Implant quality scale : Osseointegration, success criteria and basic guides

Definitions

Mechanism of osseointegration

Factors effecting osseointegration

Methods of evaluation of

osseointegration

Osseointegration

Bone implant interface

Fibro – osseous integration

Success criteriaSuccess Survival,

And failureEvaluation of

dental Implants

HISTORICAL REVIEW•The concept of osseointegration was developed

and the term was coined by Dr. Per-Ingvar Branemark, Professor at the institute for Applied Biotechnology, University of Goteborg, Sweden

.

Definitions

“The apparent direct attachment or connection of osseous tissue to an inert, alloplastic material without intervening connective tissue”. - GPT 8

Structurally oriented definition

“Direct structural and functional connection between the ordered, living bone and the surface of load carrying implants”.

- Branemark and associates (1977)

Histologically Direct anchorage of an implant by the formation of bone directly on the surface of an implant withoutany intervening layer of fibrous tissue.

- Albrektson and Johnson (2001)

Clinically

Ankylosis of the implant bone interface.“Functional ankylosis” -Schroeder and colleagues 1976

“It is a process where by clinically asymptomatic rigid fixation of alloplastic material is achieved and maintained in bone during functional loading”

- Zarb and T Albrektson 1991

Biomechanically oriented definition

“Attachment resistant to shear as well as tensile forces”

- Steinmann et al (1986).

Bone physiology

Bone can be classified as • Compact bone • Spongy bone

Depending on age, developmental age, localization and function, bone consists of three tissue types that differ in collagen fibril arrangement and mineral content.

Woven bone Lamellar bone Bundle bone

Woven bone• Formed by the osteoprogenitor cells in the vicinity

of blood vessels during prenatal

development ,growth and healing .

• Forms 30-50 µm /day

• High cellular osseous tissue

• Low mineral content

• More pliable than mature lamellar bone

• Capable of stabilizing an unloaded implant,woven

bone lacks the strength to resist functional loads .

Woven bone

Lamellar bone • Principle load-bearing tissue

• Predominant component of mature cortical and

trabecular bone

• Forms relatively slow (< 1.0µm/day)

• Have highly organized matrix, and are densely

mineralized

• Orientation of the collagen fibrils differs from one

layer to another .

Lamellar bone

Bundle bone

• Found in the area of ligament and tendon attachment

along the bone-forming surfaces.

• Striation are extension of sharpey’s fibers composed of

collagen bundles from adjacent connective tissue that

insert directly into the bone

• It is formed adjacent to the periodontal ligament of

physiologically drifting teeth.

Bundle bone

Modelling

• A surface specific activity that produces a net change in

the size and/or shape of bone .

• An uncoupled process, meaning that cell activation(A)

proceeds independently to formation(F) or resorption(R)

• Generalized change in overall dimension of a bone’s

cortex or spongiosa

• Modelling is a fundamental mechanism of growth ,

atrophy and reorientation.

Bone Remodeling

• It is the turnover or internal restructuring of previously existing bone .

• Coupled tissue level phenomenon

Bone to implant interface There are two basic theories

Osseointegration(Branemark 1985)

Fibro-osseous integrationLinkow 1976James 1975Weiss 1986

FIBROINTEGRATION OSSEOINTEGRATION

In 1986, the American Academy of Implant Dentistry (AAID)

“Tissue-to-implant contact with healthy dense collagenous tissue between the implant and bone”

Fibro-osseous integration

Presence of connective tissue between the implant and

bone

Collagen fibers functions similarly to Sharpey’s fibers

found in natural dentition.

The fibers are arranged irregularly, parallel to the implant

body, when forces are applied they are not transmitted

through the fibers

Weiss concept Collagen fibers at the interface - peri-implant membrane

with an osteogenic effect. Collagen fibers invest the implant, originating at the

trabeculae of cancellous bone on one side, weaving around the implant, and reinserting into a trabeculae on the other side.

It was felt that, this membrane gave a cushion effect and acted as similar as periodontal membrane in natural dentition.

Failure of fibro-osseous theory

No real evidence Forces are not transmitted through the fibers -

remodeling was not expected Forces applied resulted in widening fibrous

encapsulation, inflammatory reactions, and gradual bone resorption there by leading to failure.

Natural teeth ImplantOblique and horizontal group of fibers

Parallel, irregular, complete encapsulation

Uniform distribution of load (Shock absorber)

Difficult to transmit the load

Failure : Inability to carry adequate loads -

Infection

Osseointegration

American Academy of Implant Dentistry (AAID) defined it as

"contact established without interposition of non-bone tissue

between normal remodeled bone and an implant entailing a

sustained transfer and distribution of load from the implant

to and within the bone tissue"

Mechanism of Osseointegration

• Healing process may be primary bone healing or secondary bone healing.

• In primary bone healing, there is well organized bone formation with minimal granulation tissue formation - ideal

• Secondary bone healing may have granulation tissue formation and infection at the site, prolonging healing period. Fibrocartilage is sometimes formed instead of bone - undesirable

Blood between the fixture and bone

Blood clot

Procallus (contains fibroblast)

Callus (contains osteoblast)

Bone

Remodelling

Phagocytic cellsPMNL

Mechanism of osseointegration

Phase Timing Specific occurrence 1.Inflammatory

phase Day 1-10 Adsorption of plasma proteins

Platelet aggregation and activation

Clotting cascade activation Cytokine release

Specific cellular inflammatory response

Macrophage mediated inflammation.

Phase Timing Specific occurrence

2. Proliferative phase

Day 3 - 42 NeovascularizationDifferentiation,

Proliferation and activation of cells.

Production of immature connective tissue

matrix.

Phase Timing Specific occurrence

3.Maturation phase

After Day 28

Remodeling of the immature bone matrix with coupled resorption and deposition of bone.

Bone remodeling in response to implant loading

Bone tissue response

• Distance Osteogenesis

A gradual process of bone healing inward from the edge of the osteotomy toward the implant. Bone does not grow directly on the implant surface.

• Contact Osteogenesis

The direct migration of bone-building cells through the clot matrix to the implant surface. Bone is quickly formed directly on the implant surface.

Mechanism of integration: (Davies - 1998)

Contact osteogenesis :

Early phases of osteogenic cell migration (Osteoconduction)

De novo bone formation Bone remodeling at discrete sites.

Osteoconduction

“Osteoconduction” refers to the migration of differentiating osteogenic cells to the proposed site.

Migration of the connective tissue cells will occur through the fibrin that forms during clot resolution.

The migration of cells through a temporary matrix such as fibrin - retraction of the fibrin scaffold.

De novo bone formation

Differentiating osteogenic cells, which reach the implant surface initially, secrete a collagen-free organic matrix that provides nucleation sites for calcium phosphate mineralization

Noncollagenous bone proteins - Osteopontin and bone Sialoprotein

Bone bonding in de novo bone formation

Bonding of de novo bone will occur by the fusion, or

micromechanical interlocking of the biologic cement line

matrix with the surface reactive layer

Bone remodeling

During the long-term phase of peri-implant healing, it is only

through those remodeling osteons that actually impinge on

the implant surface that de novo bone formation will occur

at these specific sites on the implant

Stages of Osseointegration

According to Misch there are two stages in osseointegration, each stage been again divided into two substages. They are:

Surface modeling Stage 1: Woven callus (0-6 weeks)Stage 2: Lamellar compaction (6-18 weeks) Remodeling, Maturation Stage 3: Interface remodeling (6-18 weeks)Stage 4: Compact maturation (18-54 weeks)

Stage 1: Woven callus0-6 weeks of implantation.

Woven bone is formed at implant site.

Primitive type of bone tissue and characterized

Random, felt-like orientation of collagen

fibrils

Numerous irregularly shaped osteocytes

Relatively low mineral density

Stage 2: Lamellar compaction

6th week of implantation and continues till 18th week. The woven callus matures as it is replaced by lamellar

bone. This stage helps in achieving sufficient strength for

loading.

Stage 3: Interface remodeling

This stage begins at the same time when woven callus is

completing lamellar compaction. During this stage callus starts to resorb, and remodeling

of devitalized interface begins. The interface remodeling helps in establishing a viable

interface between the implant and original bone.

Stage 4: Compact bone maturation

This occurs form 18th week of implantation and continues till the 54th week.

During this stage compact bone matures by series of modeling and remodeling processes.

The callus volume is decreased and interface remodeling continues.

Six different factors known to be important for the establishment of a reliable, long-term osseous anchorage of an implanted device

Implant biocompatibility Design characteristics Surface characteristics State of the host bed Surgical technique and Loading conditions

Implant Biocompatibility

Chemical interaction determined – properties of surface oxide

Commercially pure (c.p.) Titanium and Titanium alloy (Ti -6AL-4V)

Documented long term function Covered with adherent, self- repairing oxide layer Excellent resistance to corrosion – high dielectric

constant Load bearing capacity

Other metals Niobium, tantalum Cobalt chrome molybdenum alloys Stainless steels Ceramics - calcium phosphate hydroxyapatite (HA) and

various types of aluminium oxidesBiocompatible - insufficient documentation and very less

clinical trials - less commonly used.

Degree ofCompatibility

Characteristics of Reactions of Bony Tissue

Materials

Biotolerant Implants separated from adjacent bone by a soft tissue layer along most of the interface: distance osteogenesis

Stainless steels: CoCrMo and CoCrMoNi alloys

Bioinert Direct contact to bony tissue contact osteogenesis

Alumina ceramics, zirconia ceramics, titanium, tantalum, niobium, carbon.

Bioactive Bonding to bony tissue: bonding osteogenesis

Calcium phosphate-containing glasses, glass-ceramics, ceramics, titanium (?)

Grouping of hard tissue replacement materials according to their compatibility to bony tissue

Implant Design (Macrostructure)

Threaded or screw design implants Promote osseointegration More functional area for stress distribution

than the cylindrical implants. Minimal - <0.2 mm/year bone loss

Cylindrical implants Press fit root form implants depend on

coating or surface condition to provide microscopic retention and bonding to the bone

Bone saucerization

Non threaded

•Tendency for slippage•Bonding is required

•No slippage tendency•No bonding is required

Threaded

Functional surface area per unit length of implant may be modified by the three thread geometry parameters

• Thread shape• Thread pitch • Thread depth

Grooves on the threads of all implants and on the collars, wherever appropriate.

Increase surface area Increase area for bone-to-implant contact

Implant Surface (Microstructure,Surface Topography)

“The extent of bone implant interface is positively correlated with an increasing roughness of the implant surface”

Roughened surface

Greater bone to implant contact at histological level Micro irregularities - cellular adhesion. High surface energy - improved cellular attachment.

• Roughness parameter (Sa)0.04 –0.4 m - smooth 0.5 – 1.0 m – minimally rough 1.0 –2.0 m – moderately rough 2.0 m – rough

• Wennerberg (1996) – stated that moderately rough implants developed the best bone fixation.

Smooth surface < 0.2 m will – soft tissue no bone cell adhesion clinical failure.Moderately rough surface more bone in contact with implant better osseointegration.

Surface treatments

Turned surfaceSandblasted surfaceAcid etched surfaceTitanium plasma spraySandblasting and surface etchingHydroxyapatite coatingsAnodized surface

Bone – implant contact areaSurface treatment 1 month 3 months 6 months

Machined/ truned 42% 44%

Machined/ sandblasted 54%

Machined/ acid etched 42% 51% 49%

Sandblastedand acid etched

58%

72%

52%

68%Oxidized 35% 43%

Titanium plasma-sprayed 52% 78%

Hydroxyapaptite 79%Ion implantation 68% 61%

Laser treated 38%

State of the host bed Ideal host bed Healthy and with an adequate bone stock Bone height Bone width Bone length Bone density

Undesirable host bed states for implantation Previous irradiation Ridge height resorption Osteoporosis

Implant bed - Bone QualityAccording to Lekholm and Zarb,1985

• Quality I composed of homogenous compact bone found in the lower anterior

• Quality II Thick layer of cortical bone surrounding dense trabecular bone found in the lower posterior

Quality III Thin layer of cortical bone surrounding dense trabecular bone – upper anterior and upper

& lower posterior region

Quality IV Very thin layer of cortical bone surrounding a core of low-density trabecular bone - very soft bone found in the upper anterior and posterior

Branemark system (5 year documentation) Mandible – 95% success Maxilla – 85-90% success

According to Branemark and Misch D1 and D2 bone initial stability / better osseointegration

D3 and D4 poor prognosis

D1 bone – least risk

D4 bone - most at risk

Selection of implant D1 and D2 – conventional threaded implants

D3 and D4 – HA coated or Titanium plasma coated implants

Surgical Considerations

Promote regenerative type of the bone healing rather than reparative type of the bone healing.

The critical time/ temperature - bone tissue necrosis - 47° for one minute.

Recommendations Slow speed Graded series Adequate cooling Bone cutting speed of less than 2000 rpm Tapping at a speed of 15 rpm with irrigation Using sharp drills The optimal torque threshold – 35 N/cm. Implant should gently engage the bone in order to avoid

too much pressure at the bone interface which could jeopardize healing

Surgical skill / technical excellence

Progressive or two stage loading

Branemark et al to accomplish osseointegration

considered the following prerequisites

Countersinking the implant below the crestal bone

Obtaining and maintaining a soft tissue covering over

the implant for 3 to 6 months

Maintaining a non loaded implant environment for 3 to 6

months

Delayed loading: - Two-stage surgical protocol

- One-stage surgical protocol

Immediate loading:1. Immediate occlusal loading (placed within 48 hours)

2. Immediate non-occlusal loading (in single-tooth or short-span applications)

3. Early loading (within two months)

Frost’s mechanostat theory

Systemic factors

Active chemotherapy Type 2 (late-onset) diabetes: This is especially the

case where this is not well controlled

Treatment by an operator with limited surgical experience.

Patients who were smokers at the time of implant surgery had a significantly higher implant failure rate (23.08%) than non-smokers (13.33%)

Short implants and implant placement in the maxilla were additional independent risk factors for implant failure.

DeLuca S, Habsha E, Zarb GA. The effect of smoking on osseointegrated dental implants. Part I: implant survival. Int J Prosthodont 2006;19(5):491-8

Subjective criteriaAdequate functionAbsence of discomfortImproved aestheticsImproved emotional and psychological wellbeing

Harvard success criteriaThe dental implant must provide functional service for 5 years in 75% of cases

Objective criteria

Bone loss no greater than 33% of vertical length of implant

Gingival inflammation amenable to treatment

Mobility of less than 1mm in any direction

Absence of symptoms of infection

Absence of damage to surrounding structure

Healthy connective tissues

Possible criteria for success

MobilityPeri-implant radiolucencyMarginal bone lossSulcus depthGingival statusDamage to adjacent teethViolation of maxillary sinus , mandibular canal

or floor of nasal cavityAppearanceLength of service

Condition for application of criteria

Only osseointegrated implants should be evaluated with these criteria.

The criteria apply to individual endosseous implants.

At the time of testing, the implants must have been under a functional load.

Implants that are beneath the mucosa and in a state of health in relation to the surrounding bone should preferably not be included in the evaluations but reported as complications.

Complications of an iatrogenic nature that are not attributable to a problem with material or design should be considered separately when computing the percentage of success

Revised criteria - Albrektsson

Individual implant is immobile clinically

No evidence of peri-implant radiolucency is present as assessed on an undistorted radiograph.

Mean vertical bone loss is less than 0.2 mm annually after the first year of service.

No persistent pain, discomfort, or infection is attributable to the implant.

Implant design does not preclude placement of a crown or prosthesis with an appearance that is satisfactory to the patient and dentist.

By these criteria, a success rate of 85% at the end of a 5-year observation period and 80% at the end of a 10 year period are minimum levels for success.

Drago et al

anterior maxilla-89.1%

posterior maxilla-71.4%

anterior mandible-96.7%

posterior mandible-98.7%

Success rate

Moy et al –

maxilla-91.8% mandible-95.1%

Bass et al –

maxilla-93.4% mandible-97.2%

5-year survival

conventional tooth-supported FDPs of 93.8%

cantilever FDPs of 91.4%

solely implant supported FDPs of 95.2%

combined tooth-implant-supported FDPs of 95.5%

implant supported SCs of 94.5%

FDP vs Implants

After 10 years of function –

89.2% -conventional FDPs

80.3% -cantilever FDPs

86.7%- implant-supported FDPs

77.8% - combined tooth-implant-supported FDPs

89.4% - implant-supported SCs

Technical complications were (fractures of the veneer

material, abutment or screw loosening and loss of

retention)

Methods of evaluation of Osseointegration

Stability is a requisite characteristic of osseointegration.

Initial stability is a function of the Bone quality, Implant design and Surgical technique.

During the osseointegration healing and maturation process , the initial stability changes with increases in bone- to –implant contact and osseous remodeling.

Invasive Methods

Histological sections (10 microns sections)

Histomorphometric – To know the percentage of bone

contact

Transmission electron microscopy

By using Torque gauges

Non-Invasive Methods Percussion test Tapping with a metallic instruments

Ringing sound- osseointegrated. Dull sound - fibrous integration.

Radiographs

Reliable method to determine implant stability

Emg driven and electronically controlled

tapping head that hammers an object at a

rate of 4 times/sec

Periotest

Response to striking is measured by a small

accelerometer present in head

Signals converted to periotest value

Depends on damping characteristic of tissues

surrounding teeth or implant

Developed by Aoki and Hirakawa

Mech is similar to periotest

Microphone used as receiver and signals

transferred is processed by FFT for analysis

Dental mobility checker

Non invasive can be performed at any stage of

healing

Bite wing-measure crestal bone level

1.5 mm of CBL can be expected in the Ist year of

loading with 0.1 mm of subsequent annual bone

loss

Radiographic evaluation

Problems

Difficult for clinician to detect changes at 0.1mm

resolution

Can be measured when central ray of x-ray is

perfectly ll with the structure of interest

Excellent method to assess health of natural teeth

In implants little diagnostic value unless accompanied by signs & symptoms

Stable implants pocket depth- 2-6mm

Indicate bone loss but not necessarily disease

Sulcus depth greater than 5-6 mm-risk of anaerobic bacterial infection

Probing depth

Suggested by James, modified by Misch

Group I Group II Group III Group IV

Misch CE, Perel ML, Wang HL, et al. Implant success, survival, and failure: The International Congress of Oral Implantologists (ICOI) Pisa Consens Conference. Implant Dent 2008;17:5-15.

Implant quality of health scale

No pain or tenderness upon function

0 Mobility

Less than 2.0 mm crestal bone loss from initial surgery

No history of exudate

Group I (Success)

No pain on function

0 mobility

Crestal bone loss – 2 to 4 mm

No history of transient exudate

Prognosis good to very good

Group II (survival-satisfactory health)

Slight to moderate peri-implantitis

Sensitivity on function

Radiographic bone loss > 4 mm (<1/2 of implant

body)

No mobility (IM-O)

Probing depth >7 mm

May have exudates history

Group III (Survival-compromised health)

Implant removed Pain mobilityUncontrolled progressive bone loss;Uncontrolled exudate50% bone losssurgically removed/ exfoliated

Group IV(clinical or absolute failure)

Rigid fixation

Scale

Description

0 Absence of clinical mobility with 500g in any direction

1 Slight detectable horizontal movement

2 Moderate visible horizontal mobility up to 0.5 mm

3 Sever horizontal movement greater than 0.5 mm

4 Visible moderate to sever horizontal and any visible vertical movement

Cutting Torque resistance analysis (CRA)

Reverse Torque test (RTV)

Resonance Frequency analysis (RFA)

Other methods

Johansson and strid and improved by Friberg et al

Energy required for a current fed electric motor in cutting off a unit volume of bone during surgery is measured.

Energy is correlated with bone density which influences the implant stability

Cutting Torque resistance analysis (CRA)

Torque guage-in drilling unit measures the insertion torque in Ncm, gives idea about the bone quality

Gives more objective assessment than clinician dependent evaluation

Advantages

a. Detect bone density

b. Identify bone density during surgery

c. Can be used in daily practice

Disadvantages

d. can only be used during surgery

e. longitudinal data cannot be collected to assess

bone quality changes after implant placement

Measures the ‘critical’ torque threshold where

bone-implant contact (BIC) was destroyed

Removal Torque value (RTV)-indirect

measurement of BIC/clinical osseointegration

Reverse Torque test (RTV)

Ranges from 45-48 Ncm

RTV >20 Ncm accepted as criteria for

successful osseointegration

Varies depending on bone quality & quantity

Disadvantages

a. RTV only provide information as to “all or

none” outcome

b. Mainly used in experiments

Non invasive method that measures implant stability & bone density at various time points

RFA utilizes a small L-shaped transducer that is tightened to implant or abutment

Resonance Frequency analysis (RFA)

Transducer comprises of 2 piezoceramic elements

One for vibration, and other serves as a receptor

for the signal

Resonance peaks from the received signal

indicates the first RF of the measured object

Earlier hertz was used as measurement unit

now implant stability quotient (ISQ)

RF values ranging from 3500-8500 Hz

translated into ISQ of 0-100

Higher value-greater stability

Low value-instability

Successful implant-ISQ >65

ISQ <50 indicates potential failure/increased risk

of failure

RFA can only give information regarding success

cannot provide information with respect to survival

or failure.

ISQ is fairly reliable when implant has achieved

osseointegration & the B-I interface is rigid.

ISQ tends to fluctuate when the interface is not rigid

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Mosby Elsevier publication, St Louis, 2008, pp:27, 70, 621

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Masuda T, Yliheikkilä PK, Felton DA, Cooper LF. Generalizations Regarding the Process and Phenomenon of Osseointegration. Part I. In Vivo Studies. Int J Oral Maxillofac Implants 1998;13:17–29

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DeLuca S, Habsha E, Zarb GA. The effect of smoking on osseointegrated dental implants. Part I: implant survival. Int J Prosthodont 2006;19(5):491-8

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http://www.ecf.utoronto.ca/~bonehead/