothdetermined by the dental bioform or degree of gingival scallop (triangular, oval or square),contact points to ensure extent of papillary fill(Fig. 7.9), incisal embrasure angles, degree offacial and palatal contours, diastemae, imbrica-tions, axial inclination, sagittal inclination andhorizontal and vertical overbites.

The extra-oral relationships are tooth expo-sure (incisal edge position) during a relaxed andexaggerated smile, dental midline location, lipsupport and parallelism of the incisal plane to theinterpupillary line and curvature of the mandibu-lar lip (Figs. 7.10–7.12). Another issue is incor-poration of patient’s wishes, which are addressedat this stage (Figs. 7.13–7.17). Once these fac-tors are finalised, an impression is made of thetemporary crowns in situ, serving as a templateand communication tool for liaising with theceramist during fabrication of the definitive prosthesis.

When pre-prosthetic orthodontic movement isnecessary, temporary restorations are used forassessing gingival contour and contact points for interproximal papilla fill, thus eliminatingunsightly open gingival embrasures or ‘black triangles’. In addition, following orthodonticmovement, it is essential to confirm tooth andrelated gingival contour in three dimensions:

Figure 7.6 Tooth preparation for patient in Figure 7.5.

Figure 7.7 Chairside therapeutic temporary restoration onleft central is shorter than contralateral central incisor.

Figure 7.8 Addition of acrylic resin to finalise shape, whichwill act as a template for the definitive all-ceramic crown.

Figure 7.9 The contact point is too coronal to allow com-plete papilla fill between the temporary crowns on the max-illary centrals.


Figure 7.10 Frontal dentofacial view of temporary crown onright maxillary central to assess incisal edge position.

Figure 7.11 Lateral dentofacial view of temporary crown onright maxillary central to assess incisal edge position.

Figure 7.12 Facial view of temporary crown on right max-illary central to assess incisal edge position.

Figure 7.13 Tooth preparation for a three-unit FPD, abut-ments right maxillary central incisor and left lateral incisor,with ovate pontic for missing left central.

Figure 7.14 One of four sets of acrylic temporary bridgesused to finalise aesthetics, before proceeding to the definitivebridge for the patient in Figure 7.13.



apico-coronal, mesio-distal and sagittal (bucco-lingual) planes.

Aesthetics is not solely limited to the prosthe-ses. The contour, position, colour and texture of the surrounding gingival architecture are pre-requisite for aesthetic appraisal. Temporaryrestorations, as well as achieving and maintain-ing periodontal health, are used to sculpture softtissues, greatly influencing the so-called ‘pinkaesthetics’ (Figs. 7.18–7.20).



Figure 7.18 Defective metal–ceramic crowns on maxillarycentral incisors, with traumatised, amorphous FGMs.

Figure 7.19 Following tooth preparations and fabricatingtherapeutic temporary restorations, gingival health is estab-lished, with gingival zeniths distal to the long axes of thecentral incisors (compare with Figure 7.18).

Figure 7.20 Definitive crowns for patient in Figures 7.18and 7.19 showing impeccable aesthetics and integration of the prostheses in a harmonious co-existence with the periodontium.


Biocompatibility

Any material used in the oral cavity should be biocompatible and non-cytotoxic to vitaltissues. The potentially hazardous constituent inpolymer-based temporary crown and bridgematerials is the unreacted free monomer, whichcauses pulpal and gingival irritation. Conse-quently, complete polymerisation is crucial toavoid traces of this residual monomer. Using heatand pressure accelerates the setting reaction andensures it is complete.

Strength

The biomechanical properties of temporaryrestorations, such as adequate rigidity andresilience, are essential for resisting occlusal andmasticatory forces, ensuring the restoration sur-vives until the delivery of the definitive prosthe-sis. Most proprietary products display uniquemechanical properties; even materials in a givengeneric class vary enormously, making compar-isons a daunting task.1 Hence, every productshould be individually evaluated for suitabil-ity. The properties, which are discussed belowinclude flexural strength, modulus of rupture,MOE, microhardness and fracture toughness. In order to increase the strength of temporarymaterials, numerous reinforcement fillers havebeen suggested, such as metals, glass, carbon and nylon fibres. While these increase the MOE,it is crucial that a viable bond exists between the matrix and reinforcement inclusion. If not,the filler acts as an inclusion body weakening the material. Also, when a resin is reinforcedwith fibres, the later should be totally immersed within the matrix. Any protrudingfibres are difficult to polish, and attract fooddebris, encouraging bacterial colonisation.Finally, repairing a broken restoration drasticallyweakens the material. For example, bis-acrylmaterials exhibit as much as 85% reduction in strength compared with the initial intactrestoration.2

Palliative

Palliation of the underlying tooth abutment isachieved, firstly, by protecting the exposeddentine with DBAs following tooth preparation,thereby mitigating post-operative sensitivity, andsecondly, by preventing pulpal pathosis from theexothermic setting reaction of temporary crownmaterials.

Tooth preparation is a surgical procedure of hard dental tissues, resulting in exposeddentine tubules. If this naked dentine remainspatent and unprotected, post-operative sensitiv-ity is a common sequel causing distress and discomfort to the patient. The experienced sensitivity is explained by Brannstrom’s hydro-dynamic theory. This stipulates that fluid movement in the dentine tubules and the pulpchamber stimulates nerve endings which mani-fests as pain.3 The situation is compoundedfurther by bacterial invasion or toxin irritationdue to microleakage. Consequently, in order tominimise these hydrodynamic changes andprevent microleakage, the dentine tubulesrequire either sealing or blocking.

Tooth preparation with diamond burs pro-duces a thicker smear layer compared to usingsteel burs. The reason is that diamonds removeenamel and dentine by a grinding action, creat-ing more debris. Conversely, steel burs have acutting action, which results in a thinner smearlayer. The first step for dentine sealing is remov-ing the smear layer. The most predictable methodis by using a fifth generation DBA, sequentiallyetching with phosphoric acid, followed by pri-ming and sealing the dentine with an adhesiveresin to form the hybrid layer. Alternately theentire process, etching, priming and sealing, canbe carried out using sixth or seventh generation,self-etching, all-in-one DBA (Fig. 7.21). TheseDBAs are relatively new, and their efficacy isunconfirmed by long-term clinical data. Whichever BDA is chosen, it is important that it con-tains a dentine desensitiser and disinfectant suchas glutaraldehyde, e.g. Gluma (Heraeus Kulzer,Hanau, Germany). Rather than sealing, anothermethod is blocking dentine tubules, thereby pre-venting hydrodynamic fluid movement. Products


used for this technique include BisBlock (Bisco,Il, USA), which forms oxalate crystals within thetubules, halting fluid movement and alleviatingpost-operative sensitivity.

Most materials used for fabrication of tempo-rary restorations polymerise by an exothermicreaction. The temperature rise during the settingreaction of different materials varies from4.4–48°C, attributed to not only the exothermicreaction but also the energy absorbed duringirradiation of light-cured resins.4 In a seminalstudy on rhesus monkeys, a temperature eleva-tion of 5.5°C resulted in 15% irreversible pulpaldamage, an 11°C increase in 60% damage and a16.6°C increase in 100% pulpal necrosis.5 There-fore, the critical threshold for pulpal damage,which may be immediate or prolonged, is a tem-perature increase of 5.5°C. The temperatureincrease of intra-oral temporary crown materialsranges from 4–11°C, precarious to pulpal health.Consequently, it is imperative to minimise tem-perature rises during fabrication to safeguardpulp vitality.

The factors contributing to thermal insulationare the thickness of remaining dentine barrier,6

the hybrid layer width, the size of DBA adhesivelayer and luting or cement base.7 The thicknessof the hybrid layer (0.5–10µm) and the overly-ing adhesive layer (5–10µm) are inadequate forpreventing thermal insult. Furthermore, whilesealing dentine tubules with a DBA alleviatessensitivity and retards bacterial ingress, it offers

little thermal protection.8 Finally, intra-pulpaland periodontal blood supplies also dissipatetemperature increases by heat convection.

To summarise, the clinically pertinent points tomitigate intra-pulpal temperature rise are mate-rial selection, material volume, type of matrixform and fabrication technique.

Marginal integrity

Obtaining a hermetic seal of the temporary res-toration with the prepared teeth prevents micro-leakage, retards bacterial ingress that causespost-operative sensitivity, secondary caries,endodontic embarrassment, periodontal inflam-mation and leaching of provisional cements.

The average clinically accepted norm for mar-ginal opening (MO) of definitive restorations is50µm, and a similar accuracy is desirable for a temporary crown (Fig. 7.22).9 The MO isdependent on the intrinsic properties of the mate-rial and fabrication techniques. The major factoraffecting MO is polymerisation shrinkage,apparent with most polymer-based temporarycrown materials. The mean MO for temporaryresin materials ranges from 24–120µm, in-dicating that material selection is essential tominimise the potential restorative/tooth interfaceopening.10 Polymerisation shrinkage is time and

Figure 7.21 Application of a DBA immediately after toothpreparation.

Figure 7.22 A large MO is evident at the palatal margin ofthis bulbous crown.


temperature dependent. The majority of shrink-age of polymer-based materials occurs in the first5–10 minutes after mixing, a period which iscrucial during fabrication of temporary resto-rations. Additionally, elevated ambient tem-peratures increase the speed, rather than themagnitude of polymerisation shrinkage-strain.The magnitude of shrinkage is dependent onfactors such as filler volume (high filler equatesto low shrinkage), filler particle size, amount andtype of monomer, modes of polymerisation anddelayed water sorption.11 The clinical relevanceis that the polymerisation should be completedwithin 10 minutes of mixing, and familiarity ofthe handling characteristics of a specific materialwill circumvent unwanted shrinkage.

Preventing plaque accumulation

The major causative factor for gingival inflam-mation is plaque accumulation, and this is in-fluenced by the artificial restoration and thepatient’s oral hygiene regime. Combined, thesetwo factors determine whether gingival health ispossible and prolonged.12 The criteria affectingplaque accumulation on a temporary restorationare marginal integrity, surface roughness, emer-gence profile and overall shape and form of theprovisional, which should be conducive fordeflecting food and bacteria.

Following prophylaxis, a natural tooth soonforms a biofilm composed of salivary glycopro-teins. This pellicle promotes bacterial coloni-sation, and, if allowed to mature, becomespathogenic. Plaque accumulation is more abun-dant on artificial restorations compared withenamel and dentine.13 Consequently, the poten-tial for periodontal inflammation with artificialprostheses is elevated. The reason for this is pro-nounced plaque adhesion due to rough surfacessuch as defective margins, cement remnants andsurface irregularities (Fig. 7.23). In addition,methods of polishing also affect the degree ofaccumulation. Methods of decreasing plaqueaccumulation are contouring with aluminumoxide discs or steel burs, pumice abrasion, pol-

ishing with silicone tips and surface sealing withan unfilled resin. For example, using a surfacesealant, such as Biscover (Bisco, Il, USA), devoidof an oxygen inhibition layer, seals superficialirregularities following the finishing and polish-ing procedures.

The overall contour and form of a crownshould be curvaceous, free of sharp line anglesand free of microscopic grooves, with a smoothmicrotopography, helping deflect food particlesand discouraging plaque adhesion. A favourablecontour also facilitates cleansability and oralhygiene regimes.

Lastly, the emergence profile (EP) also influ-ences gingival health.14 The EP of a restorationis the cervical part, which meets the tooth apicalto the preparation finish line. This tooth/restora-tive interface should ideally lie on a tangent (Fig. 7.24). The EP should be linear in both thevertical and horizontal planes. A verticallyunder-contoured margin creates a niche for bac-teria, causing inflammation or caries (Figs.7.25–7.28), whereas a vertically over-contouredmargin violates the biologic width. In the hori-zontal plane, an under-contour results in anunsupported, flaccid FGM harbouring bacteria,inaccessible to prophylactic measures, while ahorizontal over-contour causes inflammationand restricts complete temporary cementremoval due to limited accessibility (Figs.7.29–7.31).

Figure 7.23 Marginal inflammation and periodontal abscessassociated with defective crown margins of prosthesis on leftcentral incisor.


Figure 7.24 Emergence profile of crown should lie on atangent with the root surface apical to the finish line.

Figure 7.25 Vertically under-contoured crown case study:the vertically under-contoured crowns of the maxillary cen-trals are a potential niche for bacteria.

Figure 7.26 Vertically under-contoured crown case study:tooth preparations with correctly located crown margins.

Figure 7.27 Vertically under-contoured crown case study:definitive crown-to-preparation relationship.

Figure 7.28 Vertically under-contoured crown case study:cemented Empress 1 crowns with correct emergence profiles(laboratory work by David Korson, UK).

Figure 7.29 Horizontally over-contoured crown case study:gross marginal inflammation around horizontally over-con-toured temporary crown on right maxillary central incisor.


Chromatic stability

As previously stated, it is unwise and futileattempting to ascertain the correct shade with atemporary restoration. Most temporary materi-als are chromatically unstable due to porosity,surface roughness, plaque accumulation, stain-ing, incomplete polymerisation and absorptionof oral fluids. Therefore, whilst it is aestheticallydesirable to fabricate a provisional whose colourapproximates to adjacent natural dentition, it isinadvisable to use this prototype as a guide forthe shade of the final restoration (Fig. 7.32).

Handling characteristics and ease of fabrication

Clinical manipulation of a temporary restorativematerial is essential to expedite fabrication. Eachmaterial is unique with regard to handling char-acteristics and this necessitates modification ofclinical techniques for optimal and consistentresults. Even within a given generic class, pro-prietary materials often display erratic charac-teristics that are specific to a given product.Material selection therefore becomes essentialfor ensuring that the requirements discussedabove are satisfied.

Material selection

Numerous factors influence the selection ofmaterials for a temporary restoration, includingthe anticipated duration of the prosthesis, aes-thetics, occlusal loads, repairability, ease ofmanipulation, number of units and whetheradjunct treatment is required, e.g. orthodontic,periodontal or endodontic. No single materialsatisfies all criteria, and, in many instances, acompromise is necessary. Alternatively, combina-tions of materials can be used for fabricatingtemporary restorations, exploiting beneficial

Figure 7.30 Horizontally over-contoured crown case study:crown removal shows circumferential halo indicating thatcrown margins are resting on marginal gingiva, not on theprepared tooth.

Figure 7.31 Horizontally over-contoured crown case study:replacement definitive Empress 1 crown with a correct emer-gence profile, allowing gingival health to be established (lab-oratory work by David Korson, UK).

Figure 7.32 Acrylic resin readily stains, and is not appro-priate for shade analysis for the definite prosthesis, as shownby the discoloured temporary crown on the right maxillarycentral incisor.


properties of different generic classes of prod-ucts. Most materials used for making temporarycrowns and bridges are resin based, which arechemical-, light- or dual-cured. For ease of han-dling, many are available in dispensing cartridgesensuring consistency of mix and disposability.The list below discusses some contemporarymaterials, citing advantages and limitations, andtheir suitability for specific clinical scenarios.

Polymethyl methacrylate (PMMA)

Most indirect temporary restorations are fabri-cated using this generic class of materials. Theyare the oldest acrylics used in dentistry, and wereonce advocated for definitive restorations, eitheralone, or with a metal substructure. The labora-tory process of heat and pressure curing alsoenhances the physical and mechanical properties.Hence, the main advantages are good mechani-cal properties, e.g. flexural strength and frac-ture toughness and excellent aesthetics.15 Thedisadvantages are a highly exothermic settingreaction, making intra-oral use prohibitive. Inaddition, the residual monomer is a pulpal irri-tant, while pronounced polymerisation shrink-age compromises margin integrity. To negatethese undesirable properties, PMMAs are used in small volumes to minimise shrinkage, e.g.PMMA shells made in the dental laboratory,which are subsequently filled and relined withpolyvinyl ethylmethacrylates (PVEMAs) directlyon the prepared tooth abutment. This procedureexploits the strength and aesthetics of PMMAs,while overcoming the shortfalls of polymerisa-tion shrinkage for a superior marginal seal (Figs.7.33 & 7.34).

Polyvinyl ethylmethacrylate (PVEMA)

Of the acrylics, PVEMAs are an ideal choice forintra-oral use, due to a lesser exothermic reac-tion, e.g. Trim (HJ Bosworth Co., Il, USA) andSNAP (Parkell, NY, USA) (Figs. 7.35 & 7.36).The monomer of ethyl methacrylate has reducedtoxicity compared to PMMAs. However, poros-ity compromises strength and aesthetics, and, if

Figure 7.33 Laboratory-fabricated acrylic crowns for maxil-lary incisors.

Figure 7.34 The temporaries in Figure 7.33 were relined atchairside to improve marginal fit before cementing with aprovisional luting agent (notice cervical additions).

Figure 7.35 Defective crowns on maxillary right lateral,central incisors and left lateral incisor.


worn for long periods, the surface discolours andstains are readily conspicuous. The mechanicalproperties are also mediocre, and the lower frac-ture toughness often predisposes to unwantedfractures. Repair of fractures and filling air blowsor voids is relatively simple by additions of a lowviscosity mix, or alternatively a flowable light-cured resin composite. Nevertheless, as statedabove, a repaired restoration is significantlyweaker than the original intact prosthesis.

Bis-GMA resin

The benefits of bis-GMA resins are similar to those of conventional restorative filling mate-rials made of the same compound, including malleability, large choice of shades and ease offabrication. They are available as light- and dual-cured varieties. The strength is intermediate com-pared to acrylics, with fracture toughness greaterthan PVEMA but lower than PMMA.16 Themain disadvantage is brittleness, causing minoror catastrophic fractures, especially if used formultiple splinted units.

Bis-acryl resin composite

The bis-acryl composite materials are probablythe most popular and widely used materials forintra-oral temporary crowns, e.g. Protemp (3M-

ESPE, St Paul, Minnesota, USA). Material pre-sentations include cartridge delivery (eliminatingmixing), variety of shades and various settingmodes (chemical-, dual- and light-cured), whichall expedite chairside fabrication. The benefitsinclude resistance to wear due to increasedmicro-hardness, high modulus of rupture andMOE. There is average fracture toughness.17

Polymerisation shrinkage is less than PMMAs,with lower temperature elevation during setting,and low pulpal irritancy. The major disadvan-tages are difficulty relining margins, poor pol-ishability and, hence, compromised aesthetics.Indications include single units, or short spansfor short duration.

Urethane dimethacrylate (UDMA) resin

UDMA is the ubiquitous resin matrix for manycontemporary composite filling materials. Themajor difference between the restorative andtemporary material is that the latter is not loadedwith filler particles and therefore has increasedflowability, e.g. Triad, (Dentsply, Germany). TheUDMA resin has high fracture toughness andlow exothermic reaction. The heat generated isnot from the setting reaction (as with acrylics),but due to radiation absorption during curingwith a visible light source. Furthermore, pulpalirritation is almost eliminated due to the absenceof a monomer. The disadvantages are poor mar-ginal integrity and polishability, resulting in infe-rior fit and aesthetics, respectively. However, toovercome poor aesthetics, a universal hybridrestorative material (with filler loading) can beused to veneer the temporary crown. This tech-nique is also beneficial using PVEMA as a coreand veneering with a hybrid composite.

CLINICAL PRACTICE

Fabrication

The dental literature is crammed with techniquesfor fabricating temporary restorations and ingen-

Figure 7.36 Chairside acrylic temporaries for patient inFigure 7.35 with improved marginal integrity.


ious methods are proposed depending on clini-cal scenarios. It is important to realise from theoutset that technique is paramount, supersedingthe choice of a given class of temporary materialor a specific proprietary product. Essentially,techniques can be categorised as direct (chairside fabrication) or indirect (constructed in a dentallaboratory). The direct method is instant andeconomical, but time consuming, and oftenresults in restorations with poor physical andaesthetic properties. This method is indicated fora limited number of teeth, up to three units, forshort duration of wear. The indirect methodoffers superior aesthetics and is ideal for pro-longed wear due to mechanical resilience (plusthe option to reinforce with metal or fibres), butwith increased costs. A combination technique isalso possible, exploiting the advantages of bothdirect and indirect methods, while overcomingtheir limitations.

Successful fabrication of TTRs involves twoentities: the external contours and internal con-tours. The factors influencing external contoursare tooth morphology, which depends on dentalbioform, gingival architecture, aesthetics, occlu-sion, contact points and phonetics. The inter-nal contours (or adaptation) are determined bytooth preparation geometry, including retentionand resistance form, surface roughness, type ofmargin finish line, preparation outline, and pres-ence or absence of undercuts.

Matrices

The external contours of TTRs are achievedusing matrices, categorised as:

� Existing anatomical form� Proposed anatomical form� Preformed anatomical form

Table 7.1 summarises the criteria for choosinga matrix.

Existing anatomical form

If the existing tooth morphology is acceptable, itcan be used as a template for the TTR. An algi-nate or electrometric impression is made for cre-ating the anatomical form (external contours). Asilicone impression, rather than an alginate, ispreferred since the former is dimensionallystable, can be stored, and is reusable if a remakeis necessary.

Proposed anatomical form

In many instances the reason for providing indi-rect restorations is to alter aesthetics, occlusionand function, which consequently requires mod-ification of existing tooth morphology. This is

Table 7.1 Criteria for choosing a matrix.

Criterion Existing Proposed Preformedanatomical form anatomical form anatomical form

Status quo Yes No NoAltering aesthetics, occlusion and OVD No Yes NoUnits Up to three Unlimited SingleDuration of wear Short Long ShortTTR material choice Limited Any LimitedExpediency Yes No YesCost Low High Medium


carried out either intra-orally or in the dentallaboratory. If minor changes are necessary,hybrid/flowable composite or wax is added untilthe desired shape is achieved. Alternatively, forextensive changes, a diagnostic wax-up of theproposed anatomy is fabricated in the dental lab-oratory (Figs. 7.37 & 7.38). An impression isthen made of the wax-up using a silicone mate-rial ensuring that adjacent teeth, as well as sur-rounding 1–2mm of soft tissues are recorded forprecise intra-oral location of the matrix. Theadvantage of using a silicone matrix is heat dis-sipation during the polymerisation of the tem-porary restorative materials. The disadvantage is

difficulty locating the silicone impression andtray on to the prepared teeth intra-orally, due tolack of transparency.

Another method is to pour a plaster cast of theimpression of the diagnostic wax-up and fabri-cate a vacuum-formed polypropylene matrix.The latter matrix can only be formed on a stonereplica of the wax-up, since the heat generatedduring vacuum forming would melt the diagnos-tic wax-up. Since the matrix is transparent,precise location on to the prepared teeth is facil-itated. Another benefit is that visible light-curedtemporary resin material can be utilised. Themajor disadvantage is that the thin shell is notan effective heat sink for materials with exo-thermic reactions.

Preformed metal and plastic crown forms

Prefabricated crowns are available in metal (alu-minum or stainless steel) or plastic (acrylic orpolycarbonate). Both types require filling with aresin for internal adaptation of the preparedtooth abutment. The metal varieties offer rigid-ity and durability, but require extensive shapingto conform to the occlusion and to obtain accu-rate margins. In addition, trimmed steel marginscan act as a scalpel, lacerating the soft tissues.The plastic variety offers immediate aesthetics,but also requires prolonged clinical time forshaping and verifying margin integrity and occlu-sion. Another advantage of the clear plastic vari-eties is ease of location and the ability to uselight-cured temporary crown materials. As agenerality, preformed crowns are indicated forsingle units, and are worn for short periods.

Techniques

Having chosen and fabricated the appropriatematrix for the external contours of a TTR, thenext stage is forming the internal contours. Thisis achieved by using one or more of the above-mentioned materials. Numerous factors influ-

Figure 7.37 Pre-operative cast showing uneven incisalplane and poor width/length ratio of maxillary incisors.

Figure 7.38 Proposed diagnostic wax-up to improve aes-thetics for patient in Figure 7.37, which is used to fabricatelaboratory acrylic temporaries (see Figures 7.33 and 7.34).


ence the choice of material, depending on theclinical requirements of a TTR. Table 7.2 pres-ents guidelines for making the correct choicedepending on clinical requirement. However,rather than trying to master every material, it is prudent to familiarise oneself with a few products and obtain predictable and consistentresults.

There are three fundamental techniques forfabricating TTRs: direct, indirect and a combi-nation of direct–indirect. In the author’s experi-ence, the methods and materials described belowfor each technique produce predictable results.However, the clinician may wish to modify thesesteps, omitting superfluous steps or adding stagesto modify procedures to tailor them for specificclinical needs.

Direct technique

(1) Refine existing anatomy and aesthetics byadditions with a flowable composite (orwax) and trim with diamond burs, discsand silicone polishing tips. Alternatively, apreformed crown can be utilised for theexternal contours, omitting steps (2) and(3) below

(2) Block pronounced gingival embrasureswith wax

(3) Fabricate a matrix using a silicone impres-sion material, or a vacuum-formed sheet(from diagnostic wax-up) for short-spanbridges

(4) Carry out tooth preparation(5) Following tooth preparation, place matrix

on to the abutment and adjacent teeth, ver-ifying correct seating and location

(6) The prepared teeth should already be iso-lated with retraction cord, and any looseemanating strands are gently replaced intothe gingival crevice, to allow visualisationof the circumferential preparation finishline. This ensures that the marginal inte-grity is not compromised by adherence of the cord to the temporary restorativematerial

(7) Apply phosphoric acid etchant to removethe smear layer (Hint 7.1), followed by aDBA incorporating desensitisers or alterna-tively use a dentine tubule blocking agent.Whilst DBAs afford little thermal pro-tection to the underlying pulp, they dohowever alleviate post-operative sensitivityby sealing the tubules and preventing bac-terial ingress

(8) Lubricate the abutment, surrounding andantagonist teeth liberally with petroleumjelly, to reduce thermal insult to the pulpand protect the gingival tissues. This sepa-rating medium also prevents locking of therestoration on to the abutment and in thegingival embrasures

(9) Choose material for internal contours fromTable 7.2, e.g. a PVEMA such as SNAP, andmix according to manufacturer’s instruc-tions. The usual mixing time for SNAP atroom temperature is 2–3 minutes, and theflowable mixture is poured into the matrix(Hint 7.2)

(10) Place the SNAP-loaded matrix on to theabutment(s) ensuring correct seating andlocation

(11) Flush with water for cooling and reducingtemperature elevation

(12) Once the rubbery stage is reached (4minutes from the start of mixing), removethe matrix with the temporaries, trimexcess from undercuts and re-seat tempo-raries without the matrix on to the abut-ment(s), ask patient to close in centricocclusion for 30 seconds (Hint 7.3)

(13) Remove temporaries from mouth and allowextra-oral setting for another 2 minutesuntil rigid (Hint 7.4)

(14) Once rigid, check marginal integrity, emer-gence profile, occlusion, aesthetics andpassive seating. Marginal discrepancies and voids are filled by additional material,mixed to a lower viscosity with a dullappearance (indicative of monomer evapo-ration). Unduly liquid mixes are avoided,since they contain large volumes of unre-acted free monomer, which causes pulpaland gingival irritation. Alternately, voids


or alterations to the morphology can be corrected by additions with a flowable composite

(15) Carry out gross trimming with tungstencarbide acrylic burs at low speeds. Exces-sive high-speed diamond burs tend to meltrather than cut acrylic resin. Finer refine-ments to margins, anatomy and occlusionare performed with aluminum discs, sili-cone tips and chamois leather mops (Hint7.5)

(16) If relining of the internal contours is neces-sary, use a mix that is neither thin norliquid, to avoid irritation by any unreactedfree monomer

(17) The restoration is luted with fine particle zinc oxide eugenol cement with

sufficient rigidity, such as Temp Bond (Kerr, Michigan, USA). Varieties of eugenol-freeand clear cements are also available, pre-venting interaction with bonding agentsand enhancing aesthetics, respectively. Foracrylic laminates, spot etching the abut-ment with 37% phosphoric acid, and lutingwith a flowable composite (without bond-ing agent) is an alternative method for temporary cementation

(18) Once set, remove excess cement and re-traction cord with a sharp probe, and usedental tape or floss to remove interproxi-mal remnants

(19) Finally, irrigate of the margins with 0.2%chlorhexidine liquid to flush cement frag-ments and encourage gingival health.

Table 7.2 Criteria for selection of material for internal contours of a TTR.

Criterion PMMA PVEMA Bis-GMA Bis-acryl UDMA Reinforce

Intra-oral U S S S S CExtra-oral S C S C S SManipulation/handling S S C C C CAesthetics S C S C C CStructural integrity/resilience S C C C C SReparability S S C C C CExpediency C S S S S CCost C S S C S C

S – Superior.C – Compromise.U – Unacceptable.


Indirect technique

This technique is less laborious than it initiallyappears, and the benefits of superior aestheticsand physical and mechanical properties oftenoutweigh the additional time and cost.

(1) The external contours can be either the exist-ing teeth if the aesthetics are acceptable, or a vacuum matrix using a polypropylenesheet on a stone model of the diagnosticwax-up

(2) Carry out tooth preparations with a retrac-tion cord in situ so that the circumferen-tial finish line is clearly discernible. A clearvacuum matrix (placed onto the preparedteeth) is particularly useful for checking thattooth reduction is sufficient to accommodatethe restorative materials of the definitiveprosthesis (metal and/or porcelain)

(3) Make an impression, using a silicone impres-sion material, of the tooth preparation fol-lowing sealing the freshly cut dentine with aDBA or dentine tubule blocking agent

(4) The impression is cast using rapid settingstone by either the clinician, or an on-sitedental laboratory

(5) Block interproximal gingival embrasureundercuts with wax, and liberally lubricatethe preparations, adjacent and antagonistteeth and soft tissues with petroleum jelly

(6) The stone model of the preparations iscoated with a silicone-separating medium

(7) If the temporaries are intended for longduration of wear, reinforcement by metals,fibres or rods is incorporated within thePMMA resin

(8) The pre-operative impression or clearvacuum matrix is filled with a PMMA resin,cured by heat and pressure in a hydro flask

(9) Once set, follow steps 15–19 in the direct technique for finishing, polishing andcementing.

Direct–indirect technique

The direct–indirect technique exploits thestrength, physical and aesthetic properties of the

indirect method, while ensuring a precision fit bydirectly relining on to the intra-oral tooth prepa-ration. This technique for fabrication of TTRscombines both extra- and intra-oral stages, the first nine steps are performed in the dentallaboratory, and the remaining in the surgery.

(1) The external contours can either be animpression of the existing anatomy, or of aproposed anatomy (diagnostic wax-up)

(2) A plaster cast is poured of the existinganatomy or the diagnostic wax-up

(3) A vacuum-formed transparent matrix isfabricated from step (2) above

(4) Tooth preparation(s) are simulated on theplaster cast. This can also be used as a guidefor intra-oral tooth preparation, or a pre-operative diagnostic tool for assessing fea-sibility of a proposed treatment plan

(5) The stone model of the preparations iscoated with a silicone-separating medium

(6) If the temporaries are intended for longduration of wear, reinforcement by metals,fibres or rods is incorporated within thePMMA resin

(7) Shells of the external contours are createdeither by painting the inner surface of theclear vacuum matrix with a PMMA or acomposite resin, before heat and pressurecuring (Hint 7.6)

(8) Once cured, the temporaries are trimmedand polished (step (15) of direct technique)

(9) The transparent matrix and shells of theexternal contours are returned to the surgery

(10) The clinician carries out tooth prepara-tions, using the matrix as a guide

(11) Once completed, gingival embrasures areblocked and petroleum jelly applied to teethand soft tissues

(12) The shells are seated, ensuring correct loca-tion and filled with a PVEMA to create theinternal contours. The next stages are thesame as for the direct technique, steps(9)–(19). Constant irrigation with water isimperative to allow heat dissipation, sincethe thin shell(s) offer little heat convectioncompared to a silicone impression matrix.


References

1 Haselton, D.R., Diaz-Arnold, A.M. andVargas, M.A. (2002) Flexural strength of pro-visional crown and fixed partial dentureresins. J Prosthet Dent, 87, 225–228

2 Koumjian, J.H. and Nimmo, A. (1990) Evalu-ation of fracture resistance of resins used forprovisional restorations. J Prosthet Dent, 64,654–657

3 Camps, J., Pizant, S., Dejou, J. and Franquin,J.C. (1998) Effects of desensitizing agents onhuman dentine permeability. Am J Dent, 11,289–290

4 Lloyd, C.H., Joshi, A. and Mcglynn, E. (1986)Temperature rises produced by light sourcesand composites during curing. Dent Mater, 2,170–174

5 Zach, L. and Cohen, C. (1965) Pulp responseto externally applied heat. Oral Surg OralMed Oral Pathol, 19, 515–529

6 Tjan, A.H.L. and Dunn, J.R. (1988) Tempera-ture rise produced by various visible light gen-erators through dentinal barriers. J ProsthetDent, 59, 433–438

7 Voth, E.D., Phillips, R.W. and Swartz, M.L.(1966) Thermal diffusion through amalgamand various liners. J Dent Res, 45, 1184–1190

8 Usumez, A., Ozturk, A.N. and Aykent, F.(2004) The effect of dentine desensitizers onthermal changes in the pulp chamber duringfabrication of provisional restorations. J OralRehab, 31, 579–584

9 LaMar, F.R. (2004) Guest editorial. Microgapor macrogap: significance of the marginal dis-crepancy between implant crown and abut-ment. Int J Periodontics Restorative Dent,24(3), 207

10 Tjan, A.H.L., Tjan, A.H. and Grant, B.E. (1987) Marginal accuracy of temporarycomposite crowns. J Prosthet Dent, 58(4),417–421

11 Kim, S.H. and Watts, D.C. (2004) Polymeri-sation shrinkage-strain kinetics of temporarycrown and bridge materials. Dental Mat, 20,88–95

12 Sorensen, J. (1989) A rationale for com-parison of plaque-retaining properties ofcrown systems. J Prosthet Dent, 62(3),264–269

13 Glantz, P.O. (1969) On wettability and adhesiveness. A study of enamel, dentine,some dental restorative dental materials anddental plaque. Odontol Rev, 17(Suppl 20),1–124

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Hints and tips

• Hint 7.1 – Avoid desiccating the dentinefollowing etchant removal, which mayelicit pulpal inflammation

• Hint 7.2 – Allow the mixture to reach adull appearance, ensuring evaporationof the free monomer, and minimising itsassociated toxicity

• Hint 7.3 – To dissipate heat, someauthorities advocate the repeated ‘on-off’ technique until the material is rigid.Whilst this rationale is sound, repeatedseating results in a poor marginal fit,often necessitating relines. Furthermore,if the measures outlined above for heatinsulation are followed (silicone matrix,water cooling, isolation with petroleumjelly), undue damage to the pulp andsoft tissues is avoided

• Hint 7.4 – Placing the temporaries inboiling water or a stream of hot airaccelerates the polymerisation reaction,i.e. the speed, rather than the magnitudeof shrinkage. The total setting reactionshould be completed within 10 minutesof the start of mixing

• Hint 7.5 – Sealing with a surface sealantsuch as Biscover, which is devoid of theoxygen inhibition layer, emulates aglaze and seals surface discrepanciesfollowing the polishing procedures

• Hint 7.6 – The advantage of using acomposite resin is a vast shade range


15 Moore, B., Goodcare, C., Swartz, M. andAndres, C. (1989) A comparison of resins forfabricating provisional fixed restorations. IntJ Prosthodont, 2, 173–184

16 Gegauff, A.G. and Pryor, H.G. (1987) Frac-ture toughness of provisional resins for fixedprosthodontics. J Prosthet Dent, 58, 23–29

17 Ireland, M.F., Dixon, D.L., Breeding, L.C. andRamp, M.H. (1998) In vitro mechanical prop-erty comparison of four resins used for fabri-cation of provisional fixed restorations. JProsthet Dent, 80, 158–162

Introduction

Shavell coined the phrase ‘biological impres-sions’, to signify impressions that capture, withfidelity, healthy tissues in their natural habitat.1

Most indirect dental restorations are made withonly an impression as the unifying elementlinking the three protagonists, ceramist, patientand dentist (or CPD) (Fig. 8.1). The intrinsicqualities of an impression are to record as muchand as accurate detail as possible. This necessi-tates faithfully recording the prepared, adjacentand opposing dentition, together with the sur-rounding soft tissues. Whether an impression isfor a laminate, inlay, crown, bridge, denture orimplant, the objective is to reproduce accuratelya facsimile of anatomical structures as a mor-phological platform for fabricating the proposedrestoration. This implies that the tissues areneither escharotic nor necrotic.

Two types of biological impressions arerequired: dental and gingival. The dental biolog-ical impression is one that replicates abutmentteeth following preparation. By definition, thisrequires deflecting the gingival crevice to accom-modate an impression material that will repro-

duce the preparation margins for obtaining acorrect emergence profile. The gingival biologi-cal impression records the periodontium in anon-deflected state. The latter is made after fab-ricating the definitive restoration, at the try-instage, when the gingival tissues have recoiled totheir normal position. By locating the restorationon an untrimmed plaster model, the rendezvousof a restoration with the surrounding soft tissues is visualised. This allows assessment ofthe cervical transmucosal soft tissue support andcontact points. Following modifications, a non-violent coexistence between the two entities,restoration and soft tissues, is achieved.2


Making precise impressions depends on twovariables, the primary and secondary determi-nants. While there is only one primary determi-nant, without which an accurate impression isunattainable, there are numerous secondarydeterminants, which are discussed initially,

8Biological impressions


before considering the crucial primary determinant.

Secondary determinants

The following list is not exhaustive, but emphasises pertinent points of the secondarydeterminants.

Stock vs. custom trays

The rationale for using custom or special trays isto control dimensional stability, and hence min-imise polymerisation shrinkage. This was par-ticularly significant with earlier elastomericmaterials, but is less relevant with contemporaryformulations. The newer materials are relativelystable, exhibiting sufficient stiffness and rigidity.The advantages of custom trays are ease of loca-tion and seating in the oral cavity, patientcomfort by avoiding sharp tray flanges imping-ing into the sulci, and capturing posterior teethwithout the need to modify stock trays with waxor compound materials. As a general guideline,stock trays are acceptable for one to three units

in conjunction with a heavy-bodied or putty base(Fig. 8.2).

Inter- vs. intra-arch

Intra-arch impressions record an entire archincluding contralateral teeth (Figs. 8.3–8.6),while inter-arch impressions record the antago-nist dentition. The latter is carried out using‘triple trays’ and benefits include eliminating anopposing arch impression and bite registration.While the resulting impression records both theprepared teeth and occlusal registration, thetechnique is trying for both the clinician andceramist. Furthermore, inter-arch impressions

Patient

Ceramist DentistIMP

Figure 8.1 The impression is the key element linkingceramist, patient and dentist.

Figure 8.2 Rigid plastic stock trays are satisfactory formaking impressions for up to three units.

Figure 8.3 Full maxillary intra-arch impression.

Biological impressions 167

are limited to one or two units. Further disad-vantages include distortion of tray when thepatient occludes,3 verifying whether the teeth arein centric occlusion, and ensuring that at leasttwo teeth either side of the prepared abutmentare included.

If, however, the tooth to be restored has inter-ferences (working or non-working side), or is theinitial contact in CR or a guiding tooth, inter-arch impressions are essential to allow mountingon a semi-adjustable articulator.

Closed vs. open tray

The rationale for an open tray is that drilledholes in the impression tray act as vents forexcess material and air to escape. In theory, this is valid, but clinically there is little improve-ment of the resulting impression. Furthermore,since excess material has to be rapidly moppedafter tray insertion, there is increased patient discomfort, often eliciting a reflex gaggingresponse.

One vs. two stages

The basis of a two-stage impression is ensuringa solid platform for the subsequent wash stage.The procedure involves taking an initial impres-sion with putty (using a rigid metal or stocktray), usually separated by an acetate orpolypropylene sheet, in effect, to form a customtray. The second stage is injecting a light-bodiedwash over the prepared teeth and reseating thetray. The obvious disadvantages are incorrecttray location, lengthy procedure and protractedendurance for the patient. The advantage of theone-stage impression is expediency and guaran-teed correct seating, but timing is critical. Thewash must be placed simultaneously on to theabutment while the assistant mixes and loads the putty or heavy-bodied material. In addition,once mixed, the tray must be inserted immedi-ately to prevent the material reaching the elasticstage, which can flex the tray (if plastic) andproduce distortions.4

Figure 8.4 Full mandibular intra-arch impression.

Figure 8.5 Trimmed dies from maxillary intra-arch impres-sion in Figure 8.3.

Figure 8.6 Completed crowns for patient in Figure 8.5.


Passive vs. non-passive

Most elastomeric materials recoil after the trayis removed from the mouth. A non-passiveimpression made by continuously applying pressure to the tray while the material is setting,causes pronounced recoil, with the detrimentalmanifestation that the crown fits the plaster die, but not the intra-oral abutment. To cir-cumvent the latter, once the tray is correctlyseated, pressure is relieved, allowing the materialto set passively. Since the material polymeriseswithout external pressure with a passive im-pression, post-removal recoil is significantlyreduced.5

Warm vs. cold environment

When attempting impressions for multiple units,a prolonged working time is clearly desirable.Chilling an impression material facilitates this,but increases the viscosity with possible alter-ation or retardation of the material setting reac-tion. Recently, a new impression material hasbeen introduced, Flexitime (Heraeus Kulzer,Hanau, Germany), which facilitates a variety ofclinical situations. Because the setting reaction isinitiated by the warm oral ambient temperature,polymerisation only starts when the material isplaced in the mouth. The working time rangesfrom 30 seconds to 21/2 minutes, but setting isalways 21/2 minutes after tray insertion, allowingimpressions of single as well as multiple prepa-rations (Fig. 8.7).

Manual vs. automated mixing

Using mechanical or automatic mixing equip-ment ensures a homogenous, void-free mix,greatly enhancing the quality of the final impres-sion. A variety of materials, including poly-ethers and addition silicones, are available in cartridges for these machines. The only draw-back is the initial capital outlay for equipmentpurchase.

Physical vs. chemical gingival retraction

Physical retraction of the gingival creviceinvolves using retraction cord(s) (Fig. 8.8). Thisis an effective and predictable method for achiev-ing transient opening of the sulcus, allowing animpression material to record the preparations’margins (Fig. 8.9). In addition, gingival retrac-tion is less traumatic than electrosurgery orrotary gingival curettage, with diminishedchances of ensuing gingival recession.6,7 How-ever, excessive pressure during cord placementmay inadvertently damage the delicate epitheliallining of the crevice or violate the biologic width.

Figure 8.7 Flexitime (Heraeus Kulzer) full maxillary archimpression.

Figure 8.8 Retraction cord being placed around preparedteeth.


Another concern with retraction cords is usinghaemostatic agents. Recent research concludesthat using the commonest haemostatic agents,such as racemic epinephrine, aluminum sulphate,aluminum chloride, aluminum potassium sul-phate or ferric sulphate, has no effect on settingreactions of polyvinyl siloxanes (addition sili-cones).8 Additionally, aluminum chloride is effec-tive for achieving chemical and mechanical tissuedisplacement,9 whereas epinephrine causes localnecrosis and possible unwanted systemic sideeffects.10

A recently introduced chemical retractionagent (Expasyl, Kerr) combines aluminium chlo-ride and kaolin. The aluminum chloride acts asthe astringent, while the hygroscopic kaolinexpands once in contact with crevicular fluid forachieving the desired gingival deflection. Whilstcircumferential enlargement of the sulcus isachieved, subsequent removal of the material byrinsing can be problematic. Lastly, chemicalretraction alone does not offer a physical barrier,as with retraction cords, for safeguarding thebiologic width.

Impression materials

The dental market is awash with impressionmaterials and selection depends on the intendeduse of the impression. Irreversible hydrocolloidsmay be acceptable for diagnostic or opposing

arch impressions, but are inappropriate for pre-cision-fabricated restorations. The properties offive commonly used impression materials forprosthodontics are summarised below and inTable 8.1.

Figure 8.9 Retraction cord in situ to deflect gingival creviceand act as a physical barrier protecting the biologic width.

Definitions

� Tear resistance – ability of an impres-sion material to resist tearing in smallcross sections, especially intra-sulcularareas

� Elastic recovery – the degree of recoilof a material without permanent elasticdeformations, e.g. from a tooth prepa-ration undercut

� Dimensional stability – ability to with-stand stress without permanent defor-mation, e.g. a heavy-bodied or puttyformulation

Reversible hydrocolloids

A decade ago, reversible hydrocolloids were thevogue. These materials are hydrophilic, allowingimpression making in a relatively moist environ-ment, and extremely accurate with good tearresistance. However, due to poor long-term stability, immediate pours are mandatory. Inaddition, a custom tray and heating/coolingapparatus are required, prolonging clinical timewith additional procedures. Another factor isthat multiple pours may not be feasible, andthese are necessary for most contemporary all-ceramic restorations.

Polysulphides

Polysulphides were the first elastomeric impres-sion materials, with excellent tear resistance,ideal for capturing subgingival crown margins.However, inferior elastic recovery necessitatedimmediate pours, while poor dimensional stabil-ity mandated using custom trays, both affectingthe accuracy of the impression.


Condensation silicones

These materials have enhanced elastic recoverycompared to polysulphides, but suffer from poortear resistance (Fig. 8.10). Hence, recording sub-gingival margins is trying and often results intorn material left in the gingival crevice, yieldinginaccurate margins.

Polyethers

Polyethers have superior tear resistance com-pared to condensation silicones, with excellentdimensional stability and accuracy. Anotherbenefit is the hydrophilic property, allowingimpressions to be made in relatively moist con-ditions. Initially, polyethers were unavailable ina heavy body, but newer formulations have puttycomponents, obviating the need for using acustom tray. Another disadvantage was rigidity,making removal from undercuts extremely difficult, e.g. locking into gingival embrasures

around periodontally compromised teeth. Thislimitation is also significant if multiple pours are necessary, since material rigidity causesbreakage of plaster casts upon removal of theimpression. The latest generations are ‘soft poly-ethers’ for increased patient comfort, and ease of

Table 8.1 Properties of popular impression materials.

Property Reversible Polysulphides Condensation Polyethers Addition siliconeshydrocolloids silicones

Tray Custom Custom Custom/stock Custom/stock Custom/stock

Handling Specific equipment Soft Soft Rigid, unpleasant Soft, multiple poursnecessary taste possible, avoid

Multiple pours? Multiple pours? latex gloves,11

and acrylic monomers

Hydrophilic Yes No No Yes No

Tear resistance Good Good Poor Good Average

Elastic recovery Average Average Good Good Good

Long-term Poor Poor Poor Good Goodstability

Disinfection Non-water soluble Water Water soluble Non-water Water soluble (e.g.soluble (e.g. soluble NaOCl)(e.g. NaOCl)NaOCl)

Immediate pour Yes Yes No No No

Accuracy Good Average Average Good Good

Figure 8.10 Condensation silicone impression (Optosil,Xantopren, Heraeus Kulzer).


retrievability from the mouth (Fig. 8.11). Newerversions are also insipid, eliminating the unde-sirable taste of older polyethers.

Polyvinyl siloxanes (addition silicones)

The most ubiquitous impression materials cur-rently used for prosthodontics are the additionsilicones. The large number of viscosities (Figs.8.12 & 8.13) makes these materials extremelyversatile for many clinical situations (Figs.8.14–8.19). The beneficial properties are excel-lent elastic recovery, dimensional stability, thematerials are tasteless and relatively soft (allow-ing removal from undercuts), stock or customtrays can be used and there is good detail

Figure 8.11 Polyether impression (P2, Heraeus Kulzer).

Figure 8.12 Addition silicones are available in a variety of viscosities: monophase, medium and light-bodied consistencies.

Figure 8.13 Sectioned impression and dies using three addi-tion silicone viscosities for patient in Figure 8.12.

Figure 8.14 Use of addition silicones: implant-supportedrestorations.

Figure 8.15 Use of addition silicones: single units.


reproduction (accuracy). The tear resistance ofaddition silicones is less than that of polysul-phides. However, a balance is necessary. The hightear resistance of polysulphides, but poor elasticrecovery, means that although the material willnot tear, it will permanently deform. Conversely,the addition silicones have good elastic recoveryand lower tear resistance, meaning that the mate-rial will tear before permanent deformation. The latter is crucial for accurately reproducing prepared abutments. These properties are amajor reason for their popularity for contempo-rary dental procedures.12 The main disadvantageis that polyvinyl siloxanes are intrinsicallyhydrophobic, but the recently introduced Provilnovo (Heraeus Kulzer, Hanau, Germany) claims to be ‘hydroactiv’, by initially ‘wetting’the abutment tooth, thereby overcoming thestringent arid environment necessary for addi-tion silicones.

Primary determinant

The above discussion has focused on the sec-ondary determinants influencing an accurateimpression. However, even if all these factors areoptimally prevalent, absence of the primarydeterminant makes an accurate impressionelusive. The single factor, which is quintessentialfor a precise impression, is attaining and

Figure 8.16 Use of addition silicones: indirect post/cores.

Figure 8.17 Use of addition silicones: multiple units.

Figure 8.18 Use of addition silicones: porcelain inlays.

Figure 8.19 Use of addition silicones: porcelain onlays.


maintaining periodontal health; this is termed the primary determinant (Figs. 8.20–8.22). Theperiod for gingival healing varies enormouslyfrom 3–21 days, and is influenced by patient andoperator factors.13

Patient factors (risk assessment)

� Genetic predisposition� Age� Gender, e.g. pregnancy, osteoporosis� Race� Systemic illness, e.g. diabetes, compromised

immune system, psychological stress14

� Dental biotype and bioform� Type of oral pathogens

� Local trauma, or previous pathology withcompromised vascularity, e.g. periapicallesions

� Socio-economic status� Oral hygiene� Local irritants, e.g. smoking, tobacco or

betel nut chewing

All the above factors are beyond the clinician’scontrol, and first nine are beyond the patient’scontrol.15 Although unchangeable, these riskfactors should be borne in mind since these affectthe rate of healing and may necessitate revisingthe proposed treatment plan (see discussion onrisk assessment in Chapter 1). For example, anelderly patient, with systemic ailments, will havea protracted healing time. Also, a thin scallopedbiotype will negate extensive soft tissue manipu-lation for fear of gingival recession, especially inaesthetically sensitive areas. Finally, low socio-economic status patients may not regard dentalcare a priority, and proposing sophisticated treat-ment modalities may be futile because of a high risk of failure (poor compliance and maintenance).

The last two items, oral hygiene and local irri-tants, are the only two factors that a patient canchange, and which the clinician can influence byoral health education, emphasising the impor-tance of maintaining a natural dentition.

Figure 8.20 Achieving periodontal health: pre-operativedefective crowns.

Figure 8.21 Achieving periodontal health: crown removal.

Figure 8.22 Achieving periodontal health: post/core build-up. Following tooth preparation and temporarisation, thegingiva is stable and healthy, ready for impression making.


Operator factors

� Prevention and prophylaxis, e.g. scaling andpolishing

� Biologic width integrity� Correct emergence profile� Atraumatic clinical protocols, e.g. non-

haemorrhagic procedures, calculated andprecise tooth preparation, accurate impres-sions and cementing techniques

� Therapeutic temporary restorations

The operator factors are entirely controllableby clinical decisions and protocols, influencingwhether or not periodontal health is achievedand maintained.

Prophylaxis

Scaling, polishing or root planing, with orwithout pharmaceutical adjuncts, are the firstprerequisites for achieving periodontal health.Often, these vital procedures are either omittedor ignored, due to the overwhelming desire forcommencing treatment. A little time spent at thestart is not only beneficial for long-term oralhealth, but expedites all ensuing clinical stages.An adequate time following thorough prophy-laxis is necessary to assess home oral hygienemeasures and verify gingival health (Figs.8.23–8.26). This also confirms the patient’sresponsibilities and commitment to the proposedtreatment. If, however, compliance during thisphase is poor, the treatment plan may require

Figure 8.23 Pre-operative calculus and plaque deposits.

Figure 8.24 Post-operative after scaling and oral hygieneinstruction of patient in Figure 8.23.

Figure 8.25 The left anterior mandibular teeth have beenscaled, showing gingival health (pink colour, stippling, knife-edge FGMs). Compare with the right side, which has depositsand inflammation.

Figure 8.26 The anterior mandibular and left maxillary teethhave been scaled. Compare with the right maxillary teeth,which have calculus and periodontal inflammation.


modification to less sophisticated options, inorder to avoid disappointments at later phases oftreatment.

Biologic width integrity

The biologic width is discussed in Chapter 2, andis nature’s way of protecting the two essentialelements which ensure the survival of a tooth: thealveolar bone and the periodontal ligament. Ifthese are compromised, the survival of the toothis jeopardised. A shield is obviously only effec-tive when intact. If damaged or destroyed, itsfunction is reduced or nullified. Hence, any insult to this shield, bacterial or iatrogenic,diminishes its ability to fulfil the intended func-tion. Clinical procedures potentially hazardousto the biologic width are retraction cord place-ment, tooth preparation, impressions, location ofcrown margins and cementation. Therefore, anyrestorative procedure either should be supragin-gival, or confined to dimensions of the gingivalsulcus for respecting biologic width dimensions.

If location of the crown margins is subgingi-val, it is necessary to verify the crevice depth, sothat impression procedures do not violate theepithelial attachment. Chapter 2 discussed therationale for either using the alveolar bone crest(ABC), or a healthy free gingival margin (FGM)as a reference point. If the ABC is used as a land-mark, the sulcus depth must be verified. Mea-suring pocket depths with a periodontal probe isinaccurate, because it is often difficult to assessthe position of the probe tip, which may havepenetrated beyond the crevice base into theepithelial or connective tissue attachments. Theprobe depth also depends on the force applied,tooth and probe angulations and prevalentinflammation. The ideal method to determinesulcus depth is to sound bone around an anaes-thetised tooth and measure the entire dentogin-gival complex. Assuming ideal tooth anatomicalvariables, a mid-facial reading of 3mm indicatesa sulcus depth of 1mm (entire dentogingivalcomplex = 3mm, minus 2mm for biologic width= 1mm sulcus depth). An interproximal meas-urement of 5mm, indicates a 3mm sulcus depth(entire dentogingival complex = 5mm, minus 2mm for biologic width = 3mm sulcus depth).

Alternatively, if the FGM is used, the crownmargins should be placed 0.5mm within thesulcus from the most apical zenith of the FGM,coronal to the epithelial attachment (Fig. 8.27).It is evident that whichever landmark is used,ABC or FGM, the margins are located coronalto the epithelial attachment. Similarly, theimpression procedures are also limited to thedimensions of the sulcus.

Another factor to consider is the periodontalbiotype, e.g. a thin, scalloped biotype will pre-dispose to gingival recession, while a thick, flatbiotype predisposes to periodontal pocket for-mation or persistent inflammation.16 For anteriorrestorations, delicate tissue manipulation is nec-essary with thin scalloped biotypes for avoidinggingival recession, which could compromise aesthetics.

Emergence profile

The emergence profile of a crown is the junctionof its cervical aspect, which meets the preparedtooth margin (Fig. 8.28).17 An ideal emergenceprofile is attained when the crown and toothmargins meet at a tangent. Or, put another way,the crown margin lies at 180° to the root surface,apical to prepared tooth margins, ensuring thatthe crown is neither over- nor under-contoured.If the TTR was correctly fabricated, gingivalhealth should be apparent. If the FGM isblanched or flaccid and unsupported, the gingiva

Figure 8.27 Periodontal probe measuring sulcus depth,using a healthy FGM as a reference point.


will be inflamed, and this requires resolutionbefore biological impressions are attempted (Fig. 8.29).

Atraumatic clinical protocols

Following prophylaxis and achievement of peri-odontal health and stability, all clinical proce-dures should be performed atraumatically,minimising soft and hard tissue damage. Theseinclude crown removal, tooth preparation,retraction cord placement, impression makingand cementation.18 Ideally, whenever possible, anon-haemorrhagic approach is adopted, with therationale that minimising trauma during treat-

ment not only accelerates the healing process,but also helps maintain existing health (Figs.8.30–8.34).

Therapeutic temporary restorations

A detailed explanation for fabricating tempo-raries is outlined in Chapter 7. To summarise, atemporary restoration should respect the bio-logic width, have a correct emergence profile andact as a template for the definitive restoration(Fig. 8.35). The fruits of these labours arerealised when attempting impressions. Meticu-lous attention to detail during fabricating,adjusting and maintaining a temporary prosthe-sis results in optimal soft tissue health, a prereq-uisite for both dental and gingival impressions.

Figure 8.28 Emergence profile: sagittal view of a crown sil-houette showing that its margins are on a tangent with theroot apical to the finish line.

Figure 8.29 Gingival inflammation around incorrectly con-toured temporary crown on left maxillary canine.

Figure 8.30 Atraumatic clinical protocol: pre-operativedefective crown on left maxillary lateral.

Figure 8.31 Atraumatic clinical protocol: retraction cord insulcus and crown removal.


CLINICAL PRACTICE

Once the primary determinant, gingival health,is attained and maintained, biological impres-sions are contemplated. Two types are required,the dental and gingival biological impressions.

Dental biological impressions

The dental biological impression is for recordingthe prepared tooth margins. To achieve this, gin-gival retraction using the double cord techniqueis necessary for exposing the preparationmargins, maintaining an arid environment andaccommodating an adequate bulk of impressionmaterial.19 In order to avoid distortion of theimpression material a minimum sulcus openingof at least 0.2mm is required,20 and typically, agingival deflection of 0.3–0.4mm is routine.21

Finally, it is necessary to record the apical partof the root beyond the preparation margins,allowing the ceramist to construct a correctcrown emergence profile. The double cord tech-nique is shown in Figure 8.36. The first thin cord(Ultradent # 000) is delicately introduced intothe sulcus to vertically retract the gingiva api-cally, and maintain a dry field by absorbing thecrevicular fluid. This cord should disappear into

Figure 8.32 Atraumatic clinical protocol: refined cast metalcore using a haemorrhage-free protocol.

Figure 8.33 Atraumatic clinical protocol: definitive crown-to-tooth preparation relationship.

Figure 8.34 Atraumatic clinical protocol: cemented defini-tive crown.

Figure 8.35 Chairside temporary acrylic crowns on teeth#12, 11 and 21, which will be adjusted and used as templatesfor the final restorations.


the sulcus and be invisible from the facial aspect.The second thicker cord (Ultradent # 1), pre-impregnated with an astringent, e.g. bufferedaluminium chloride, is introduced to half itswidth to transiently horizontally (laterally) openthe gingival crevice. Instead of using a pre-impregnated cord, a dry cord can be placed intothe sulcus, and then dabbed with astringent,which swells the cord and dilates the crevice.After 5 minutes, the second cord is removed,while the first stays in situ. An impression is nowpossible to record the preparation margins, andan apical part of the tooth beyond the finish line(Figs. 8.37 & 8.38).

To ensure predictable and consistently accu-rate impressions, the following sequence is necessary:

(1) Establish presence of primary determinant,i.e. gingival health

(2) Choose appropriate secondary determi-nates:� Stock tray for up to three units, custom

tray for more than three units� Full intra-arch impressions� Avoid excessively large holes in trays,

minimising intra-oral excess materialspillage (or use closed-tray technique)

� One-stage technique� Passive setting of impression material� Avoid chilling impression material� Use automixing units

� Use either retraction cord as a physicalbarrier in sulcus or chemical retraction

� Use either polyether or addition sili-cone materials for convenience, expe-diency and accuracy

(3) After tooth preparation (Fig. 8.39), sealexposed dentine tubules, mitigating post-operative sensitivity22 using either a sixth or seventh generation self-etching DBA23 ora fifth generation DBA by etching, primingand sealing. To avoid interaction of theoxygen inhibition layer with acrylicmonomer and impression materials, light-cure the bonding agent through a glycerinegel cover24

(4) Ascertain sulcus depth for selection of theappropriate diameters of the retractioncords. For the double retraction cord tech-nique, both cords are placed within thedimensions of the prevailing sulcus depth.The first cord is thinner than the secondcord

(5) Assuming normal anatomical relationships,the first cord is usually # Ultradent 000.Applying gentle pressure with a thin flatplastic instrument, introduce the dry cordinto the friable sulcus without causinghaemorrhage (Fig. 8.40) (Hint 8.1)

(6) Next, a second thicker cord, usually Ultra-dent # 1 pre-impregnated with an astrin-gent, e.g. buffered aluminium chloride, isplaced to half its width (Hint 8.2). Thissecond cord should be visible from thefacial aspect (Fig. 8.41) (Hint 8.3)

(7) After 5 minutes, ease second cord from thesulcus, leaving the first thinner cord in situ(Figs. 8.42 & 8.43) (Hint 8.4)

(8) Copiously apply tray adhesive to the appro-priate size tray (Hint 8.5)25

(9) While injecting the low viscosity wash onto the prepared abutment(s) (Fig. 8.44), askassistant simultaneously to load the heavy-body material into impression tray (Hint8.6)

(10) After correct seating and location of thetray, relieve pressure allowing passive poly-merisation of the impression materials(Hint 8.7)

(11) Once set, rapidly remove tray avoiding vis-coelastic distortions of impression materi-

CEJ

Sulcus0.69 mm

Epithelial attachment0.97 mm

Biologic width2.04 mm Connective tissue

attachment1.07 mm

Figure 8.36 Double retraction cord technique.


als. Rapid removal reduces the time thematerial is under stress and thereforereduces permanent distortions26

(12) Check impression for absence of voids anddefects, and faithful reproduction of thepart of the root surface apical to the prepa-ration margins (Hint 8.8)

(13) Disinfect with appropriate antiseptic solution, e.g. glutaraldehyde or sodiumhypochloride (Hint 8.9)27

(14) Pour impression using dental plaster/stone(addition silicones are compatible withmost dental plasters for model and die fab-rication) (Fig. 8.45)

(15) Addition silicones allow multiple pours forup to 1 week, and both addition siliconesand polyethers can be stored in temperatureranges of 4–40°C without affecting dimen-sional stability28

(16) Take facebow and bite registrations (Figs.8.46 & 8.47).

Gingival biological impressions

The gingival impression is for assessing the rela-tionship between soft tissues and the artificialprostheses. This impression is essential for ante-rior teeth where ‘pink’ or soft tissue aestheticsare of paramount concern, but less relevant for

Figure 8.37 Retraction cord in situ to deflect gingivalmargins for recording the root surface apical to the finish line.

Figure 8.38 Plaster cast of impression for patient in Figure8.37 showing that the area apical to the crown margins isaccurately reproduced, which will be used by the ceramist toobtain a correct emergence profile.

Figure 8.39 Double retraction cord technique for dentalbiological impressions: completed tooth preparations onmaxillary central incisors with a healthy periodontium.

Figure 8.40 Double retraction cord technique for dentalbiological impressions: the sulcus around the left central willbe deflected, while that on the right central will remain un-deflected for comparison. First thin, dry cord placed into thegingival crevice.


Figure 8.41 Double retraction cord technique for dentalbiological impressions: second thicker cord placed to half itswidth.

Figure 8.42 Double retraction cord technique for dentalbiological impressions: second cord removed after 5 minutes,leaving the first thinner cord in the sulcus.

Figure 8.43 Double retraction cord technique for dentalbiological impressions: retracted sulcus on left central incisor,compare with un-deflected sulcus around right central.

Figure 8.44 Double retraction cord technique for dentalbiological impressions: light-bodied impression materialplaced around preparations immediately following gingivalretraction.

Figure 8.45 Double retraction cord technique for dentalbiological impressions: plaster cast showing accurate record-ing of the root surface apical to the finish line.

Figure 8.46 Double retraction cord technique for dentalbiological impressions: facebow registration for semi-adjustable articulator.


posterior extra-coronal and all intra-coronalrestorations.

The gingival biological impression is madeeither at the bisque try-in stage of the definitiverestoration, or with the TTRs (Fig. 8.48). Thepurpose is recording undeflected, healthy gingi-val architecture in a natural resting state. Thisallows correct interproximal contact points (Fig.8.49), by contouring the crowns in relation to thebone crest, ideally 5mm or less for completepapilla,29 and ensuring ideal transmucosalsupport of the FGM by the cervical part of the

crown, preventing a horizontally under- or over-contoured crown.

Clinically, steps for a gingival impression aresimilar to the dental impressions. The essentialdifference with gingival impressions is thatretractions cords are omitted.

(1) Establish presence of primary determinant,i.e. gingival health

(2) Choose appropriate secondary determi-nates as for dental impressions

(3) A monophase consistency of either poly-ether or addition silicone is the ideal mate-rial for gingival biological impressions

(4) Ensure tooth abutment is clean and free oftemporary cement

(5) Place crowns (bisque stage definitives orTTR) on to prepared abutments

(6) Copiously apply tray adhesive to appropri-ate size tray

(7) Mix monophase impression material andload into tray

(8) After correct seating and location of the tray, relieve pressure, allowing passive polymerisation of the impressionmaterials

(9) Once set, rapidly remove tray avoiding vis-coelastic distortions of impression materi-als. Rapid removal reduces the time thematerial is under stress and thereforereduces permanent distortions

(10) Check impression for absence of voids anddefects

(11) The crowns should be picked up in theimpression, if not, remove from the abut-ment(s) and carefully seat into impression

(12) Disinfect with appropriate antiseptic solution, e.g. glutaraldehyde or sodiumhypochloride

(13) Pour impression using dental plaster/stone(addition silicones are compatible withmost dental plasters for model and die fab-rication or create soft tissue emulating thegingivae (Figs. 8.50 & 8.51)

(14) Addition silicones allow multiple pours forup to 1 week, and both addition siliconeand polyethers can be stored at tempera-tures of 4–40°C without affecting dimen-sional stability.

Figure 8.47 Double retraction cord technique for dentalbiological impressions: silicone bite registration.

Figure 8.48 Gingival biological impressions: crowns pickedup in a soft silicone impression material.


Figure 8.49 Gingival biological impressions: plaster castshowing that the gingival impression records the soft tissuesin a healthy, non-deflected state.

Figure 8.50 Gingival biological impressions: silicone softtissue model to contour transmucosal part of the crown.

Figure 8.51 Gingival biological impressions: correctly con-toured crowns for patient in Figure 8.50.

Hints and Tips

� Hint 8.1 – The first thinner cord shouldentirely disappear into the sulcus, andbe invisible from the facial aspect

� Hint 8.2 – The second, thicker cordshould be impregnated with the haemo-static agent 10–15 minutes before use

� Hint 8.3 – Instead of pre-soaking thesecond cord in a haemostatic agent, itcan be placed and soaked later withhaemostatic agent using cotton woolpellets. This protocol swells the cord,facilitating mechanical dilatation of thesulcus

� Hint 8.4 – Moistening the second cordwith water before removal preventsunwanted haemorrhage

� Hint 8.5 – Air-drying the tray adhesiveensures tenacity, and prevents poolingwhich causes the adhesive to act as alubricant rather than an adhesive

� Hint 8.6 – When mixing addition sili-cone putty manually, use vinyl insteadof latex gloves, which retard settingreaction

� Hint 8.7 – Using a timer or stopwatchensures precise intra-oral setting reac-tion, usually 3 minutes (depending onproprietary product)

� Hint 8.8 – If the first, thinner cord ispicked up in the impression, loose partscan be cut with scissors. However,attempting to pull tenacious cordembedded in the impression materialcauses tears, leading to inaccuracies ofthe crown margins or the area apical tothe margins; these areas are essential forcreating a correct emergence profile

� Hint 8.9 – Disinfecting for 30–60minutes results in no distortion, butlong-term, overnight soaking (>18hours) causes irreversible distortion ofthe impression material


References

1 Shavell, H.M. (1988) Mastering the art oftissue management during provisionalizationand biological final impressions. Int J Peri-odont Rest Dent, 8(3), 24–43

2 Touati, B. and Etienne, J.-M. (1998) Improvedshape and emergence profile in an extensiveceramic rehabilitation. Pract PeriodontAesthet Dent, 10(1), 129–135

3 Ceyhan, A.J., Johnson, G.H. and Lepe, X.(2003) The effect of tray selection, viscosity ofimpression materials, and sequence of pour onthe accuracy of dies made from dual-archimpressions. J Prosthet Dent, 90(2), 143–149

4 McCabe, J.F. and Carrick, T.E. (1989) Rheo-logical properties of elastomers during setting.J Dent Res, 68, 1218–1222

5 Sadan, A. (2001) The one-step versus the two-step impression technique. Pract ProcedAesthet Dent, 13(4), 282

6 Ruel, J., Schuessler, P.J., Malament, K. andMori, D. (1980) Effects of retraction proce-dures on the periodontium in humans. J Pros-thet Dent, 44, 508–515

7 Azzi, R., Tsao, T.F., Carranza, F.A. andKennedy, E.B. (1983) Comparative study ofgingival retraction methods. J Prosthet Dent,50, 561–565

8 de Camargo, L.M., Chee, W.W.L. andDonovan, T.E. (1993) Inhibition of polymeri-sation of polyvinyl siloxanes by medicamentsused on gingival retraction cords. J ProsthetDent, 70, 114–117

9 Weir, D.J. and Williams, B.H. (1984) Clinicaleffectiveness of mechanical-chemical tissuedisplacement methods. J Prosthet Dent, 51,326–329

10 Pelzner, R.B., Kempler, D., Stark, M.M., Lum,L.B., Nicholson, R.J. and Soelberg, K.B.(1978) Human blood pressure and pulse rateresponse to racemic epinephrine retractioncord. J Prosthet Dent, 39, 287–292

11 Kahn, R.L. and Donovan, T.E. (1989) A pilotstudy of polymerisation inhibition ofpoly(vinyl siloxane) materials by latex gloves.Int J Prosthodont, 2, 128–130

12 Tjan, A.H.L., Whan, S.B., Tijan, A.H. andSarkissian, R. (1996) Clinically orientatedevaluation of the accuracy of commonly usedimpression materials. J Prosthet Dent, 56, 4–8

13 de Gennaro, G.G., Landesman, H.M. andCalhoun, J.E. (1982) Comparison of gingivalinflammation related to retraction cords. JProsthet Dent, 47, 384–386

14 Torabi-Gaarden, R., Breivik, T., Hansen, F.,Malt, U.F. and Gjermo, P.E. (2004) Negativelife events, anxiety, depression and copingability (stress) as related to chronic periodon-titis. Perio, 1(1), 35–42

15 Wilson, T.G. and Kornman, K.S. (1996) Fun-damentals of Periodontics. Quintessence Pub-lishing Co. Inc., Carol Stream, IL

16 Olsson, M. and Lindhe, J. (1991) Periodontalcharacteristics in individuals with varyingform of the upper central incisors. J Clin Peri-odontol, 18(1), 78–82

17 Martignoni, M. and Schonenberger, A. (1990)Precision Fixed Prosthodontics: Clinical andLaboratory Aspects. Quintessence PublishingCo. Inc., Chicago

18 Ahmad, I. (2001) Replacing defective porce-lain fused to metal crowns with galvano-ceramic restorations as an alternative toall-ceramic crowns: a clinical case study. Inde-pendent Dentistry, November, 2001

19 Perakis, N., Belser, U.C. and Magne, P. (2004)Final impressions: a review of material prop-erties and description of a current technique.Int J Periodontics Restorative Dent, 24,109–117

20 Laufer, B.Z., Baharav, H., Ganor, Y. andCardash, H.S. (1996) The effect of marginalthickness on the distortion of different impres-sion materials. J Prosthet Dent, 76, 466–471

21 Ramadan, F.A. (1968) The Linear Effective-ness of Dental Tissue Displacement Materials.Thesis, St Louis University Dental School

22 Paul, S.J. and Scharer, P. (1997) The dualbonding technique: a modified method toimprove adhesive luting procedure. Int J Peri-odontics Restorative Dent, 17, 536–545

23 Ahmad, I. (2003) Evaluating dentine bondingagents: an update. Pract Proced Aesthet Dent,15(7), 531–538


24 Magne, P. and Belser, U. (2002) Immediatedentin bonding. In: Bonded PorcelainRestorations in the Anterior Dentition – ABiomimetric Approach. pp. 270–273. Quin-tessence, Berlin

25 Bindra, B. and Heath, J.R.I. (1997) Adhesionof elastomeric impression materials to tray. JOral Rehabil, 24, 63–69

26 Hondrum, S.O. (1994) Tera energy propertiesof three impression materials. Int J Prostho-dont, 7, 517–521

27 Rios, M., Morgano, S.M., Stein, R.S. andRose, L. (1996) Effects of chemical disinfec-tant solutions on the stability and accuracy of

the dental impression complex. J ProsthetDent, 76, 356–362

28 Corso, M., Abanomy, A., Di Canzio, J.,Zurakowski, D. and Morango, S.M. (1998)The effect of temperature changes on thedimensional stability of polyvinyl siloxaneand polyether impression materials. J ProsthetDent, 79, 626–631

29 Tarnow, D., Magner, A. and Fletcher, P. (1992)The effect of the distance from the contactpoint to the crest of bone in the presence orabsence of the interproximal dental papilla. J Periodontol, 63(1), 995–996

The try-in stage is the most interactive stage in the provision of artificial restorations, involv-ing the clinician, ceramist, dental nurse, hygien-ist, the patient and patient’s family and friends.Whilst biological and technical aspects are theconcerns of the clinician and ceramist, respec-tively, aesthetics and visual assessment by theentire dental team, the patient and theirentourage is invaluable for avoiding later disap-pointments and misgivings.

At the try-in procedure, the clinician has a lastchance to rectify a restoration prior to cementa-tion. Most aspects of the prosthesis should havebeen finalised with the therapeutic restorations,including occlusion, phonetics and aesthetics(form, size and position). While the latter can bere-assessed, some items can only be evaluated atthe try-in stage. These include correct die trim-ming, sufficient space for a cement vent by usingdie spacers, intaglio surface purity, unimpededseating, margin integrity, proximal contacts,emergence profile, cervical trans-gingivalcontour (horizontal and vertical under- or over-contouring), texture, lustre and colour with dif-ferent lighting conditions (Fig. 9.1).

Basically, two types of refinements may be nec-essary: material additions and removals. As ageneralisation, additions usually require aremake, whilst removals, if minimal, can becarried out chairside. If removals are required,these should be kept to an absolute minimum. Aspreviously mentioned, any adjustment to ceram-ics initiates flaws, which propagate to eventualfracture. This is particularly relevant for thincross-sectional or uni-layer ceramics, unsup-ported by high-strength ceramic cores. If adjust-ments are limited, these can be subsequently‘sealed’ by either polishing and/or re-glazing inthe dental laboratory. Adjustments are carriedout using a 12-fluted tungsten carbide finishingbur with copious irrigation, or aluminium oxideabrasive discs followed by silicone tips andrubber cups loaded with diamond polishingpaste. However, if extensive adjustments areenvisaged, a remake is a better option, savingclinical time and ensuring long-term viability ofthe restoration. The try-in stage consists of theextra – and intra-oral evaluation.

9Try-in procedures


CLINICAL PRACTICE

Extra-oral evaluation

Most all-ceramic systems require at least twopours of the dental biological impression. Thefirst plaster cast is left untrimmed, and, if neces-sary, mounted on to an articulator using afacebow and bite registrations. The second castis trimmed and the die sectioned for fabricatingthe definitive restoration (Figs. 9.2 & 9.3). An

Figure 9.1 Analysing faults at the try-in stage.

advantage of using addition silicone impressionmaterials is that multiple pours are possible, andthese may be difficult with reversible hydro-colloids and some polyethers. Although themaster cast can be duplicated by making impres-sions in the dental laboratory, this practiceshould be resisted. The greater the number oflaboratory stages, the greater the possibility ofintroducing error. Ideally, all pours should bemade from the original intra-oral impression,keeping laboratory stages to an absoluteminimum.

TRY-IN OF ALL-CERAMIC CROWNS ON MAXILLARY CENTRAL INCISORS

Shine through of discolored root through thin soft tissue.Crown margin needs to be moved further subgingivally,

cervical aspect requires a high-value porcelainplus definitive luting with a high-value resin cement

Open defective crown margin

The interdental contact pointis too apical requires a more coronal location

Swollen gingival margin due toloosening of temporaries,

leading to breakdown of marginal sealand plaque accumulation

Surface perikymata spacing oncrowns much wider

than that on natural teeth

The axial line angle of crown isdistally inclined, compared

to mesial inclinationof adjacent teeth

Crowns cemented with Provilink,patient informs that he can see hairline fracture lines.

All-ceramic crowns with a dense ceramic core, e.g. Procera or Empress, are necessary

to support veneering porcelain

Crowns devoid of incisal and interproximal translucencycompared to natural counterparts, resulting in

dense, opaque and non-vital appearance of crowns

Try-in procedures 187

Inspection of restoration on trimmed die

(1) Inspect intaglio surface for air blows or blebsthat impede correct seating on the die (Fig. 9.4). For all-ceramic units, passiveseating is essential to prevent initiation ofcrack formation. If a milled coping is usedas a substructure, it should have an idealcement spacing of less than 100µm. A tightfit is detrimental, causing stress within theceramic, while larger discrepancies create awider cement thickness layer, which mayyield under functional loads. In both sce-narios, a remake is advisable

(2) Correct die trimming is essential to delineatethe crown margins especially if CAD/CAM

technology with a scanner is utilised. Thefinish line should be marked with a finepencil (Fig. 9.5). In order to define the cir-cumferential finish line, an apical hollowbeyond the finish line is created by trimmingthe plaster cast 0.5mm horizontally and 1–2mm vertically (Fig. 9.6). The marginintegrity is severely compromised unless thisstage is meticulously performed. Havingconfirmed that the die is correctly trimmed,the crown is inspected under magnification,ensuring validity of the cervical margins.Since the die is trimmed by removing theplaster apical to the finish line, the emer-gence profile can only be assessed on theuntrimmed cast

(3) Ensure die spacer is sufficient to accommo-date cement lute (Fig. 9.7)

Figure 9.2 Untrimmed cast from the dental biologicalimpression.

Figure 9.3 Correctly trimmed die from the dental biologicalimpression for fabricating an all-ceramic crown.

Figure 9.4 Inspection of the intaglio surface for defects.

Figure 9.5 The finish line is marked using a fine pencil.


Inspection of restoration on untrimmed die

The remainder of the assessment is performed byplacing the restoration on to the untrimmed die:

(1) Verify that emergence profile is on a tangentto an area apical to the finish line in both thehorizontal and vertical planes (Fig. 9.8).Also, on a soft tissue model, ensure that thetransgingival contour is sufficient to supportthe FGM. Minor over-contouring can be

trimmed with appropriate rotary instru-ments, but deficiencies will require additionsor remake in the dental laboratory

(2) Ensure occlusion is correct in CR, CO andlateral and protrusive excursions (anteriorguidance), particularly if mounted on to anarticulator, using thin, coloured articulationpapers (40µm – Bausch, Koeln, Germany)and shim stock (8µm – Hanel, Langenau,Germany). Where difficulties are envisaged,a bisque try-in may be prudent to makeadjustments intra-orally, before returningthe restoration to the laboratory for polish-ing and glazing

(3) Aesthetics are better assessed intra-orally,but a cursory check of the following ishelpful: colour, characterisations, morphol-ogy, size (Figs. 9.9–9.11)

(4) Contacts. For posterior teeth, contactsshould be coronal to the interproximal col,preventing gingival entrapment and allowingease of oral hygiene procedures. They shouldbe tight and wide to prevent food impaction,without placing undue pressure on adjacentdentition. For anterior teeth, the contactsinfluence aesthetics with regard to the degreeof papilla fill, and are best assessed intra-orally.

Figure 9.8 Correct emergence profile of three all-ceramiccrowns.

Figure 9.6 Creating an apical hollow beyond the crownmargins delineates the finish line.

Figure 9.7 Die spacer for adequate cement space.

Try-in procedures 189

Intra-oral evaluation

(1) Remove therapeutic temporary restoration,provisional cement and clean abutment witha mixture of pumice and chlorhexidine paste

(2) Place definitive restoration on to abutment(3) Confirm marginal integrity using a silicone

paste, such as Fit Checker (GC)(4) Check emergence profile and the transgingi-

val contour, ensuring that the FGM is ade-quately supported by the cervical part of therestoration. Over-contoured restorationsblanch the gingivae, while under-contouringresults in unsupported and flaccid FGMs. If gross alterations are necessary, placecrown(s) on to abutment(s) and make a gin-gival biological impression, allowing theceramist to visualise the healthy, stableFGM, and adjust contour accordingly (Fig. 9.12) (Hint 9.1)

(5) Check occlusion with articulation paper, ina similar manner to extra-oral assessment.The best method of checking occlusion is inthe mouth, no articulator can substituteintra-oral verification. CR, CO and excur-sions are checked, with particular attentionto avoid introducing new defective contacts(see Chapter 2) (Hint 9.2)

(6) Finalise aesthetics, including colour (Hint9.3), morphology, size, surface texture, com-paring to adjacent and antagonist teeth (Fig. 9.13). Finally, check alignment of therestoration(s) in relation to lips and faciallandmarks, e.g. interpupillary line

(7) Phonetics – check ‘m’, ‘f’, ‘v’, ‘th’ and ‘s’sounds (see Chapter 2)

(8) Contacts. For posterior teeth, contactsshould be coronal to the interproximal col,preventing gingival entrapment and allowingease of oral hygiene procedures. They shouldbe tight and wide to prevent food impaction,without placing undue pressure on adjacentdentition. For anterior teeth, the contactsinfluence aesthetics with regard to thedegrees of papilla fill. Ensure that the contactpoint is 5mm or less from the bone crest,

Figure 9.9 Incisal translucency and characterisations of twoall-ceramic units.

Figure 9.10 Assessing surface texture and lustre.

Figure 9.11 Ultraviolet illumination checks fluorescence ofthe veneering porcelain.


mark position on the restoration and makeadjustments accordingly

(9) If alterations are necessary return restorationto dental laboratory; otherwise, proceed tocementation of the restoration (see Chapter10).

Hints and Tips

� Hint 9.1 – A gingival biological impres-sion is best achieved using a monophaseor soft addition silicone impressionmaterial

� Hint 9.2 – Using different colouredarticulation papers expedites occlusalassessment, e.g. red for CO, black forCR and blue for lateral and protrusiveexcursions. Shim stock is invaluable forensuring tight contralateral contacts forposterior restorations, while for anteriorsa light contact is desirable

� Hint 9.3 – To ‘optically connect’ therestoration with the underlying tooth forcolour assessment, fill the crown withchlorhexidine paste prior to seating

Figure 9.13 Incorrect colour: the crown on the right centralincisor is too grey and has a lower value compared with thenatural contralateral incisor.

Figure 9.12 Gingival biological impression with definitivecrowns to verify correct cervical contours and interproximalcontact points.

Theoretically, the purpose of a luting or cement-ing agent is uniting a dental restoration with theunderlying tooth, hermetically sealing it from theoral cavity. In reality, this ideal is often unfulfilledbecause of a variety of factors, including pre-paration design, the material from which therestoration is fabricated, choice of cement andclinical technique. Contemporary restorations,particularly all-ceramic prostheses, dictate achange in mind-set regarding cementation pro-tocols. Many older cements and techniques are considered redundant, and newer ceramicrestorations require technique-sensitive proce-dures for obtaining a lasting and durable bondto the abutment (implant or natural tooth).


The number of cements currently available isdaunting, leading to confusion regarding choicefor a specific restoration and clinical scenario. In order to make selection easier, this chapter discusses types of cements, their evolution andproperties, followed by guidelines for choosing

appropriate agents depending on the restoration.Finally, theory is applied to clinical protocols forcementing dental prostheses.

Types and properties of luting agents

The literature is unanimously emphatic that thetype of bond (chemical or micromechanical), itsdurability and quality between the restorationand abutment is dependent on choice of lutingagent and the technique employed for cementa-tion.1 The starting point is discussing the variousclasses of cements currently available. Below is alist of cements, in chronological order of devel-opment over the past decades, together with abrief summary of their advantages and disadvantages.

Zinc oxide eugenol (ZOE)

Advantages of ZOE include retrievability (pri-marily used for temporary restorations) and it is palliative to freshly cut and exposed vital

10Cementation and dentine bonding agents


dentine. There are many formulations, includingtransparent ones for improved aesthetics, andnon-eugenol varieties if using DBAs, whichprevent dentine contamination and formation ofthe hybrid layer.

Disadvantages of ZOE include high solubility,lack of adhesion (absence of chemical bond totooth substrate and fitting surface of prosthesis)and poor marginal integrity with increasedleakage. It is unsuitable for provisional cementa-tion of all-ceramic prostheses, due to the lack ofchemical adhesion to the underlying tooth sub-strate. Proprietary products include TempBond(Kerr, Orange, CA, USA).

Zinc phosphate (ZP)

Advantages of ZP include a proven track recordwith long-term clinical use, ease of use, it is expe-dient and technique forgiving. Disadvantagesinclude high solubility, lack of adhesion (absenceof chemical bond to tooth substrate and resto-ration interface), poor marginal integrity andincreased leakage. There are numerous propri-etary products.

Polycarboxylate (PC)

Advantages of PC include reduced pulpal irrita-tion and greater plastic deformation compared toZP and chemical adhesion to tooth substrate viafree carboxylic acid groups with calcium.2 Dis-advantages include a short working time and thetooth requires conditioning prior to cementation.There are numerous proprietary products.

Glass ionomer (GI)

Advantages of GI include fluoride release (cario-static), similar coefficient of thermal expansionto natural tooth structure and chemical adhesionto dentine and enamel. Disadvantages includepoor mechanical properties, e.g. low tensilestrength and fracture resistance, and susceptibil-ity to moisture during initial setting (therefore anarid environment is a prerequisite). A proprietary

product is Ketac-Cem (3M ESPE, Seefeld,Germany).

Resin-modified glass ionomer (RGI)

Advantages of RGI include improved tensile andcompressive strength compared to ZP and GIand resistance to water contamination duringinitial setting reaction compared to GI. Dis-advantages include that RGI is hydrophilic.Water adsorption and hygroscopic expansionlead to crack formation, cement deteriorationand intermediate leakage (between ZP and DR).A proprietary product is Fuji Plus (GC, Tokyo,Japan).

Dual-polymerisation resins (DR)

Advantages of DR are enhanced mechanical andaesthetic properties and chemical adhesion to thetooth with DBA and ceramics with appropriatepre-treatment of intaglio surface (depending on type of ceramic, e.g. silica, alumina or zirco-nia). Disadvantages are the protracted clinicalprotocols and therefore increased cost, and the technique-sensitive procedures required. Aproprietary product is Variolink II (Ivoclar-Vivadent, Schaan, Liechtenstein).

Self-adhesive, dual-polymerisationresins (SADR)

Advantages of SADR include ease of handling,no pre-treatment of tooth or fitting surface, high compressive strengths and diametral tensile strength,3 good aesthetic properties, che-mical adhesion to tooth (with DBA) and inta-glio surface by multifunctional monomer, 10-methacryloyloxydecyl dihydrogen phosphate(MDP) and high shear bond strength (SBS) with all restorative materials. A disadvantage isreduced fracture strength after artificial ageing.4

Proprietary products include Rely X Unicem(3M ESPE, Seefeld, Germany), Panavia F andPanavia F2.0 (Kuraray, Osaka, Japan).

Cementation and dentine bonding agents 193

Self adhesive, auto-polymerisationresins (SAAR)

Advantages of SAARs are that they are ideal formetal–ceramic and highly opaque all-ceramicrestorations (light-curing not necessary), andhave favourable mechanical and aesthetic pro-perties. They can be used for adhesion to:

� Tooth with DBA� Metal substructure of metal–ceramic crowns

intaglio surface by chemically bonding tometal oxides5 with the multifunctionalmonomer, MDP

� Alumina (Procera) pre-treated with air abra-sion and silane or ceramic primer

� Zirconia6 with air abrasion and ceramicprimer

A disadvantage is that some of the newer gen-erations of DBAs (sixth and seventh), whichcontain acidic components to etch, prime andseal dentine tubules simultaneously, form a resid-ual ‘acidic inhibition’ layer retarding the settingreaction of auto-curing luting agents. Whilstlight-cured polymerisation is immediate, withauto-curing the process is slower, allowing theacidic layer to interfere with complete setting at the cement–tooth interface, creating a fragilityzone.7 This non-homogenous zone has poormechanical and physical properties. There is no long-term clinical data about this. A pro-prietary product is Panavia 21 (Kuraray, Osaka,Japan).

Ceramic primers (CP)

� Porcelain Liner-M in combination withSuper-Bond C&B (Sun Medical, Shiga,Japan)

� Porcelain Bond Activator in conjunctionwith Clearfil SE Bond or Clearfil ProtectBond in combination with Panavia F,Panavia F 2.0, or Panavia 21 (Kuraray,Tokyo, Japan)

� Rely X Ceramic Primer in combination with Rely X Unicem (3M ESPE, Seefeld,Germany)

Efficacy of cementing agents

It is important to realise that most studies assess-ing properties of cementing agents, e.g. durabil-ity, are in vitro based, simulating mechanicalwear and ageing by cyclic loading and thermo-cycling, respectively. Whilst these thermo-mechanical fatigue models are invaluable forcomparing different products, they are not a true assessment of clinical durability, failing toaccount for negative factors, such as multi-directional non-axial occlusion forces, thermalstresses and saliva immersion. This is especiallysignificant with intra-oral stresses, since mostcement failures are attributed to tensile ratherthan compressive forces. In vivo studies are thegold standard, but are difficult to standardise,and are costly and time consuming. The key ele-ments for assessing suitability of various agentsare adhesion, mechanical properties, marginalintegrity (leakage) and retention.

Adhesion

Adhesion is categorised into true chemicalbonding and micromechanical interlocking,involving two interfaces (Fig. 10.1):

� Cement–tooth (enamel and/or dentine) interface

� Cement–restoration (metal and/or ceramic)interface

Figure 10.1 The cement–tooth and cement–restorationinterfaces.


In addition, the integrity of the intermediatecement layer between these two interfaces isessential for a successful union between toothand the restoration. Successful adhesion, ateither the cement–tooth or the cement–restora-tion interface, relies on formation of chemicalbonds as well as micromechanical interlocking.Whichever is achieved depends on the restorativematerial from which the prosthesis is fabricated,and the cement utilised. Ideally, a chemical bondis desirable at both interfaces as opposed tomicromechanical interlocking, but often thelatter compromise is apparent due to the restora-tive material and less than ideal clinical proto-cols. Table 10.1 summarises types of adhesionwith different cements at both the cement–toothand cement–restoration interfaces.

Modes of de-cementation are defined as adhe-sive or cohesive failures. Adhesive failures occurbetween the cement–tooth or cement–restorationinterfaces, while cohesive failures are encoun-tered within the intermediate cement layer or the underlying tooth substrate (Fig. 10.2). Themajority of failures are adhesive, usually betweenthe cement–tooth interfaces. This is the weakestlink of the crown/tooth complex, due to theweak dentine bond at the cement–dentine inter-face (especially the fragile hybrid layer).8 Con-versely, the bond strength at the cement–crowninterface (e.g. with ceramic etching/silane orceramic priming) exceeds that of the dentinebond with natural tooth.9

The bond strength (expressed as shear bondstrength – SBS) is dependent on not only the type

Table 10.1 Types of adhesion with different cements.

Interface Micro-mechanical interlocking Chemical bonding

Cement–tooth ZOE, ZP, DRi PC, GI, RGI, DRiii, SADRiii, SAARiii

Cement–restoration ZOE, ZP, PC, GI, RGI, DRii DRiv, SADRiv, SAARiv

i without DBA.ii without pre-treatment of intaglio surface.iii with DBA. The bond between dentine and resin cements is via dentine adhesion using a DBA. This is not a true chemicalbond, but micromechanical in nature, involving formation of the hybrid and adhesive layers, which ‘connect’ to resin cements.iv with appropriate pre-treatment of intaglio surface depending on restorative material.

of cement but also on tooth preparation design,including retention and resistance form, margingeometry (finish line) and degree of taper (con-vergence angle). In addition, the SBS varies initially and following ageing. The non-resincements, such as ZOE, ZP, GI and RGI, exhibitdeterioration of SBS after exposure to water andthermal cycling, while the resin cements, such asDR, SADR, may exhibit an increase in SBS dueto postpolymerisation, which enhances mechan-ical resilience. However, protracted ageing of theresins has revealed complete adhesive failuremodes at the cement–ceramic interface followingthermal cycling.

Another point worth noting is that with RGIsfailure can occur at both cement–dentine andcement–crown interfaces, while resin cementswith an adhesive cementation technique onlyhave deterioration at the cement–dentine inter-face. Finally, cements containing an adhesivephosphate monomer (MDP), used in conjunctionwith air abrasion for alumina and zirconiaceramics, exhibit increased initial and long-termbond strengths.

Occlusal stresses

The mean human masticatory force is 40N, butin the posterior regions, the forces can vary from200–540N, depending on facial anatomy andage.10 All-ceramic restorations inherently sufferfrom brittleness and are susceptible to tensile andtorsional stresses.11 In order for a restoration to


survive, it is desirable that it matches or exceedsthese forces. Many currently available all-ceramic systems can withstand the maximummasticatory forces encountered on posteriorteeth, with fracture resistance comparable tonatural teeth.12 The fracture strength of aceramic depends on inherent flexural strengthand MOE, and the skill of the ceramist duringfabrication and manipulation of the material.For example, autoglazing may be inadequate for

sealing microsurface irregularities, whereas over-glazing may close surface defects exposed to theoral environment and minimise potentially cata-strophic fractures.

Marginal integrity and leakage

Marginal discrepancies and leakage at thecement–tooth or cement–restoration interfacesare susceptible to periodontal disease, secondarycaries, staining (poor aesthetics), post-operativesensitivity, crown dislodgement and ultimatefailure of the restoration. Therefore, the sealingability of a luting agent is crucial for longevityand durability. The first aspect to consider iscorrect seating on to the abutment tooth. Crownelevation due to improper location or seatingintroduces vast discrepancies, and compromisesaesthetics due to staining of the cement line.Nevertheless, as one study points out, the thick-ness of the cement line is not directly related tothe extent of microleakage.13

Secondly, light polymerisation increases SBS ofdual-polymerisation cements, allowing completesetting with superior physical and mechanicalproperties, especially for subgingival margins.However, photoactivation causes rapid curingcreating higher stresses at the bonded interfaces,increasing the risk of microleakage compared toauto-cured cements, which have time for viscousflow.14

The next factor is margin opening due toageing. In vitro studies simulate ageing usingthermal and mechanical stresses by thermocy-cling and cyclic loading, respectively. The resultof ageing manifests as marginal integrity deteri-oration, and is influenced by the type of luting agent. This is particularly evident withmetal–ceramic crowns, where ageing increasesleakage.15 However, a recent study reveals thatall-ceramic crowns cemented with resin cementshave little differences in marginal discrepancyafter simultaneous thermocycling and cyclicloading. This is explained by the fact that the ver-tical, in vitro cyclic loading causes compressivestresses, closing margins. However, during mas-tication, both vertical and horizontal (tensile)stresses are encountered, which are not repro-

Figure 10.2 Adhesive failure of porcelain laminate veneer.


duced in the in vitro set-up. The same study alsoemphasises intermediate and severe leakage withRGI and ZP cements, respectively.16

Retention

Retention is the ability of a restoration to resistdisplacement in the opposing direction to inser-tion. It is primarily dependent on the geometryof the preparation, including the height, width,surface area and degree of taper. The item thathas attracted most attention is the degree oftaper.17 It is important to clarify terminologyregarding the angulations and configurations ofa tooth preparation. Taper refers to the angle ofa single wall, usually mesial or distal, while theconvergence angle refers to the combination ofthe tapers for a given preparation. For example, the ideally quoted convergence angle of 12° isderived by the addition of the two axial walls (6°mesial and 6° distal tapers). Decreasing the taperincreases retention and surface area, but exces-sively parallel (small tapers) preparations causeincorrect seating.

Another factor determining the degree ofretention is the choice of cement. ConventionalZP cements are luting agents, which rely oninterlocking irregularities of the intaglio andtooth surfaces for retention, while GI and resincements create chemical bonds with artificialprostheses. With ideal tapers of 6–12°, the choiceof cement becomes irrelevant to retention of thecrown. Hence, retention is not compromisedwhen the taper increases from 6° to 12°. Butbecause conventional cements do not offer adhe-sion, cement dissolution may predispose tomicroleakage over time. In clinical practice, theaverage taper of a tooth preparation ranges from14–20°, making the choice of cement a crucialfactor for retention.18 For example, taperincreases from 6° to 24° decrease retention of allcements; ZP by 42%, GI by 38% and resincements by 20%. In addition, GI and ZP cementsoffer similar retention (3.6MPa), half the valuescompared to resin cements (6.5MPa), irrespec-tive of taper angle. Furthermore, for a 24° taper,resin cements offer retention comparable toluting with ZP with a 6° taper.

The clinical significances are as follows:

� Resin cements offer superior retention� ZP and GI cements offer similar retention

values with tapers of 6–12°, and the choiceof cement is irrelevant (with the disadvan-tages of absence of adhesion, weakermechanical properties, microleakage, mar-ginal staining, and post-operative sensitivity)

� When the taper increases to 24°, resincements offer better retention than both ZPand GI luting agents.19 Using resin lutingagents for less than ideal tooth preparationsoffers superior marginal adaptation,20 andhigher fracture resistance,21 especially if therestoration is susceptible to high occlusalloads22

Table 10.2 suggests the ideal choice of cementfor different types of restorations.

Table 10.2 Choice of cements for different restorations.

Material Ideal cement choice

Acrylic or composite ZOE, ZP(temporary crown)

High-gold alloy SAARSemi- or non-precious alloy SAARSilica ceramicsi DR, SADR, SAARAlumina ceramicsii SAARZirconia ceramicsiii SAARImplant-supported prostheses ZOEiv

i Silica ceramics – e.g. feldspathic, leucite reinforced glass ceramic (Empress 1 – Ivoclar-Vivadent, Liechtenstein),lithium disilicate glass ceramic (Empress 2 – Ivoclar-Vivadent,Liechtenstein).ii Alumina ceramics – e.g. densely sintered pure aluminumoxide ceramic (Procera, Nobel Biocare, Sweden), glass infil-trated alumina (In-Ceram, Vita, Germany).iii Zirconia ceramics – e.g. Cercon (Dentsply, Germany), Lava (3M-ESPE, Germany), Procera Zircon (Nobel Biocare,Sweden).iv Alternatively, use acrylic/urethane polymer proprietaryimplant cement (ImProv, Nobel Biocare, Sweden).


Pre-treatment of abutment

Two surfaces require pre-treatment, firstly thecut dentine and enamel following tooth prepara-tion, and secondly the intaglio or fitting surfaceof the restoration. Traditionally, before theadvent of DBAs, the prepared tooth surface wasleft untreated, an impression made, temporaryfabricated and the definitive restoration lutedwith a conventional cement. The introduction ofDBAs, and their development over the last half-century, have revolutionised cementation pro-tocols. Today, DBAs are pivotal, not only fordirect composite and amalgam restorations, butfor nearly all indirectly fabricated laboratory prostheses.

Two modes for pre-treatment of the preparedtooth abutment using DBAs are possible, eitherat cementation of the definitive prosthesis, orimmediately after tooth preparation.23 Numer-ous studies have concluded that application of aDBA after preparation produces a wider hybridlayer with longer and abundant resin tags. Thesetags have a lower MOE than the overlying resincement with inherent elastic buffering capacity,absorbing shocks and stresses placed on the arti-ficial restoration.24 Furthermore, the mircotensilebond strength is greater, with reduced micro-leakage and post-operative sensitivity.

Dentine bonding agents

Introduction and development of DBAs have rev-olutionised many clinical procedures, includingcementation. Their use is commonplace in contemporary dental practices for numerousapplications and therapies. In addition, lutingall-ceramic restorations using DBA and resincements improves longevity.25

Buonocore conceived bonding to enamel overhalf a century ago with the introduction of acidetching.26 Although composite fillings of theperiod were relatively inferior compared to con-temporary analogues, the technique for inter-locking a resin to enamel prisms is still applicabletoday, as it was in 1955. Adhesion to dentine, onthe other hand, has proved far more elusive. The

reason is that bonding to an inorganic substance,such as enamel, is far easier than the organic andinorganic complex prevalent in dentine. Whilethe theoretical mechanism of dentine bonding is understood, the practical achievement is stillunattainable. The following discussion highlightscurrent thinking and evolution of DBAs.

Dentine bonding mechanism

Traversing from enamel to the dental pulp, thereis an increase in both the organic phase andwater content (Figs. 10.3 & 10.4). The inorganicenamel is hydrophobic, while the dentine andpulp are hydrophilic. A viable bond is only pos-sible in a hydrophobic environment, hence theease of bonding to enamel. For dentine, the envi-

Figure 10.3 Sectioned natural tooth (transmitted light)showing enamel and dentine strata.

Figure 10.4 Sectioned natural tooth (ultraviolet light)showing enamel and dentine strata.


ronment must be transiently converted into a hydrophobic state conducive for successfulbonding, which is the basic aim of all DBAs.

Technological and material advances haveimproved the efficiency of dentine bonding, forexample, the total etch technique and use ofhydrophilic primers in bonding agents.27,28 Den-tine bonding, or adhesion, is micro-mechanicalin nature, succinctly described as follows. Thefirst step is removing the smear layer (Fig. 10.5)by conditioning to demineralise the inorganicphase and expose the dentine tubules (Fig. 10.6)and collagen fibres (Fig. 10.7), constituents of theorganic phase of dentine. Next, the surface isprimed by monomers (to create a hydrophobic

environment), which facilitates the last stage ofresin impregnation and penetration to encapsu-late and stabilise the collagen network.29 Theresultant entity is a resin-reinforced dentine,which has differing nomenclature, dependinghow the latter is envisaged: hybrid layer (unionof resin and collagen fibres)30, interdiffusion zone(permeation of dentine by resin)31 or RIDL(resin-infiltrated dentine layer).32 The termino-logy is irrelevant, but the significance is that amicromechanical connection is made betweendentine and the resin that functions as a viablebond (Fig. 10.8).

Figure 10.5 Smear layer following tooth preparation.

Figure 10.6 Exposed dentine tubules after removal of thesmear layer.

Figure 10.7 Exposed collagen fibres after removal of thesmear layer.

Figure 10.8 Formation of the hybrid layer with resin tagswithin the dentine tubules.


The appearance, size, composition and qualityof this hybrid layer have attracted much atten-tion among researchers and clinicians. Thedimension of this layer has wide variance,ranging from 2–10µm, but even thin layers havebeen shown to produce very high immediatebond strengths.33 It transpires that the thicknessand morphology of the hybrid layer seems lessimportant than its consistency and integrity (lackof gaps, porosity and voids), which are para-mount for achieving efficacious and durabledentine sealing and bonding.34

Generations

Achieving efficacious dentine bonding relies onan agent or agents to condition, prime and sealtubules and stabilise the collagen fibres, previ-ously supported by the inorganic phase. DBAsare categorised into three types:

� Multi-component (MC) (Fig. 10.9)� Single component (SC) (Fig. 10.10)� Self-etching (SE) (Fig. 10.11)

The MCs require application of individualcomponents for each bonding stage. Initially, theetchant, usually 37% phosphoric acid, is applied,rinsed and dried to remove the smear layer. Arecent study concludes that a combination ofphosphoric and hydrofluoric acid results in supe-

rior marginal seal at the cement–tooth inter-face.35 The next stage is application of a primerthat subsequently evaporates, and finally an ad-hesive resin is introduced to seal the tubules andform the hybrid layer. These multi-componentsystems show diversity in their presentation andmake up, forming the first to fourth generationsof dentine adhesives.

The SC systems combine the primer and adhe-sive into one component, but still require aninitial total etching step and are termed fifth gen-eration, e.g. Scotchbond 1, Syntac Single andSyntac Sprint. Finally, the SE agents obviate theneed for etching by incorporating pyrophosphate

Figure 10.9 Multi-component (MC) bonding agents requireapplication of individual chemicals to achieve the desiredresult. Firstly the etchant (green), secondly the primer (yellow)and finally the adhesive (red).

Figure 10.10 Single-component (SC) bonding agents requireapplication of two chemicals to achieve the desired result.Firstly the etchant (green) and secondly the combined primerand adhesive (red).

Figure 10.11 The self-etching (SE) bonding agents requireapplication of only one chemical to achieve conditioning,priming and sealing/adhesion.


initiators, e.g. Etch & Prime 3 (Dentsply,Germany), and iBond (Heraeus Kulzer,Germany) (Fig. 10.12), forming the sixth andseventh generations, respectively. A recentlyintroduced SE, seventh generation dental adhe-sive is iBond GI (Heraeus Kulzer, Hanau,Germany). The ‘i’ is an abbreviation for ‘intelli-gent’ or ‘innovative’, as the need for mixing com-ponents before application has been eliminated,while ‘GI’ signifies inclusion of the Gluma desen-sitiser. The constituents of iBond include all threechemicals necessary for dentine bonding, i.e.etching, priming and adhesive resin. The solventis a mixture of acetone (promoting evaporation)and water (facilitating hydration of the collagenfibres and the self-etching mechanism). Its prop-erties boast a SBS to both dentine and enamel inexcess of 20MPa, and a marginal gap of almostzero.36

The clinical protocols are crucial for achievingan effective and successful bond, and the entireprocedure is extremely technique sensitive. It isimperative that the components infiltrate, minglewith, and finally encapsulate the remaining collagen matrix. Failure at any of these stagesresults in a compromise, leading to deteriorationby water, infestation by bacteria and a break-down of the collagen fibres, no longer supportedby the hydroxyapatite crystals. Therefore, theadvantages of reducing the number of compo-nents are obvious. Fewer clinical steps ultimatelyreduce the scope for error. The SE agents are

essentially ‘automatic’ DBAs, expediting dentinebonding. The clinician is no longer burdenedwith precise timings for application of etchant,primer and resin to prevent collapse and pene-tration of the collagen matrix, which is necessarywhen using MC systems.

Solvents

Solvents are significant constituents of primers,precursors of the adhesive resin. The function ofsolvents is to promote wetting of dentine, and toact as water chasers and monomer carriers forinteraction with collagen fibres. The solvents cur-rently used are hydrophilic, categorised as eitherorganic (acetone and ethanol) or inorganic(water) (Figs. 10.13–10.15).

Acetone is frequently used as a solvent; it has a boiling point of 56.5°C, efficiently re-moves water from the substrate, facilitates resinpenetrations and yields a superior bond withdentine.37 However, it fails in preventing collapseof the collagen matrix if applied to dehydratedor arid dentine. Furthermore, acetone-basedagents are more technique sensitive, requiringstrict adherence to manufacturer’s guidelines foruse.

Water has a boiling point of 100ºC and istherefore less volatile than acetone. This resultsin water retention, obscuring the collagenmatrix, impeding infiltration of HEMA (adhesiveresin) molecules, and therefore reducing the

Figure 10.12 An example of a SE DBA is iBond (HeraeusKulzer). Figure 10.13 Organic solvent: acetone.


quality of the hybrid layer. However, water doeshave the advantage of re-erecting collapsed col-lagen fibres favouring monomer penetration,38

and eliminating the need for moist dentine.Ethanol has a boiling point of 78.5ºC, inter-

mediate between acetone and water, and ispresent in many fifth generation bondingsystems. Ethanol-based agents are less techniquesensitive than acetone and more efficient atremoving water than water-based systems. Manyformulations on the market exploit the benefitsof each solvent by using a combination to gainoptimum results, e.g. in a mixture of acetone andwater, the water stabilises acetone evaporationand promotes wetting of dentine, while theacetone encourages evaporation of water, facili-tating monomer and resin penetration.39

Efficacy

Bonding efficacy is usually assessed by twoparameters, the marginal gap at thecement–tooth interface and the SBS. As a com-parison, mean SBSs to enamel are in the range of23–25MPa. Assessing dentine SBS is erratic,often dependent on the in vitro experimentalmodel and measurement criteria. The SBS fordentine ranges from as little as 3.5MPa to aslarge as 25MPa, equalling that of enamel.40

These figures should be viewed with cautionsince they do not represent a clinical environ-ment; further research and in vivo trials willeventually reveal credible values.

The second factor used for assessing bondingefficacy is the marginal opening (MO) at thecement–tooth interface. Again, no definitivevalues are ascribed, ranging from 0–10µm,41 butminimising this gap is essential for success andlongevity. Large MOs result in caries, pulpalpathologies, discolouration and, ultimately, dete-rioration of the resin luting agent. However, mar-ginal integrity is not solely influenced by thebonding agent, but also by clinical procedures,such as preparation design, adequate isolation(retraction cord or rubber dam), applicationtechniques and modes of light polymerisation(Figs. 10.16–10.18).

Numerous studies have reported that thenewer SC and SE agents, even with thin hybrid

Figure 10.14 Inorganic solvent: water.

Figure 10.15 Organic solvent: ethanol.

Figure 10.16 DBA application protocol: three coats of a SE bonding agent are successively applied to all cavity surfaces.


layers (0.5µm), show similar bonding capabili-ties to those of traditional MC systems.42,43,44,45

Pre-treatment of intaglio surface

After pre-treatment of the abutment tooth, thenext step before cementation is pre-treatment ofthe intaglio of the restoration. Pre-treatment ofthe adherent surface varies according to therestorative material of the prosthesis, and can becategorised into mechanical and chemical.

The aim of any mechanical roughening isenhancing adhesion by micro-mechanical reten-

tion. Prostheses fabricated by CAD/CAM andmilling processes have inherent surface rough-ness due to the manufacturing process (Fig.10.19). This is analogous to etching silica-basedceramics with hydrofluoric acid to increasemicro-mechanical interlocking. Surface roughen-ing with diamond burs and aluminium oxidediscs is useful for metallic surfaces, but excess or indiscriminate roughening of ceramics initi-ates crack formation causing weakening or frac-tures. Micro-etching surface roughening with air abrasion using aluminum oxide particles(50–100µm) has a similar effect to rotary instru-ments for fragile ceramics, initiating micro-fractures and therefore compromising physicalresilience. This is particularly significant withweaker feldspathic or leucite-reinforced glassceramics, but less important for high-strengthceramics such as alumina or zirconia. Neverthe-less, luting agents have proven successful forsealing these micro-flaws while significantlyenhancing adhesion.46

Chemical pre-treatment achieves either micro-mechanical interlocking, or true chemicalbonding. For silica-based ceramics, phosphoricacid (37%) only decontaminates with no effecton intaglio surface topography, but hydrofluoricacid (5–9.5%) for 5 minutes decontaminates andetches porcelain, creating pronounced surfacerelief and tunnel-like undercuts, and, in con-

Figure 10.17 DBA application protocol: air is used to evap-orate the acetone solvent from the bonding agent.

Figure 10.18 DBA application protocol: light curing for 30seconds completes the bonding process.

Figure 10.19 The intaglio surfaces of Procera copings haveinherent surface roughness.


junction with a silane-coupling agent, formschemical bonds at the cement–restoration inter-face. The SBS (approx. 22MPa), irrespective ofthe resin luting agent and DBA, is highest whenthe intaglio surface is treated with a combinationof hydrofluoric acid and silane.47

Using hydrofluoric acid for high-strengthceramics, such as alumina and zirconia, has noeffect on surface roughening for micro-mechani-cal interlocking. The application of silane forhigh-strength ceramics is controversial. Theoret-ically, since the pure alumina or zirconia lacksilica, the formations of chemical silane–silicabonds are absent. However, some studies advo-cate use of silane as it increases wettability.48 Onestudy has reported the highest initial SBS (21MPa) and after artificial ageing (16MPa), usingair particle abrasion, silane and an SAARcement.49

Ceramic primers (CP) and self-adhesivecements are another way for achieving chemicalbonding at the cement–restoration interface. Thenewer multi-component CP can be used as a substitute for hydrofluoric acid and silane pre-treatment for silica-based ceramics, expeditingprocedures without compromising bond strengthor integrity.50 Using a CP in conjunction withSADR and SAAR cements is a pre-requisite fora chemical bond with alumina and zirconiaceramics. Some studies advocate airborne alu-minum oxide (Al2O3) particle abrasion51 and asilane coupling agent in combination with aMDP-containing resin luting agent (Clearfil SEBond and Clearfil Porcelain Bond Activator,Kuraray Tokyo, Japan) to increase the SBS, evenafter ageing of zirconia-based ceramics.52 It isimportant to note that the chemical compositionand manufacturing of specific zirconia substruc-tures with different intaglio morphologies isunique for each commercial product. Hence,conclusions derived from a single study may notbe applicable to every zirconia prosthesis. Inaddition, the significant factor for yielding high-bond strengths to zirconia is application of aMDP-containing bonding/silane coupling agent,irrespective of the resin cement. The latter is con-firmed when using a bonding/silane couplingagent without a MDP, which results in weakerbonds to both alumina and zirconia ceramics.53

Table 10.3 summarises pre-treatment of differentintaglio surfaces for optimal adhesion.

CLINICAL PRACTICE

Cementation should not be considered the finalstage for the provision of artificial dental pros-theses. In fact, it is the penultimate stage, pre-ceding periodic maintenance and review toensure survival and compatibility of the prosthe-sis with the surrounding hard and soft tissues.The following is a clinical sequence for cemen-tation:

(1) Remove therapeutic temporary restoration(Fig. 10.21)

(2) Isolate tooth abutment with retraction cord(Fig. 10.22) (Hint 10.1). Isolation of thetooth before bonding has recently becomea point of contention. Some studies havestated that presence of ambient humidity54

and contamination by saliva has no adverseeffect on bond strength.55,56 However, thesenew concepts require further validation,and, in the author’s opinion, it is probablyprudent to isolate for a reliable dentinebond and inadvertent spillage on to the softtissues, avoiding transient and reversibleacidic burns. The cord functions as a

Figure 10.20 Alloy primer application to a cast metal core.


barrier between the epithelial attachmentand the luting agent, ensuring integrity ofthe biologic width, as well as allowing clear visualisation of the tooth margins andmaintaining a moisture- and contaminant-free environment (Hint 10.2)

(3) Rinse abutment with water to remove rem-nants of provisional cement

(4) Clean abutment with pumice mixed with0.2% chlorhexidine paste, rinse and dry(not desiccate) with a gentle stream ofwarm air (Fig. 10.23)

(5) Place definitive prostheses on to abutmentto verify fit, correct seating and occlusion(Hints 10.3 and 10.4)

(6) Pre-treatment of the intaglio surface ofprosthesis. The type of pre-treatment willdepend on the restorative material of theprosthesis (see Table 10.3) (Hint 10.5)

(7) Pre-treatment of abutment. Use DBA of choice, according to manufacturer’sinstructions. If using a SE all-in-one DBA(Hint 10.5), etch uncut enamel and scleroticdentine with 37% phosphoric acid for 20seconds, rinse and dry (not desiccate), applySE agent. Alternately, if using a fifth gener-ation DBA, etch entire abutment with 37%phosphoric acid for 20 seconds, rinse anddry (not desiccate) before successivelyapplying primer and adhesive (Hint 10.7).The highest SBS (15–20MPa) to dentine isachieved using light-cured or chemical-cured DBAs; dual-cured DBAs achieve SBSof 8–12MPa. This is because the dual-cured DBAs have additives to their solvents,which dilute the desired mixture of primerand adhesive necessary for forming a viablehybrid layer57 (Fig. 10.24) (Hint 10.8)

(8) Choose appropriate cement from Table10.2 for specific restoration, and mixaccording to manufacturer’s instructions

(9) Load cement into the prosthesis, and seatpassively on to abutment (Fig. 10.25)

(10) Once correctly seated, gently ease retrac-tion cord from gingival sulcus together withextruded excess cement (Fig. 10.26) (Hint10.9)

(11) Use dental floss, tape or Super Floss (Oral-B) to mop interproximal excess cement

(12) Apply oxygen-blocking gel (Oxyguard II,Kuraray, Osaka, Japan) around margins tominimise oxygen inhibition layer

(13) Apply gentle pressure to the prosthesis untilcement is completely set, or polymerisewith a curing light if using dual-curedcements (Fig. 10.27)

(14) Remove oxygen-blocking gel with cottonwool swabs

(15) Cut set excess cement around margins witha #12 scalpel blade (Fig. 10.28)

(16) Irrigate gingival sulcus with a 0.2%chlorhexidine solution to remove setcement remnants and promote gingivalhealth (Fig. 10.29).

Figure 10.21 Cementation protocol: remove temporaryrestoration.

Figure 10.22 Cementation protocol: isolate tooth withretraction cord (right central incisor).


Table 10.3 Intaglio surface pre-treatment.

Material/ Acrylic or High- Semi- or Silica Alumina Zirconia Implant-pre-treatment composite gold non- ceramicsi ceramicsii ceramicsiii supported

(temporary alloy precious prosthesescrown) alloy

Rotary N Y Y N N N Ninstruments

Al2O3 air Yiv Yiv Yiv N Yiv Yiv Nabrasion

Alcohol Y N N N N N Nv

Tin plating N N Yvi N N N NPhosphoric acid Y N N N N N N

(37%)Hydrofluoric acid N N N Y N N N

(5–9.5%)Silane N N N Yvii Yvii Yvii NCeramic primer N N N Yviii Y Y N

Y – Yes.N – No.i Silica-ceramics – e.g. feldspathic, leucite reinforced glass ceramic (Empress 1, Ivoclar-Vivadent, Liechtenstein), lithium disili-cate glass ceramic (Empress 2, Ivoclar-Vivadent, Liechtenstein).ii Alumina ceramics – e.g. densely sintered pure aluminum oxide ceramic (Procera, Nobel Biocare, Sweden), glass infiltratedalumina (In-Ceram, Vita, Germany).iii Zirconia ceramics – e.g. Cercon (Dentsply, Germany), Lava (3M-ESPE, Germany), Procera Zircon (Nobel Biocare, Sweden).iv Following air abrasion, clean restoration in an ultra-sonic bath to remove all traces of the aluminum oxide powder.v Traces of alcohol after cleaning the intaglio surface of the prosthesis may cause necrosis of the epithelial cells of the trans-mucosal attachment, or cuff, around an implant abutment.vi Pre-treatment of the intaglio surface with an alloy primer (e.g. Alloy Primer, Kuraray, Osaka, Japan) negates tin plating (Fig.10.20).vii Silane has a relatively short self-life, and is most effective when warm. Ensure silane is not used beyond expiry date, and thatthe intaglio surface is heated (e.g. with a hair drier) before application of the silane.viii As a substitute for hydrofluoric acid and silane.

Figure 10.23 Cementation protocol: clean abutment withpumice and chlorhexidine paste. Figure 10.24 Cementation protocol: apply DBA.


Figure 10.25 Cementation protocol: seat cement-loadedcrown on to abutment.

Figure 10.26 Cementation protocol: remove retractioncord.

Figure 10.27 Cementation protocol: light polymerisation ifusing dual- or light-cured luting agents.

Figure 10.28 Cementation protocol: remove set cementwith a #12 scalpel blade.

Figure 10.29 Cementation protocol: irrigate with chlorhex-idine solution.


� Hint 10.1 – Use dry, non-impregnatedretraction cord to absorb crevicular fluid

� Hint 10.2 – Avoid using retraction cordaround implant abutments, because thetrauma from cord placement damages theepithelial attachment of the transmucosalcuff. This results in undesirable gingivalrecession, and possible apical migration ofthe biologic width with ensuing bone lossaround the implant fixture. The latter isparticularly relevant with a thin, scallopedperiodontal biotype

� Hint 10.3 – If crown margins are subgin-gival or indiscernible, use a silicone try-inpaste, such as Fit Checker (GC, Tokyo,Japan), to confirm fit and seating

� Hint 10.4 – The occlusion should havebeen finalised with the therapeutic tempo-rary restoration(s) and at the try-in stage.However, minor adjustments can be performed with appropriate rotary in-struments with copious irrigations andmeticulously polished to close surfaceirregularities (micro-fractures) by usingfine diamond burs (less than 20µm grit),tungsten carbide finishing burs (20 to 30fluted), silicone tips and diamond polish-ing pastes

� Hint 10.5 – Pre-treatment of the intagliosurface can be delegated to the dentalassistant, and performed either before or concurrently with pre-treatment of theabutment. This ensures that the pre-treatedtooth after DBA application is not left unat-tended, avoiding detrimental contamina-tion with oral fluids

� Hint 10.6 – It is recommended to use cor-responding DBA from the same manufac-turer as the luting agent, ensuringchemical compatibility of the DBA withthe luting agent

� Hint 10.7 – The following points should befollowed prior to using a DBA. Many sol-vents in DBAs are extremely volatile, andsealing the bottle after dispensing ismandatory, avoiding unwanted evapora-tion. Next, the solution should be refriger-ated (4–10°C), ensuring consistency of thecomponents, and brought to room tem-perature 1 hour before use. In addition,stagnant containers have an undesirablephase separation of the solvent and activeingredients, and shaking the bottle beforeuse is essential to re-mix these compo-nents, ensuring that the adhesive functionsas intended. Finally, a uni-dose rather thanbottle dispensers are preferred, ensuringsterility, ease of use and chemical consistency

� Hint 10.8 – Most failures with DBA occurdue to insufficient evaporation of thesolvent. After application and dwell time,dry DBA with a gentle stream of air untilno liquid movement is detected and thesurface has a glossy appearance; depend-ing on the surface area of the abutment,this usually takes 10–15 seconds

� Hint 10.9 – Avoid using auto-curedcements with SE DBAs, since the latterform an ‘acidic inhibition’ layer, whichinterferes with complete setting of auto-cured cements

Hints and tips


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Index

0.618 (golden proportion), 46, 47#12 scalpel blade, 204, 206

AAberrations

chromatic, 82, 86spherical, 82, 86

Abrasion, 110Absolute threshold, 87Abutment pre-treatment, 197, 204–207Accommodation, 81, 86Acetone, 200Achromatic vision, 82Acidic burns, 203Acidic inhibition layer, 121, 193, 207Adaptive response, 35Adhesion, 193–4Adhesive

failure, 70, 194layer, 152, 194resin, 151, 199, 200

Adhesive phosphate monomer (MDP), 192, 193,194, 203

Aesthetic appraisal, 38, 39, 51–2Ageing, 42, 193Air abrasion, 202, 203Alcohol necrosis, 205All-ceramic, 55Allergy, 58Alloy primer, 203, 205

Altered passive eruption, 26Alumina, densely sintered, 58Alveolar bone crest (ABC), 24, 29, 127, 129, 136,

137, 175, 189Alveolar housing, 117Amalgam

bonding, 100cores, 101

Anterior guidance, 33–4Apical seal, 117Apicectomy, 146APT (assessment, planning and treatment), 1, 135,

140Articulation paper, 188, 189Articulator, see semi-adjustable articulatorAssessment, 1, 12Astringent, see haemostatic agentAtraumatic, 176–7Attrition, 110Automated mixing, 168Axial inclination, 46, 148, 186

BBalance, 43Beautiful proportion, 46Biocompatibility, 55, 58, 104, 105, 151Biofilm, see plaqueBioform, see periodontal, bioformBiologic width, 24, 25–6, 121, 127, 168, 174, 175,

204

212 Index

Biological impressionsdefinition, 165dental, 177–9

multiple pours, 169, 170, 179, 186disinfecting, 170, 179, 181, 182gingival, 179–81, 189, 190one-stage, 167passive, 168, 178, 181primary determinant, 172–7secondary determinants, 166–72two-stage, 167

Biomechanics, 98, 113Biotype, see periodontal, biotypeBite force, 60, 66Black triangles, 127, 128, 130, 148Bleaching, 110Bond strength, 115, 192, 194, 195, 200, 201, 203,

204Bone architecture, 48Boxes, 99, 102, 102, 121Brain

bottom-up processing, 84corpus callosum, 84top-down processing, 84

Brannstrom’s hydrodynamic theory, 151Brightness constancy, 87Brittle, 58, 157, 194Build-up, 101, 102, 120, 141Burs, 130–42

CCAD/CAM, 63, 65, 66, 70, 131, 141, 187,

202Canine disclusion, 33Canine guidance, 32, 33Cariostatic, 101, 110, 192Cement–enamel junction (CEJ), 24, 137Cements, 100, 109

dual-polymerisation resins (DR), 131, 192glass ionomer (GI), 192resin-modified glass ionomer (RGI), 192selecting, 196self-adhesive auto-polymerisation resins (SAAR),

193self-adhesive dual-polymerisation resins (SADR),

192zinc oxide eugenol (ZOE), 161, 191–2zinc phosphate (ZP), 131, 192

Ceramicsalumina, 70, 111, 203bi-layer, 58, 70, 132choosing, 73fabrication, 61

high-strength, 67ingots, 108mechanical properties, 61monobloc, 108posts, 104silica, 58, 61, 203uni-layer, 58, 132, 185zirconia, 68–9, 72, 73, 111, 196, 203, 205

Cerebral cortex, 84Cerebral hemispheres, 84Cerestore, 70Chamfer margin, 131Chemical bond, 203, 194Chlorhexidine, 161, 189, 190, 204, 205Chroma, 79, 80, 88, 91, 93, 96Chromatic assessment period (CAP), 87, 96Chromatic

adaptation, 87, 96graffiti, 83map, 94, 95, 96stability, 58, 155vision, 82

CIE Lab, 81, 91Clinical trials, 7, 69, 70Coefficient of thermal expansion, 58, 192Cohesive failure, 70, 194Cohesive forces, 39, 43Col, 188Collagen fibres/matrix, 198Colorimeter, 80, 94Colour

acceptable, 87blindness, 83, 86conscious perception, 78constancy, 87context, 86co-ordinates, 80, 85, 92difference, 87dimesions, 79experience, 78match, 88, 189multi-stage theory, 83objective analysis, 93–4, 96paraconscious perception, 78perceptible, 87perception, 77prescription, 92rendition, 79, 85sensation, 77single-stage theory, 83spaces, 80stimulation, 77, 78subconscious perception, 78

Index 213

subjective analysis, 94–6temperature, 78, 85therories, 83vision, 77

Commissural line, 43Complementary colour, 83, 110Compliance, 174Compressive strength, 132, 192, 193Cones, 82Connective tissue attachment (CTA), 24Connectors, 69, 70, 72, 73Contact points, 181, 186, 188, 189Convergence angle, 131, 132, 146, 194, 196Coping, 67Core

materials, 100–102types, 113–14

Coronal dentine, 118Corrosion, 55, 58, 103, 104, 110Cosmetic dentistry, 46CP (ceramic primer), 193, 194, 203Crown

contour, 153–5form, 153lengthening, 29, 99, 102, 146margins, 128–30, 136, 137, 153, 154, 146, 153,

160, 175, 178, 187, 194metal–ceramic, 55, 58, 59, 69, 193, 195preparation, 136, 196

Crown-to-tooth interface, 28, 29CT scan, 3–5Curing, see light curingCuspal coverage, 99Cutting efficiency, 135, 136Cyclic deformation, 117Cyclic loading, 193, 195

DDaylight, 85, 86, 95, 95De-lamination, 65, 69, 70, 73Dental aesthetics, 37–52Dental articulator, see semi-adjustable articulatorDental midline, 43, 148Dental tape/floss, 161, 204Dentine bonding agents (DBAs), 58, 99, 100, 121,

132, 135, 137, 141, 151, 160, 162, 178, 192

bonding, 198, 199efficacy, 201–202etching, 198, 199generations, 199–200mechanism, 197–9monomers, 198, 200

priming, 198, 199solvents, 200–201, 207

Dentine tubulesblock, 151, 160seal, 151, 178, 199

Dentinedesensitise, 151disinfect, 151moist, 201sclerotic, 204

Dentogingival complex, 24, 29, 138Detector, 81Diagnosis, 3, 13

2D, 43D, 4–5

Diagnostic wax-up, 3, 10, 13, 31, 32, 159, 162

Diamond grits, 133–4, 135Diastema, 43, 136, 138, 148Dicor, 70Dies, 187, 188Difference threshold, 87Digital camera, 94Dimensional stability, 166, 169, 179Discolouration, 67, 83, 103, 110, 118, 126, 128,

132, 147, 157, 196, 201Dispersion strengthening, 63Dominance, 46

EElastic recovery, 169Electromagnetic spectrum, 78Electrosurgery, 168E-mail, 96Emergence profile (EP), 130, 153, 154, 160, 174,

175, 176, 179, 182, 187, 188, 189Empress 1, 62, 64, 70, 92, 110, 196, 205Empress 2, 63, 65, 92, 110, 113, 186, 196, 205Enamel

cracks, 133lip, 131lustre, 93overlay, 88–9, 94texture, 93thickness, 93translucency, 93

Epithelial attachment (EA), 24, 26Erosion, 110Etching, 194, 197Ethanol, 200–201Evidence-based decisions, 6–9, 15Evidence-based treatment, 7–9, 12–19, 15Examination, 2, 12

214 Index

Examinationaesthetic, 2occlusal, 2tactile, 2visual, 2written, 2

Exothermic setting reaction, 151, 152, 156, 157,159

Explicit representation, 84

FFacebow, 179, 180, 186Facial midline, 39Facial profile, 41Failure rate, 69Ferrule effect, 99, 106, 107, 116, 118Fibre, 105, 151Filler, 153, 157Fill-in, 101Finish line, see crown marginsFinite element analysis, 130Fixed partial denture (FPD), 65, 68, 69, 70, 107,

127, 149Flexural strength, 58, 62, 105, 151, 156, 195Flowable composites, 101, 102, 108, 109, 120, 121,

157, 159, 161Fluorescence, 89–90, 93, 94, 96, 189Fluoride release, 110, 192Fovea, 82, 96Fracture, 33, 34, 59–60, 101, 102, 106, 114, 125,

132, 185, 186, 195, 202Fracture resistance, 104, 105, 109, 192, 195, 196Fracture toughness, 58, 59, 60, 151, 156, 157,

192Free gingival margin (FGM), 22, 24, 29, 127, 129,

136, 137, 146, 150, 153, 174, 175, 188, 189

Fulcrum, 43

GGates-Glidden burs, 119Geometric laws, 38Gingiva, 22Gingival aesthetic line (GAL), 50–51Gingival

asymmetries, 50contour, 50, 188, 189cord, see retraction cordcrevice (sulcus), 24, 129curettage, 168exposure, 49recession, 28, 127, 146, 168retraction, 169

scallop, 27, 147, 150zenith, 48, 148

Glass-infiltrated alumina, 65Glass-infiltrated magnesium alumina, 65Glass ionomers, 100–101, 192Glazing, 141, 185, 195Gloves, 170, 182Glycerine gel, 137, 178Golden proportion, 46, 47Grafts, soft tissue, 146Greyscale, 79Griffith’s flaws, 59Grooves, 99, 102, 103, 121, 141Group function, 32Gummy smile, 48

HHaemorrhage-free, see non-haemorrhagicHaemostatic agents, 169, 178, 182Hardness, 58Health, function, aesthetic (HFA) triad, 21, 69, 98,

125, 142, 145Hering’s opponent-process theory, 83, 86Histories, 2–3, 12

dental, 2medical, 2nutritional, 2

Horizontal symmetry, 39, 43Hue, 79, 82, 88, 91, 94, 96Hue bias, 86Hybrid layer, 151, 152, 192, 194, 197, 198, 201,

204Hydrofluoric acid, 58, 59, 199, 202Hydrophilic, 169, 170, 192, 197Hydrophobic, 172, 197Hydroxyapatite crystals, 200Hygroscopic expansion, 192

IId, 38Imbrications, 148Implants, 8, 15, 23, 24, 29–30, 146, 171, 205, 207Implicit representation, 84Impression materials

addition silicones, 171–2condensation silicones, 170irreversible hydrocolloids, 169polyethers, 170–71polysulphides, 169properties, 170–71reversible hydrocolloids, 169

Impression trays, 166, 167Impressions, see biological impressions

Index 215

Impressionsinter-arch, 166intra-arch, 166

Incandescence, 89In-Ceram Alumina, 65, 70In-Ceram Spinell, 65Incisal embrasures, 46, 148Incisal plane, 39, 43, 125, 126, 127, 148Incisal translucency, 189Inlays, 62, 65, 140, 172Insipid, 171Intaglio (fitting) surface, 58, 69, 73, 187, 192, 194,

207pre-treatment, 197, 202–204, 205

Interdental papilla, 48Interferences, 30, 31, 32, 193–4Interpupillary line, 39, 189Iris, 81Isaac Newton, 78

JJust noticeable difference (JND), 87

KKinaesthetic sense, 135

LLARS factor, 41Lateral excursions, 32–3Lens, 81Leucite-reinforced glass ceramic, 58, 62Light curing, 202, 204, 206Light interaction, 55Light transmission, 110, 118, 120Lithium disilicate glass ceramic, 63Long epithelial attachment, 25Longevity, 58, 69, 195Lost-wax process, 61, 63, 70, 103, 135Lubricant, 121Luminescence, 89Lustre, 89, 93, 94Luting agents, see cements

MMakeover, aesthetic, extreme, 11, 45Mamelons, 94Margin geometry, 130, 194Margin integrity (marginal opening, MO), 130, 131,

146, 195Marginal integrity, 63, 146, 152, 156, 157, 160,

187, 189, 192, 201Marginal opening (MO), see marginal integrityMasking, 118

Mastication, 33, 194Material interfaces, 110, 113, 114Metamerism (object and observer), 85–6, 94Microabrasion, 110Microleakage, 99, 101, 102, 114, 115, 119, 146,

151, 152, 195, 196, 197Micromechanical retention, 107, 193, 194, 198,

202Milling, 65, 202Minimal threshold, 87Modulus of elasticity (MOE), 58, 60, 102, 104, 105,

115, 116, 151, 157, 195, 197Monobloc, 108, 113Monomer, 137, 151, 153, 156, 157, 160, 161, 163,

170Morphopsychological, 45Munsell system, 80, 86, 92Muscular activity, 33–4

NNasolabial angle, 40Negative space, 44Neuromuscular adaptation, 32, 36Neuromuscular learned behaviour, 31Neuromuscular programming, 35Neutral grey, 86, 87, 96Non-haemorrhagic, 174–7Non-working side contacts, 31–2

OObturation, 119Occlusal vertical dimension (OVD), 34–6, 125, 126,

158Occlusion, 30–36, 147, 167, 204

anterior guidance, 147centric occlusion (CO), 31, 160, 167, 188, 189centric relation (CR), 31, 147, 167, 188, 189non-axial, 103, 108, 114, 118, 131, 193parafunction, 140stress, 66, 101, 103, 116, 194, 195

Onlays, 62, 65, 99, 172Opalescence, 90, 93, 94, 96Optical connectivity, 190Optical

capacity, 56–7properties, 58

Oral hygiene, 153, 174Orthodontic extrusion, 99, 102, 146Ovate pontic, 146, 147, 149Overbite, 148Over-contour, 153–5, 175, 181, 189Over-contouring, 130, 188Oxygen blocking gel, 204

216 Index

Oxygen inhibition layer, 146, 163, 178, 204Ozone layer, 89

PPapilla, 48, 147, 181, 188Parabolic implant, 30Passive eruption, 26Passive seating, 160, 187, 204Peeso drills, 119Perfect smile, 38, 45Peri-implant tissue, 29Perikymata, 186Periodontal

bioform, 26–8, 148, 173biotype, 26–8, 173, 175, 207health, 173ligament, 25, 30pockets, 127, 128

Periodontium anatomy, 22Petroleum jelly, 160, 162, 163Phase separation, 207Phase transformation, 68Phonetics, 36–7, 147, 189Phosphoric acid, 151, 198, 199, 202, 204Photographic documentation, 94Pink aesthetics, 51, 130, 150, 179Pins, 99, 103, 140Plaque, 153, 155Polishing, 153, 157, 161, 185, 188, 207Polymerisation shrinkage, 102, 152, 156, 157, 166Polyvinyl siloxanes, see impression materials,

addition siliconesPorcelain fused to metal crown (PFM), 70Porcelain laminate veneer (PLV), 62, 132Porcelain

feldspathic, 58, 61, 110low-fusing, 58optical properties, 89, 90veneering, 57

Post canalmodifying, 119shapes, 119

Post-operative sensitivity, 102, 135, 151, 152, 160,195, 196, 197

Postsactive (threaded), 107aesthetics, 110–113ceramic, 104, 114, 117, 172diameter, 117dislodgement, 114, 115failures, 115fibre, 104, 104fractures, 115–16

length, 117light transmitting, 108, 110–111, 112, 120, 172parallel, 106passive, 103, 107placement, 117–21plastic, 121prefabricated, 109, 115retention, 115selection, 114stiffness, 116tapered, 106temporary, 121

Previser risk calculator, 6Primary colours, 80, 94Primer, 151Procera, 66, 70, 110, 132, 136, 140, 141, 142, 186,

193, 196, 202, 205Prophylaxis, 137, 138, 174Proportions, repeating, 46Proprioceptive response, 98Psychophysics, 77Pulpal necrosis, 133–4, 152, 163Pupil, 82Pythagoras, 46

RRadiant energy, 78, 81Radiating symmetry, 43Radiolucency, 105Radiopaque, 104Reciprocating handpiece, 131Relative shade analysis, 94, 96Resin cements, adhesive, 59Resistance, 99, 131, 146, 194Retention, 99, 131, 145, 194, 196Retina, 81Retraction cord, 118, 119, 121, 127, 129, 137, 138,

160, 168, 175, 176, 201, 203, 204, 207double cord technique, 178–9

RGB devices, 94Rickett’s E-plane, 40Risk assessment, 3, 15, 173Rods, 82, 96Root canals, 107Root fractures, 116–17Roots, 109Rubber dam, 102, 103, 107, 118, 119, 121, 141,

201

SScalloped implant, 30Scanning, 66, 74Segregative forces, 39

Index 217

Semi-adjustable articulator, 167, 180, 186, 189Sensory adaptation, 87Separating medium, 121, 160, 162Sex, age, personality (SAP), 46Shade analysis, 84, 85, 87, 91–6

instrumental, 93–4, 96invariant pair, 85ocular, 95–6, 146

Shade guides, 90–93limitations, 93

Shear bond strength (SBS), see bond strengthShear stresses, 108, 118Shim stock, 188, 190Silane, 58, 193, 194, 203, 205Sintered, 62

complete, 68densely, 66, 69partially, 65pre-, 69

Slots, 99, 141Smear layer, 151, 160Smile line, 44Smile symmetry, 45Smoking, 173Spectral curves

power distribution, 78, 85reflectance, 79, 80, 85, 94response, 83sensitivity, 80transmittance, 80, 85, 94

Spectrophotometer, 80, 94Splinting, 147Staining, see discolourationStatic fatigue, 59Stomatognathic system, 32, 33Stress corrosion, 59Study models, 2Substructure, 58Success rate, 69, 106Surface roughness, 135, 146, 147, 155, 202Surface sealant, 163Survival rate, 69, 70, 106, 127Systematic approach, 2

TTaper, 132, 194, 196Tear resistance, 169, 172Technological tests, 2, 13Technique sensitive, 200Temporo-mandibular joint (TMJ), 21, 32–4Tensile strength, 132, 192Tetracycline staining, 83, 110Texture, 93, 94, 125, 189

Therapeutic temporary restorations (TTR), 119,135, 137, 141, 174, 185, 189, 203

cements, 161fabrication

direct–indirect technique, 162direct technique, 160–61indirect technique, 162

materialsbis-acrylic resin composite, 157bis-GMA resin, 157fabrication, 157–63metal, 159plastic, 159polymethyl methacrylate (PMMA), 156polyvinyl ethylmethacrylate (PVEMA), 156–7properties, 155–7selecting, 161urethane dimethacrylate (UDMA), 157

matrices, 158polishing, 161reinforcement, 151, 162surface sealant, 162

Thermocycling, 193, 194, 195Thickness, bucco-lingual, 46Tooth

morphology, 46, 147, 157preparation, 132, 136, 146reducation, 132, 136size, 45triune, 133

Tooth-to-tooth progression, 46Transduction, 81Transillumination, 102Transmucosal support, 181, 182, 187, 189, 207Tray adhesive, 178, 181, 182Treatment objectives, 15Treatment plan proposals, 9Treatment planning, 3, 11, 13, 16Treatment success, 22Try-in, 16, 18, 207

bisque bake, 141, 142, 181, 188extra-oral, 186–8intra-oral, 189–90

UUltra-sonic bath, 205Ultra-violet, 79, 89, 96, 197Under-contour, 153–5, 175, 181, 189Undercuts, 99Uni-dose, 207

VVacuum-formed matrix, 159, 162

218 Index

Value, 79, 82, 87, 94, 96Value

high, 68, 83, 89, 93, 111, 186low, 79, 88, 89

Viscoelastic distortions, 181Viscosities, 171Viscous flow, 195Visible spectrum, 78Vision, 82–3Visual acuity, 82Visual capture, 77Visual cortex, 83–4Vita 3D-Master shade guide, 81, 91Vita Classic shade guide, 91Volatile, 200, 207

WWater, 200Wavelength, 79Wax pattern, 108, 109Wear, 33, 39, 58, 66, 102, 142, 147, 192Width/length ratio, 45Working side contacts, 31–2Working time, 168

YYoung–Helmholtz trichomatic theory, 83

ZZekrya gingival protector, 138, 142Zirconia, 68–9, 73, 110, 196, 203

protocols for-predictable-aesthetic-dental-restorations

Health & Medicine

dental composition

dental organisations

treatment planning assessment

ahmad blackwell munksgaard

blackwell publishing

blackwell publishing

blackwell munksgaard

ridgeway dental surgery