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

Thank you!!