casting defects

DEPARTMENT OF CONSERVATIVE DENTISTRY DEPARTMENT OF CONSERVATIVE DENTISTRY AND ENDODONTICSAND ENDODONTICS

IntroductionIntroduction

The dental profession has used precision-type The dental profession has used precision-type castings for the most part of century. Using the castings for the most part of century. Using the lost wax technique, Taggart in 1907 lost wax technique, Taggart in 1907 developed a process for making castings used developed a process for making castings used in restoration of prepared teeth. Since the in restoration of prepared teeth. Since the process did not take into account all the process did not take into account all the dimensional changes associated with the dimensional changes associated with the casting technique, the resultant product did casting technique, the resultant product did exhibit some problems in terms of dimensional exhibit some problems in terms of dimensional accuracy.accuracy.

DefinitionDefinition

Casting is a fabrication process whereby a totally molten Casting is a fabrication process whereby a totally molten metal is poured into a mold cavity having a desired shape ; metal is poured into a mold cavity having a desired shape ; upon solidification, the metal assumes the shape of the upon solidification, the metal assumes the shape of the mold.mold.

Classification of Dental Casting Classification of Dental Casting AlloysAlloys

Alloy TypeAlloy Type Total noble metal contentTotal noble metal contentHigh noble metalHigh noble metal contains≥40 wt% Au and ≥60 wt% of contains≥40 wt% Au and ≥60 wt% of

the noble metal elements (Au+Ir+Osthe noble metal elements (Au+Ir+Os+Pt+Rh+Ru )+Pt+Rh+Ru )

Noble metalNoble metal Contains ≥25 wt% of the noble metal Contains ≥25 wt% of the noble metal elementselements

Predominantly base metalPredominantly base metal Contains <25 wt% of the noble metal Contains <25 wt% of the noble metal elementselements

Journal of American Dental Association (1984)Journal of American Dental Association (1984)

Classification of Alloys for All Metal Restorations , Metal Ceramic Restorations, Classification of Alloys for All Metal Restorations , Metal Ceramic Restorations, and Frameworks for Removable Partial Denturesand Frameworks for Removable Partial Dentures

Alloy TypeAlloy Type All MetalAll Metal Metal CeramicMetal Ceramic Removable Partial Removable Partial DenturesDentures

High NobleHigh Noble Au-Ag-Cu-PdAu-Ag-Cu-PdMetal Ceramic alloysMetal Ceramic alloys

Au-Pt-PdAu-Pt-PdAu-Pd-Ag(5-12 wt% Au-Pd-Ag(5-12 wt% Ag)Ag)Au-Pd (no Ag)Au-Pd (no Ag)

Au-Ag-Cu-PdAu-Ag-Cu-Pd

Noble Noble Ag-Pd-Au-CuAg-Pd-Au-CuAg-PdAg-PdMetal Ceramic alloysMetal Ceramic alloys

Pd-Au (no Ag)Pd-Au (no Ag)Pd-Au-AgPd-Au-AgPd-AgPd-AgPd-CuPd-CuPd-CoPd-CoPd-Ga-AgPd-Ga-Ag

Ag-Pd-Au-CuAg-Pd-Au-CuAg-PdAg-Pd

Base MetalBase Metal Pure TiPure TiTi-Al-VTi-Al-VNi-Cr-Mo-BeNi-Cr-Mo-BeNi-Cr-MoNi-Cr-MoCo-Cr-WCo-Cr-WAl bronzeAl bronze

Pure TiPure TiTi-Al-VTi-Al-VNi-Cr-Mo-BeNi-Cr-Mo-BeNi-Cr-MoNi-Cr-MoCo-Cr-WCo-Cr-W

Pure TiPure TiTi-Al-VTi-Al-VNi-Cr-Mo-BeNi-Cr-Mo-BeNi-Cr-MoNi-Cr-MoCo-Cr-WCo-Cr-W

Phillips’; Science of dental material ; 10Phillips’; Science of dental material ; 10 thth edition edition

Classification OfClassification Of Traditional Casting Traditional Casting AlloysAlloys

TYPETYPE HARDNESSHARDNESS USEUSE

II SoftSoft Single SurfacesSingle Surfaces

IIII MediumMedium Inlays/OnlaysInlays/Onlays

IIIIII HardHard Crowns/BridgesCrowns/Bridges

IVIV ExtraExtra Bridges & partial Bridges & partial denturesdentures

JADA, Leinfelder ;1997;128;37-45

Casting ShrinkageCasting Shrinkage Most metals & alloys, including gold & noble metal Most metals & alloys, including gold & noble metal

alloys, shrink when they change from the liquid to the alloys, shrink when they change from the liquid to the solid state.solid state.

Shrinkage occurs in 3 stages:Shrinkage occurs in 3 stages:• The thermal contraction of the liquid metal between The thermal contraction of the liquid metal between

the temperature to which it is heated and the liquidus the temperature to which it is heated and the liquidus temperature.temperature.

• The contraction of metal inherent in its change from The contraction of metal inherent in its change from liquid to the solid state.liquid to the solid state.

• The thermal contraction of the solid metal that occurs The thermal contraction of the solid metal that occurs down the room temperature.down the room temperature.

Phillips’; Science of dental material ; 10th editionPhillips’; Science of dental material ; 10th edition

COMPENSATION FOR SHRINKAGECOMPENSATION FOR SHRINKAGE

• Setting or Hygroscopic expansion of investment Setting or Hygroscopic expansion of investment material: Hygroscopic low heat techniquematerial: Hygroscopic low heat technique

• Thermal expansion of investment: High heat thermal Thermal expansion of investment: High heat thermal expansion techniqueexpansion technique

Hygroscopic low heat techniqueHygroscopic low heat technique

Obtains its compensation expansion from 3 sources:Obtains its compensation expansion from 3 sources:1.1. The 37˚C water bath expands the wax patternThe 37˚C water bath expands the wax pattern2.2. The warm water entering the investment mold from The warm water entering the investment mold from

the top adds some hygroscopic expansionthe top adds some hygroscopic expansion3.3. The thermal expansion at 500˚C provides the The thermal expansion at 500˚C provides the

needed thermal expansion.needed thermal expansion.

Because of the potential for reduced venting, back Because of the potential for reduced venting, back pressure porosity is a greater hazard in this pressure porosity is a greater hazard in this technique than the high heat technique, since the technique than the high heat technique, since the investments generally employed with this technique investments generally employed with this technique may be more dense. may be more dense.

High heat thermal ExpansionHigh heat thermal Expansion

• Obtain its compensation expansion almost Obtain its compensation expansion almost entirely by burn-out.entirely by burn-out.

• Additional expansion results from the slight Additional expansion results from the slight heating of gypsum investments on setting, thus heating of gypsum investments on setting, thus expanding the wax pattern, & the water expanding the wax pattern, & the water entering the investment from the wet liner, entering the investment from the wet liner, which adds a small amount of hygroscopic which adds a small amount of hygroscopic expansion to the normal setting expansion.expansion to the normal setting expansion.

INVESTMENT MATERIALSINVESTMENT MATERIALS Gypsum Bonded InvestmentsGypsum Bonded Investments Phosphate Bonded InvestmentsPhosphate Bonded Investments Ethyl Silicate Bonded InvestmentsEthyl Silicate Bonded Investments


Gypsum Based InvestmentsGypsum Based Investments

The gypsum based investments have traditionally been used for The gypsum based investments have traditionally been used for casting of gold alloy inlays, onlays, crowns and fixed partial casting of gold alloy inlays, onlays, crowns and fixed partial dentures.dentures.

Main ConstituentsMain Constituents:-:- a - hemihydratea - hemihydrate of gypsum and quartz of gypsum and quartz which serves as a which serves as a binderbinder and and gives strengthgives strength to the investment. to the investment.

Gypsum shrinks at a temperature range between 200 and 400˚C, Gypsum shrinks at a temperature range between 200 and 400˚C, it slightly expands between 400 and 700˚C and than it undergoes it slightly expands between 400 and 700˚C and than it undergoes significant shrinkage beyond 700˚C. Because of this property, the significant shrinkage beyond 700˚C. Because of this property, the gypsum should not be heated beyond 700˚C. In order to gypsum should not be heated beyond 700˚C. In order to compensate for this shrinkage (which could cause the pattern compensate for this shrinkage (which could cause the pattern void to expand) the pure gypsum moulds are significantly void to expand) the pure gypsum moulds are significantly undersized.undersized.

Silica is added to provide a refractory component. If silica is Silica is added to provide a refractory component. If silica is added to the investment, this shrinkage can be reduced or even added to the investment, this shrinkage can be reduced or even turned into expansion.turned into expansion.


Phosphate Bonded InvestmentsPhosphate Bonded Investments

The spread of use of phosphate based investment is caused by The spread of use of phosphate based investment is caused by

an increase in use of metal ceramic prosthesis, which require an increase in use of metal ceramic prosthesis, which require higher melting temperatures than gold alloys.higher melting temperatures than gold alloys.

The investment consists also of binders and refractory filler, The investment consists also of binders and refractory filler, which are the same as for the gypsum based investments. which are the same as for the gypsum based investments. However, the binder in this case is magnesium oxide and a However, the binder in this case is magnesium oxide and a monoammonium phosphate. Carbon is also often added to the monoammonium phosphate. Carbon is also often added to the investment in order to help to produce a clean casting and to investment in order to help to produce a clean casting and to encourage easier divesting of the casting from the mould. encourage easier divesting of the casting from the mould. Differently to the gypsum based investments, these investment Differently to the gypsum based investments, these investment in practice do not show signs of setting shrinkage, but rather of in practice do not show signs of setting shrinkage, but rather of slight expansion.slight expansion.


Ethyl Silicate Bonded InvestmentsEthyl Silicate Bonded Investments• Used in construction of high-fusing base metal Used in construction of high-fusing base metal

partial denture alloys.partial denture alloys.• Binder is Silica gel which reverts to silica on Binder is Silica gel which reverts to silica on

heating.heating.• This type of investment can be heated to This type of investment can be heated to

10901090˚C -1180˚C & is compatible with higher ˚C -1180˚C & is compatible with higher fusing alloys.fusing alloys.

CASTING- LOST WAX CASTING- LOST WAX PROCEDUREPROCEDURE

The process involves producing a metal casting using a refractory mould made from a wax replica pattern.

The steps involved in the process or the lost wax casting are:· Create a wax pattern of the missing tooth / rim· Sprue the wax pattern· Invest the wax pattern· Eliminate the wax pattern by burning it (inside the furnace or

in hot water) .This will create a mould.· Force molten metal into the mould - casting.· Clean the cast.· Remove sprue from the cast· Finish and polish the casting on the die.

::SPRUE:SPRUE: A sprue is the channel in a refractory investment mold A sprue is the channel in a refractory investment mold

through which molten metal flows.through which molten metal flows.

Figure 1 – Spherical reservoir on the vertical sprue (left), indirect sprue with the horizontal reservoir bar

Sprue

Lost - Head(Reservoir)

For preventing cavities and

porosities, due to thermal contraction

LINER:LINER: Investment materials have a property of expanding on

setting.If the investment was confined on the outside this could cause shrinkage of the of the mould / wax pattern.

In order to prevent this effect a flexible split ring or a rubber ring could be used.

However, the most commonly used technique is to line the casting ring with either an aluminosilicate liner or a cellulose liner.

The molten mass

Hot zoneCrucible(melting pot)

Casting mold

CASTING THE DENTAL ALLOYCASTING THE DENTAL ALLOY

CASTING MACHINESCASTING MACHINES1.1. Centrifugal Casting MachineCentrifugal Casting Machine

2.2. Electrical Electrical Resistance- Resistance- Heated Casting Heated Casting MachineMachine

3.3. Induction Melting Induction Melting MachineMachine

Melting Noble Metal Alloys:Melting Noble Metal Alloys:

There are several methods for melting of There are several methods for melting of alloys, which are combined with the castingalloys, which are combined with the casting

methods and appropriate casting machines.:methods and appropriate casting machines.:· Torch melting,· Torch melting,· Electrical melting.· Electrical melting.

Cleaning the cast:

. The dark surface of the casting can be removed by a The dark surface of the casting can be removed by a process called pickling – heating the discoloured process called pickling – heating the discoloured casting in an acid until the discoloration vanishes.casting in an acid until the discoloration vanishes.

. Polishing of the casting is the final in its preparation. . Polishing of the casting is the final in its preparation. Rubber, rag or felt wheels impregnated with abrasivesRubber, rag or felt wheels impregnated with abrasives

are used in the initial phase of this stage. Final are used in the initial phase of this stage. Final polishing is achieved using various oxides of tin and polishing is achieved using various oxides of tin and aluminium used in conjunction with a small rag or aluminium used in conjunction with a small rag or chamois buffing wheel, followed with an iron oxide chamois buffing wheel, followed with an iron oxide rouge.rouge.

CASTING DEFECTSCASTING DEFECTSDefects in casting can be classified as:Defects in casting can be classified as:1.1. DISTORTIONDISTORTION2.2. SURFACE ROUGHNESS & SURFACE ROUGHNESS &

IRREGULARITIESIRREGULARITIES3.3. POROSITYPOROSITY4.4. DISCOLOURATIONDISCOLOURATION5.5. INCOMPLETE CASTING OR MISSING INCOMPLETE CASTING OR MISSING

DETAILDETAIL

Distortion:Distortion:Causes-Causes-• Distortion of wax patternDistortion of wax pattern• Due to uneven movement of the walls of wax pattern Due to uneven movement of the walls of wax pattern

when investment is setting. The gingival margins are when investment is setting. The gingival margins are forced apart by the mold expansion, whereas the forced apart by the mold expansion, whereas the solid occlusal bar of wax resists expansion during the solid occlusal bar of wax resists expansion during the early stage of setting.early stage of setting.

Solutions-Solutions-• Proper manipulation of wax & handling of the Proper manipulation of wax & handling of the

pattern.pattern.

Poor Surface finish:Poor Surface finish:Causes-Causes-• Air bubbles on the patternAir bubbles on the pattern• Water films causing ridges & veins on the surface.Water films causing ridges & veins on the surface.• Too rapid heating resulting in fins or spinesToo rapid heating resulting in fins or spines• Underheating causing incomplete elimination of waxUnderheating causing incomplete elimination of wax• Inappropriate water/powder ratioInappropriate water/powder ratio• Prolonged heatingProlonged heating• Temperature of alloy too highTemperature of alloy too high• Casting pressure too highCasting pressure too high• Foreign bodiesForeign bodies• Impact of molten alloyImpact of molten alloy• Pattern positionPattern position

Solutions-Solutions-• Use of Vacuum Investing TechniqueUse of Vacuum Investing Technique• Vibrate before & after mixingVibrate before & after mixing• Use a wetting agent to reduce surface tension of wax pattern.Use a wetting agent to reduce surface tension of wax pattern.• Air dry the wetting agent as excess water will dilute Air dry the wetting agent as excess water will dilute

investment, causing irregularitiesinvestment, causing irregularities• The mold should be heated graduallyThe mold should be heated gradually• Heat the ring for sufficient period of time so that the Heat the ring for sufficient period of time so that the

carbonaceous residue is removedcarbonaceous residue is removed• Water/powder ratio should be accurateWater/powder ratio should be accurate• Gypsum bonded investments should never be heated above Gypsum bonded investments should never be heated above

700˚C700˚C• Alloys submitted to vacuum casting showed decreased surface Alloys submitted to vacuum casting showed decreased surface

roughness, compared to alloys submitted to acetylene- oxygen roughness, compared to alloys submitted to acetylene- oxygen flame casting.flame casting. Journal of Prosthetic dentistry, 2004, vol 92, 274-277Journal of Prosthetic dentistry, 2004, vol 92, 274-277

Porosity:Porosity:

Porosity of the casting can be spread within the Porosity of the casting can be spread within the casting and on its surface. The surface porosity casting and on its surface. The surface porosity adds to surface roughness, but can also be a adds to surface roughness, but can also be a sing of the internal porosity. The internal sing of the internal porosity. The internal porosity could weaken the casting, may cause porosity could weaken the casting, may cause discoloration if spread to the surface and in discoloration if spread to the surface and in extreme cases could lead to a leakage.extreme cases could lead to a leakage.

Classification of porosities (According to Phillips’):Classification of porosities (According to Phillips’):

PorositiesPorosities

Solidification Solidification DefectsDefects

Trapped gasesTrapped gases Residual AirResidual Air

Localized Localized ShrinkageShrinkage

MicroporosityMicroporosity PinholePinhole PorosityPorosity

Gas Gas InclusionsInclusions

SubsurfaceSubsurface PorosityPorosity


Localized Shrinkage PorosityLocalized Shrinkage Porosity

Causes:Causes: Generally caused by incomplete feeding of molten Generally caused by incomplete feeding of molten

metal during solidificationmetal during solidification..If the sprue is not properly If the sprue is not properly designed and implemented then it may solidify before designed and implemented then it may solidify before the feeding is complete thus preventing a continuous the feeding is complete thus preventing a continuous supply of molten alloy. This type of defect usually supply of molten alloy. This type of defect usually occurs close to the occurs close to the sprue-casting junction.sprue-casting junction.

Solutions:Solutions: Ryge et al recommended the use of a sprue diameter Ryge et al recommended the use of a sprue diameter

larger than the thickest cross section of the casting.larger than the thickest cross section of the casting.

Journal of dental rest.; Jan 1981; vol 60; no1; page 59-67Journal of dental rest.; Jan 1981; vol 60; no1; page 59-67Phillips’; science of dental materials; 10th editionPhillips’; science of dental materials; 10th edition

Macroporosity:Macroporosity: Causes-Causes-• Primarily a shrinkage porosityPrimarily a shrinkage porosity• The portion of a cylindrical casting which solidifies The portion of a cylindrical casting which solidifies

last is the low pressure side of the liquid metal close last is the low pressure side of the liquid metal close to the free surface of the button, therefore to the free surface of the button, therefore macroporosity always appears in this portion of macroporosity always appears in this portion of casting.casting.

Solution-Solution-• Reduce by providing a reservoir contiguous or close Reduce by providing a reservoir contiguous or close

to the low pressure end of the liquid metalto the low pressure end of the liquid metal• It may be affected by the closeness of the individual It may be affected by the closeness of the individual

units in a multiple unit casting.units in a multiple unit casting.


Journal of dental restoration; Jan 1981;vol 60; no. 1;page 59-67Journal of dental restoration; Jan 1981;vol 60; no. 1;page 59-67

HOT SPOT:-HOT SPOT:- Localized shrinkage porosity may result from Localized shrinkage porosity may result from

the formation of HOT SPOT when metal the formation of HOT SPOT when metal impinges on the mold surface so that here the impinges on the mold surface so that here the metal remains molten while it solidifies metal remains molten while it solidifies everywhere else. This hot spot causes the local everywhere else. This hot spot causes the local region to freeze last and result in region to freeze last and result in SUCK BACK SUCK BACK POROSITY.POROSITY.

Solutions:Solutions: Flare the point of sprue attachmentFlare the point of sprue attachment Proper placement of sprueProper placement of sprue Do not use excessively long sprueDo not use excessively long sprue Use a reservoirUse a reservoir Reduce the mold-melt temperature differential Reduce the mold-melt temperature differential

(i.e. lower the casting temperature by about (i.e. lower the casting temperature by about 30˚C).30˚C).

Microporosity:Microporosity:

Microporosity is also caused by solidification Microporosity is also caused by solidification shrinkage, but generally happens in fine grain shrinkage, but generally happens in fine grain alloys when the solidification is too rapid for alloys when the solidification is too rapid for the microvoids to segregate. This in turn is the microvoids to segregate. This in turn is caused the mould or casting temperature being caused the mould or casting temperature being too low.too low.

Trapped GasesTrapped Gases 1.1. Pinhole PorosityPinhole Porosity2.2. Gas Inclusion PorosityGas Inclusion Porosity

• Both these porosities are related to the Both these porosities are related to the entrapment of gas during solidification.entrapment of gas during solidification.

• Both are characterized by a spherical Both are characterized by a spherical contour.contour.

• Gas inclusion porosities are much higher Gas inclusion porosities are much higher than pinhole porosities.than pinhole porosities.

SUBSURFACE POROSITYSUBSURFACE POROSITYCause-Cause- Simultaneous nucleation of solid grains and gas bubbles at the first Simultaneous nucleation of solid grains and gas bubbles at the first

moment that the metal freezes at the mold wallsmoment that the metal freezes at the mold walls

Solution-Solution-• Diminished by controlling the rate at which the molten metal enters the Diminished by controlling the rate at which the molten metal enters the

mold mold • Ryge et al reported that subsurface & microporosities are reduced by Ryge et al reported that subsurface & microporosities are reduced by

the use of a sufficiently long sprue & a melt temperature of 100˚C-the use of a sufficiently long sprue & a melt temperature of 100˚C-150˚C above the melting point of alloy.150˚C above the melting point of alloy.

• According to Leinfelder et al reported that long sprues are preferable According to Leinfelder et al reported that long sprues are preferable for thick castings while short sprues are beneficial for thin castings i.e. for thick castings while short sprues are beneficial for thin castings i.e. the sprue design should be related to the surface area-to-volume ratio of the sprue design should be related to the surface area-to-volume ratio of castings.castings.

Journal of dental rest.; Jan 1981; vol 60; no1; page 59-67Journal of dental rest.; Jan 1981; vol 60; no1; page 59-67Phillips’; science of dental materials; 10Phillips’; science of dental materials; 10 thth edition edition

ENTRAPPED AIR POROSITYENTRAPPED AIR POROSITY• Referred to as Referred to as Back Pressure porosity.Back Pressure porosity.• Can produce large concave depression.Can produce large concave depression.Causes-Causes- Inability of the air in the mold to escape through the Inability of the air in the mold to escape through the

pores in the investment or by the pressure gradient pores in the investment or by the pressure gradient that displaces the air pocket toward the end of the that displaces the air pocket toward the end of the investment via the molten sprue & button.investment via the molten sprue & button.

Journal of dental rest.; Jan 1981; vol 60; no1; page 59-67Journal of dental rest.; Jan 1981; vol 60; no1; page 59-67Phillips’; science of dental materials; 10Phillips’; science of dental materials; 10 thth edition edition

Solution-Solution-• Proper burnoutProper burnout• An adequate mold & casting temperature.An adequate mold & casting temperature.• A sufficiently high casting pressureA sufficiently high casting pressure• Proper liquid : powder ratio.Proper liquid : powder ratio.• The thickness of investment between the tip of the pattern and The thickness of investment between the tip of the pattern and

the end of the ring should not be greater than 6mm.the end of the ring should not be greater than 6mm.• Srickland & Sturdevant suggested that sprue design variables Srickland & Sturdevant suggested that sprue design variables

have no effect on these porosities; venting, high melt have no effect on these porosities; venting, high melt temperatures, proper positioning of the pattern in the ring, temperatures, proper positioning of the pattern in the ring, choice of investment & the use of reservoir can assist in choice of investment & the use of reservoir can assist in reducing or eliminating the back pressure porosities. reducing or eliminating the back pressure porosities.

Journal of dental rest.; Jan 1981; vol 60; no1; page 59-67Journal of dental rest.; Jan 1981; vol 60; no1; page 59-67• Phillips’; science of dental materials; 10th editionPhillips’; science of dental materials; 10th edition

INCOMPLETE CASTINGSINCOMPLETE CASTINGS

Causes-Causes-• Inadequate spruing ( sprue former too small)Inadequate spruing ( sprue former too small)• Alloy not hot enoughAlloy not hot enough• Incomplete elimination of wax residues from the moldIncomplete elimination of wax residues from the mold• Mold too coldMold too cold• Ingate obstructedIngate obstructed• Insufficient casting forceInsufficient casting force

Solutions-Solutions-• Use proper size of sprue formerUse proper size of sprue former• Casting temperature should be higher than the Casting temperature should be higher than the

liquidus temperature of alloy liquidus temperature of alloy • Ensure that no debris blocks the ingateEnsure that no debris blocks the ingate• Use adequate amount of force for castingUse adequate amount of force for casting

DISCOLOURATIONDISCOLOURATIONCauses-Causes-• Sulphur contamination of casting causing black Sulphur contamination of casting causing black

castingscastings• Contamination with copper during picklingContamination with copper during pickling• Contamination with mercuryContamination with mercurySolution-Solution-• Avoid overheating of investment Avoid overheating of investment • Avoid use of torch flame as it contains sulphurAvoid use of torch flame as it contains sulphur• Avoid use of steel tongs to hold casting during Avoid use of steel tongs to hold casting during

picklingpickling• Castings should never be placed with amalgam dies Castings should never be placed with amalgam dies

or kept on a table where amalgam scrap is presentor kept on a table where amalgam scrap is present

ReferencesReferences

• Phillips’; Science of dental materials; 10Phillips’; Science of dental materials; 10thth edition. edition.• Journal of American Dental AssociationJournal of American Dental Association, ,

Leinfelder ;1997Leinfelder ;1997• Journal of American Dental Association: 1984Journal of American Dental Association: 1984• Journal of Dental Restoration; Jan 1981; vol 60Journal of Dental Restoration; Jan 1981; vol 60• Journal of American Dental Association; 1993Journal of American Dental Association; 1993• Journal of Prosthetic Dentistry; 1989Journal of Prosthetic Dentistry; 1989• Journal of Prosthetic Dentistry; 2004Journal of Prosthetic Dentistry; 2004

casting defects

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