cast restorations
TRANSCRIPT
CAST RESTORATIONS-INTRODUCTION
Deepthi P.R.2nd Year MDS
Dept. of Conservative Dentistry & Endodontics
History Indications Contraindications Advantages Disadvantages Materials for cast restorations Mouth preparation prior to cast restorations
CONTENTS
Metal casting : Lost wax/ “Cire perdue” method Agiulhon de Saran in 1844: Inlay in
investment mold with molten Gold B.F. Philbrook: simplified version of casting
process in 1897 Many techniques: flowing solder into molds for
gold inlay fabrication Porcelain inlays : 1857; later replaced by the
cast gold inlays
HISTORY
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William Taggart in 1907: Technique of fabrication of gold castings
Paralleling systems: 1890s Centrifugal casting machine : Jamieson in 1907 1985: first ceramic inlay CAD/CAM
Extensive tooth involvement Adjunct to successful periodontal therapy Correction of occlusion/ Diastema closure Endodontically treated teeth Support for and preparatory to partial or
complete dentures Retainers for fixed prostheses
INDICATIONS
Partially subgingival restorations Low incidences of plaque accumulation or
decay Functionally sound stomatognathic system
with complete freedom of the mandible to move without any premature contacts
Cracked teeth Esthetics Dissimilar metals
INDICATIONS
Efficiently replace lost tooth structure Support remaining tooth structure Higher strength & superior control of
contacts and contours Cast metal onlay: withstand & distribute
occlusal loads Amalgam: foundation
Extensive tooth involvement
Contacts & contours, marginal ridges, embrasures: physiologically restored & permanently maintained
Splinting of periodontally weakened teeth by cast restorations
Preserve intact facial and lingual enamel/ cementum
Adjunct to successful periodontal therapy
Dental Update 2000;27:278-285
Linked crowns
Gold copings for telescopic crowns
Endodontically treated teeth
Reinforcement of the clinical crown portion
Onlay : distribute occlusal loads to reduce chances of tooth fracture
Changes in occlusal table or occlusal parts of a tooth
Inlay/ onlay for extension of mesiodistal dimension
Slightly tilted teeth
Correction of occlusion
Abutment teeth: accommodate the retainers for denture
Better accommodation of forces Rest seats, guiding planes better controlled with indirect technique
Partial & Complete dentures- Removable & Fixed
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Functionally sound stomatognathic system
Free of any pathology Pathology: diagnosed
and treated If not expected to be
corrected by cast restorations- correction prior to restoration
Tooth – cement- cast restoration complex: break down avoided
Rigid control of plaque accumulation
Low incidence of plaque accumulation/ decay
Cracks: cleavage planes for possible future fracture
Cast onlays with skirting & crowns: braces tooth against fracture injury
Restoration & splinting of cracked, separated segments of teeth
Healing of some cracks
Cracked teeth
Existing cast restorations
Dissimilar metals
• Galvanism• Premature abrasion
• Anodic dissolution of metals
• Mechanical failure of restorations
Approximating dissimilar metal: diffusion of restorative materials to the cast alloy
Vacancy porosities in the material Alloying of the cast alloy – weaken them
Properly finished and polished cast alloys: most compatible with periodontium
Most practical for subgingival lesions
Partially subgingival restorations
Large pulp chambers & incompletely mineralized dentin
Developing and deciduous teeth: Growth / Resorption affected by traumatic nature of the procedure
High plaque/ caries indices: Recurrent decay & acceleration of periodontal deterioration
Occlusal disharmony Dissimilar metals
CONTRAINDICATIONS
Strength Biocompatibility: Allergic patients Precise detail Corrosion resistance Instantaneous : casting procedure Maximum biological acceptance
ADVANTAGES
Low wear: Castings withstand occlusal loads with minimal changes
Control of contours and contacts: Indirect technique- large & complex restoration
Strength: Yield, Compressive, Tensile & Shear strengths:
greater Replace areas of stress concentration &
reinforce weakened tooth structure Material imparts resistance to the tooth
Instantaneous building: Fewer voids No layering effect Less internal defects Fairly even stress patterns of entire structure
ADVANTAGES
Reproduction: Precise form & minute detail maintained Details maintained under functional stresses
Corrosion Resistance: Noble/ passivated metal Not affected by oral environment Cast ceramics: completely inert Improved longevity, esthetics & biologic
qualities
ADVANTAGES
Biological acceptance: Finished, polished, glazed outside the oral
cavity No risk of heat & pressure to the P-D organ
ADVANTAGES
Number of appointments & higher chair time:
Two appointments & more time than direct restoration Temporary: Loosen or break occasionally Cost: Material costs, laboratory bills & time
involved Technique sensitive: Error in multistep
process – suboptimal fit Splitting forces: Small inlays- wedging
effect
DISADVANTAGES
Several interphases Extensive tooth preparation: hazardous
to vital tissues Galvanic deterioration Abrasion differential
DISADVANTAGES
Several interphases: Tooth- cement- casting junction: leakage Number of reproductions with different
materials Microscopically ill fitting restoration Leakage pronounced gingivally
DISADVANTAGES
Galvanic deterioration: Cathodic nature of alloys to other metals Rapid deterioration of amalgam & failure Cast alloy contamination by free mercury Undesirable effects: vital tissues
DISADVANTAGES
Abrasion Potential: Alloys & ceramics: high abrasive resistance
than enamel Teeth abraded more easily: abrasion differential Imbalance in occlusion: teeth shifting, tilting or
rotating Occlusal interferences Periodic occlusal equilibriation needed
DISADVANTAGES
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ADA#5: 75% Au & Pt based alloys Other castable materials available
MATERIALS USED FOR CAST RESTORATIONS
Types I, II , III, IV
Gold alloys
Low gold
alloys:Au
<50%
Non gold Pd based alloys
Ni- Cr based alloys
Castable moldabe ceramic
s
Use Major elements Nobility Three principal elements Dominant phase system Revised classification by ADA in 2003
CAST DENTAL ALLOYS- Classification
Classification
Use All- metal inlays Crowns & bridges Metal- ceramic
prostheses Posts & cores Removable partial
dentures Implants
Major elements Au based Pd based Ag based Ni based Co based Ti based
Classification
Three principal elements
Au-Pd-Ag Pd-Ag-Sn Ni-Cr-Be Co-Cr-Mo Ti-Al-V Fe-Ni-Cr
Nobility High- noble Noble Predominantly base
metalDominant phase
system Single phase Eutectic Peritectic Intermetallic
Revised classification ADA-2003
High Noble (HN) Ti & Ti alloys Noble (N) Predominantly base
metal (PB)
High Noble (HN) Noble (N) Titanium (TI) Predominantly base
alloys (PB) Cobalt- base alloys
(cobalt base PB)
IdentAlloy system
Baseline of casting alloys 70-75% Au or Pt group substitutes: Pt, Pd,
Rh, Os, Ir, Ru 25-30% : Ag & Cu (hardening) Traces : Zn &/or In 4 types
COMPOSITION & EFFECTS- CLASS I ALLOYS
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Type I: most plastic & highest gold content Type IV: least deformable & the lowest
content of gold Single tooth restoration: Type III/ II Properties: % composition, alloying nature &
environment of fabricating & casting
Au: Alloy in different fashions with each metal
Pd & Pt: Disordered alloying with Au & several ordered alloys with Cu
Ag: Substitutional & ordered alloying with Au ; readily alloy with copper- ordered to eutectic alloys & solid solution with Pd
Cu: Solid solution with Au, Pd, Pt & Ag Zn, In: Alloy with gold
Au: Deformability, strength, hardness, characteristic yellow color & density – 19.3 g/cm3
Pt, Pd: Rigidity, nobility, strength, hardness & whitening of the alloy
Ag: Mimics Au in deformability effect, but adversely affects nobility. Precipitated Ag-Au intermetallic compound: hardening process
Cu: Increases hardness & strength, decreases the nobility
Effects on Properties
Zn: Essential deoxidizer during casting & replaced if the alloy is to be recast
In: refines the grains of the final alloy; scavenger for the alloy during the casting procedure
“ Economy gold alloys” Gold content much lower than Class I Pd: gold substitute 60% Pd & 5% Au; Cu, Ag, Zn: 25-30% Au: same properties but limited Pd: most desirable physical properties Cu: reacts with Pd- strengthening-
hardening-brittling effect Ag: continuous substitutional solid solution
alloy with Pd
CLASS II ALLOYS
Mainly of Pd & Ag with In, Cu, Sn, Zn not >10%
Pd: White color& density – 11g/cm3,
strength, hardness, plasticity & nobility Ag: Substitutional alloys with Pd ; more
plastic, less strength & nobility with increased Ag
CLASS III ALLOYS
Cu: Reacts with Pd & Au; lowers fusing temperature & increased resistance to tarnish & corrosion
Zn: Deoxidizer In: Scavenger during melting , to increase
resistance to tarnish & corrosion
Additions to the basic Ni-Cr combination Cr not >30% Both: Passivity, strength, density (8g/cm3 ) ,
plasticity, hardness & color W, Mo, Al: increase strength & hardness-
ppt intermetallic compounds with Cr & Ni Be: lower the fusion temperature &
improve castability- hazards. Ga- substitute
CLASS IV ALLOYS
Si & Fe: Increase the strength; not >2% C 2- : 0.2 to 0.4% - strengthening of alloy Complex carbides: Ni & Cr- MC, M6 C, M23 C6 B: Reducing the solubility Of C & stabilizing
carbides B & Si: Deoxidisers & flowing agents-
improve castability
CLASS IV ALLOYS
Properties: techniques used in fabrication; carbides incorporated in different stages of casting
Nb: Open air melting of the alloys Sn & rare earth elements : Control oxidation
of alloy during porcelain firing Ti & Co: strength
Complex ceramic monolithic structure: 70-90% crystalline material- Mg aluminate spinel & Alumina
Al2O3 (50%) : MgO (15%) in 7:1 ratio 5-25% glass frit compounded to react with
silica- Silicate glasses Si polymer: workable mass 0.5% stearate/ wax- lubricant
CLASS V ALLOYS
Heated to & above the GTT of polymer binder: 30° to 150 °- plastic, deformable & moldable into Gypsum mold space
Cooling to room temperature: restores the rigidity
Thermal treatment: 10-18 hours- alumina reacts with magnesia forming Mg aluminate spinel – MgAl2O4- expansion
Cations from glass frit & Al2O3- Ionic bonding: metal silicate glasses
Si polymer: R ---O---Si—O—Si--
R 60% SiO group- change to SiO4 with classical
tetrahedron unit cells
Composite material with 4 components
Solid ceramic body with crystalline material:
Thermalprocessing
Al2O3
Mg Al2O4
AlSiO4
Spinel & other crystals & glasses: allotropic & dimensional changes
Shrinkage compensate for expansion eliminating the need for investment shrinkage/ expansion
Thermal processing
5000c @ 160/hr
* 16 hrs
Room temperatur
e
6500
c8 hrs*6000
c in 1 hr
13500
c stop13500
c@ 420/hr
PHYSICAL & MECHANICAL PROPERTIES
Density Range of melting &
firing temperatures Ultimate strength Modulus of elasticity Elongation & yield
strength
Hardness Tarnish & corrosion Castability-
moldability Finishing & polishing Soldering
Comparison of physical & mechanical properties
Class I: 15-16 gm/cm3
Class II: 11-12 gm/cm3
Class III: 10-11 gm/cm3
Class IV: 8 gm/cm3
Class V: 2.7 gm/cm3
Lower density: more force in centrifugal casting machine; but more restorations per unit weight
Density
Class IV- Highest melting range Class I- Lowest Class I & II: Regular gas-air fuel, calcium
sulfate dihydrate bonded investments, low heat technique
Class IV & Class III: phosphate & silicate bonded investments, acetylene-oxygen, gas-oxygen, electric resistance or induction melting
Casting environment – carefully controlled for III & IV
Range of melting & firing temperatures
Cast ceramics : Transmitted / induced heat used
Range of melting & firing temperatures
Thermoplastic:
casting Fusing: completion of thermal processing
Mechanical failure: rare Metallic alloys- far superior to cast ceramics:
Tensile & Shear- ductile/ plastic failure Ceramics: Stronger under compression-
Brittle fracture Tensile strength s from Class I to IV
Ultimate strength
Modulus of elasticity
Class V materials : 6 times as rigid as Class I
Factor in abrasion resistance
All materials: exceed enamel’s
Maximum: class V High abrasive
resistance
Hardness
Measures of forces needed to achieve deformability/ burnishability
Class I alloys: least yield strength & greatest elongation- highest deformability under the least amount of forces
Class IV alloys: needs special equipment for designing
Class V: Zero elongation & yield strength coinciding with brittle fracture
Elongation & Yield strength
Class V: Absolutely chemically inert Class I: Nobility Class IV: Passivity Class III: least resistant to corrosion greater Ag content: especially in sulfurous environment Class II: low Au content- surface &marginal
deterioration
Tarnish & Corrosion
Class II & III alloys: contraindicated – high sulfur diets and areas of stagnation of plaque & food substrates
Alloy with highest Pd content in Class II & III chosen- questionable cases
Tarnish & Corrosion
Class III & IV alloys: rough surface of castings Pd: H2 & Ag: O2 Incorporated & released during solidification-
porosities & rough surface Class II, III, IV: closed furnaces & electric
conduction melting Class I: Maximum density & good surface
detail Overcome the gas pressure within the mold
Castability-moldability
Metallic alloys: solidification shrinkage- investment expansion
Class IV alloys except the Be containing ones: reproduce least details
Modifications in cavity & tooth preps. Needed
Castability-moldability
Reproduction of wax pattern: single process with alloys & in two stages with ceramics- one done on the die
High density: ceramic can wet all the details of the mold & reproduce the pattern
No shrinkage- no expansion of investment required
Class I & II: Easiest among the alloys Class III: more time & effort required Class IV: high speed equipment, more
abrasive tools, more time compared others Cast ceramics: finished after retrieval prior to thermal processing ; glazed during & after thermal processing
Finishing & Polishing
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Class I & II: Au solders- predictable & without much failures
Class III: Ag solders
Reducing zone of the flameSolder melting temperature: 1500c lower
than mother alloyProper timing & atmosphere
Soldering
Class IV: Inert environment: Oven soldering
Specific solder: each alloyRisks: solder failure & change in composition
of mother alloy Cast ceramics: multiple attached units: cast
together Contact & contour modifications: baking on
aluminous porcelain
Plaque control Caries control Control of periodontal problems Proper foundation Control of the pulpal condition of the tooth Occlusal equilibriation Diagnostic wax-ups & temporary restoration
MOUTH PREPARATION PRIOR TO CAST RESTORATIONS
Plaque Control
Cast/ cement/ tooth structure: vulnerability
Plaque control measures
Plaque index < 10%
Rampant uncontrolled carious processes halted
Indirect pulp capping, amalgam/ composite resin restorations
Little or no evidence of recurrent decay
Caries Control
Ideal to start therapy with a sound periodontium, unless it is indicated as part of periodontal therapy & maintenance
Periodontal therapy: under control
Control of Periodontal problems
Pockets eradicated Bone resorption arrested
Defects corrected Exposed roots & crown surfaces free from deposits
Gingival tissues healed Apparent clinical crown dimensions stable
Badly broken down teeth: Substructure/ foundation
Before tooth preparation for cast restoration: the need diagnosed & implemented
Foundation building for tooth after unsuccessful attempt for cast restoration - frustrating
Proper Foundation
Proper preop evaluation of the pulp- dentin- root canal system
Extensive defects/ one or more previous restorations
Irreversible pathological changes: cast restoration procedures
Endodontic therapy- part of mouth preparation
Control of pulpal condition of the tooth
Premature occluding contacts: greater & long standing disturbances in stomatognathic system
No interfering/ premature contacts Pattern of reliable protective mechanism for
mandibular disclusion
Occlusal Equilibriation
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Full arch study models: mounted on semi or fully adjustable articulator
Involved teeth reduced & diagnostic wax-up made in the desired occlusal shape & relationship
Duplicate stone models: temporary & final restorations
Teeth roughly prepared
Diagnostic wax-ups & Temporary Restorations
Teeth roughly prepared
Restored with temporary
restorations
Worn by patient & periodically
examinedChanges made in temporaries
Utmost compatibility
between stomatognathic
system
Achieved & verified
Cast restorations fabricated
Replicas of temporaries
Physiologic & therapeutic to
stomatognathic system
References
Marzouk MA, Simonton AL, Gross RD. Operative Dentistry- Modern Theory & Practice, 1st Edition
Roberson TM, Heymann HO, Swift EJ. Sturdevant’s Art & Science of Operative Dentistry, 5th Edition
Anusavice, Shen, Rawls. Phillips’ Science of Dental Materials, 12th Edition
Summit JB, Robbins JW, Schwartz RS. Fundamentals of Operative Dentistry. A Contemporary Approach. 2nd edition
Schluein TM. Significant events in the history of Operative dentistry. Journal of History of Dentistry. Vol 53. No 2.2005.63-72
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