Casting defects/ dentist laboratory

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Casting defects/ dentist laboratory

  1. 1. Casting defectsCasting defects INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.comwww.indiandentalacademy.com
  2. 2. ContentsContents • INTRODUCTIONINTRODUCTION • 2 CLASSIFICATION OF DEFECTS-2 CLASSIFICATION OF DEFECTS- • A) Defects in the wax patternA) Defects in the wax pattern • B) Defects in the investing procedureB) Defects in the investing procedure • C) Problems in burnout procedureC) Problems in burnout procedure • D) Problems during casting procedureD) Problems during casting procedure www.indiandentalacademy.comwww.indiandentalacademy.com
  3. 3. • CLASSIFICATION OF DEFECTSCLASSIFICATION OF DEFECTS (ANUSAVICE)(ANUSAVICE) • CLASSIFICATION OF DEFECT ( RUDDCLASSIFICATION OF DEFECT ( RUDD AND MORROW)AND MORROW) • CONCLUSIONCONCLUSION • REFERENCESREFERENCES www.indiandentalacademy.comwww.indiandentalacademy.com
  4. 4. IntroductionIntroduction • In dentistry the lost-wax casting technic was notIn dentistry the lost-wax casting technic was not popular until 1907 when W.H. Taggart intro­popular until 1907 when W.H. Taggart intro­ duced his technic and casting machine. Todayduced his technic and casting machine. Today the lost-wax technic is common practice and isthe lost-wax technic is common practice and is used for a variety of casting operationsused for a variety of casting operations • The casting method consists of forming a waxThe casting method consists of forming a wax pattern, surrounding it with investment material,pattern, surrounding it with investment material, and later heating the investment mold to removeand later heating the investment mold to remove the wax before casting the molten metal into thethe wax before casting the molten metal into the moldmold www.indiandentalacademy.comwww.indiandentalacademy.com
  5. 5. • Defects in Wax PatternDefects in Wax Pattern • 1. Distortion1. Distortion • 2. Surface roughness and irregularities2. Surface roughness and irregularities • 3. Air bubbles3. Air bubbles • 4. Water film4. Water film www.indiandentalacademy.comwww.indiandentalacademy.com
  6. 6. Defects in Burn out ProcedureDefects in Burn out Procedure • 1. Rapid Heating Rates1. Rapid Heating Rates • 2. Under heating2. Under heating • 3. Prolonged heating3. Prolonged heating www.indiandentalacademy.comwww.indiandentalacademy.com
  7. 7. • Rough surface on castingRough surface on casting • Due to prolonged overheating of gypsumDue to prolonged overheating of gypsum bonded investment.bonded investment. • Prevention- use correct heating cycle forPrevention- use correct heating cycle for burnout procedure. Do not heat aboveburnout procedure. Do not heat above 1290F (700C)1290F (700C) www.indiandentalacademy.comwww.indiandentalacademy.com
  8. 8. • Problems DURING CASTINGProblems DURING CASTING PROCEDUREPROCEDURE 1.1. Incomplete castingsIncomplete castings Alloy not hot enoughAlloy not hot enough • Have casting temperature above indicatedHave casting temperature above indicated fusion temperature of alloyfusion temperature of alloy • Mold too coldMold too cold • Oven too cold- check pyrometer; mould shouldOven too cold- check pyrometer; mould should heat soak 1 hour at burnout temperature.heat soak 1 hour at burnout temperature. www.indiandentalacademy.comwww.indiandentalacademy.com
  9. 9. --Insufficient casting forceInsufficient casting force • Force alloy into the mold rapidly;useForce alloy into the mold rapidly;use centrifugal machine with good springs andcentrifugal machine with good springs and several winds.Use air pressure andseveral winds.Use air pressure and vacuum machines with proper force.vacuum machines with proper force. • --Insufficient goldInsufficient gold • Cast enough gold to allow for goodCast enough gold to allow for good www.indiandentalacademy.comwww.indiandentalacademy.com
  10. 10. • 2. Rough Surface on casting2. Rough Surface on casting • Due to -Too much casting pressure causingDue to -Too much casting pressure causing investment breakdown from force of alloy.investment breakdown from force of alloy. • Elimination-Elimination- • Do not wind machine too tightly.Do not wind machine too tightly. • A gauge pressure of .10 to.14MPa in an airA gauge pressure of .10 to.14MPa in an air pressure casting machinepressure casting machine • Three to four turns of the spring in an averageThree to four turns of the spring in an average type of centrifugal casting machines is sufficienttype of centrifugal casting machines is sufficient for small castingsfor small castings www.indiandentalacademy.comwww.indiandentalacademy.com
  11. 11. Classification of casting defectsClassification of casting defects (ANUSAVICE)(ANUSAVICE) • Defects in castings can be classifiedDefects in castings can be classified under four headings:under four headings: • (1) Distortion;(1) Distortion; • (2) Sur­face roughness and irregularities;(2) Sur­face roughness and irregularities; • (3) Porosity;(3) Porosity; • (4) Incomplete or missing detail(4) Incomplete or missing detail www.indiandentalacademy.comwww.indiandentalacademy.com
  12. 12. • DistortionDistortion • Any marked distortion of the casting isAny marked distortion of the casting is probably related to a distortion of the waxprobably related to a distortion of the wax pattern.pattern. • This type of distortion can be minimized orThis type of distortion can be minimized or prevented by proper manipulation of theprevented by proper manipulation of the wax and handling of the pattern.wax and handling of the pattern. www.indiandentalacademy.comwww.indiandentalacademy.com
  13. 13. • Some distortion of the wax pattern occursSome distortion of the wax pattern occurs as the investment hardens around it.as the investment hardens around it. • The setting and hygroscopic expansionsThe setting and hygroscopic expansions of the investment may produce aof the investment may produce a nonuniform expansion of the walls of thenonuniform expansion of the walls of the pattern.pattern. www.indiandentalacademy.comwww.indiandentalacademy.com
  14. 14. • This type of distortion occurs in part fromThis type of distortion occurs in part from the nonuniform outward movement of thethe nonuniform outward movement of the proximal walls, the gingival margins areproximal walls, the gingival margins are forced apart by the mold expansion,forced apart by the mold expansion, whereas the solid occlusal bar of waxwhereas the solid occlusal bar of wax resists expansion during the early stagesresists expansion during the early stages of settingof setting www.indiandentalacademy.comwww.indiandentalacademy.com
  15. 15. • The configuration of the pattern, the typeThe configuration of the pattern, the type of wax, and the thickness influence theof wax, and the thickness influence the distortion that occurs.distortion that occurs. • Distortion increases as the thickness ofDistortion increases as the thickness of the pattern decreases.the pattern decreases. • The less the setting expansion of theThe less the setting expansion of the investment, the less the distortion.investment, the less the distortion. www.indiandentalacademy.comwww.indiandentalacademy.com
  16. 16. Surface Roughness, Irregularities,Surface Roughness, Irregularities, and Discolorationand Discoloration • The surface of a dental casting should beThe surface of a dental casting should be an accurate reproduction of the waxan accurate reproduction of the wax pattern from which it is made.pattern from which it is made. • Excessive roughness or irregularities onExcessive roughness or irregularities on outer surface of the casting necessitateouter surface of the casting necessitate additional finishing and polishing, whereasadditional finishing and polishing, whereas irregularities on the cavity surface preventirregularities on the cavity surface prevent a proper seating of an otherwise accuratea proper seating of an otherwise accurate casting.casting. www.indiandentalacademy.comwww.indiandentalacademy.com
  17. 17. • Surface roughness is defined as relativelySurface roughness is defined as relatively finely spaced surface imperfections whosefinely spaced surface imperfections whose height, width, and direction establish theheight, width, and direction establish the predominant surface pattern.predominant surface pattern. • Surface irregularities are isolatedSurface irregularities are isolated imperfections, such as nodules, that areimperfections, such as nodules, that are not characteristic of the entire surfacenot characteristic of the entire surface area.area. www.indiandentalacademy.comwww.indiandentalacademy.com
  18. 18. • The surface roughness of the dentalThe surface roughness of the dental casting is invariably somewhat greatercasting is invariably somewhat greater than that of the wax pattern from which itthan that of the wax pattern from which it is made.is made. • The difference is probably related to theThe difference is probably related to the particle size of the investment and itsparticle size of the investment and its ability to reproduce the wax pattern inability to reproduce the wax pattern in microscopic detail.microscopic detail. www.indiandentalacademy.comwww.indiandentalacademy.com
  19. 19. • Surface irregularities on an experimental casting caused by air bubbles (A),water film (B), and inclusion of foreign bodies(C). www.indiandentalacademy.comwww.indiandentalacademy.com
  20. 20. Air BubblesAir Bubbles • Small nodules on a casting are caused bySmall nodules on a casting are caused by air bubbles that become attached to theair bubbles that become attached to the pattern during or subsequent to thepattern during or subsequent to the investing procedure.investing procedure. • The best method to avoid air bubbles isThe best method to avoid air bubbles is to use the vacuum investing technique.to use the vacuum investing technique. www.indiandentalacademy.comwww.indiandentalacademy.com
  21. 21. • If a manual method is used, various precautions can beIf a manual method is used, various precautions can be observed from the investment mix before the investing.observed from the investment mix before the investing. • The use of a mechanical mixer with vibration both beforeThe use of a mechanical mixer with vibration both before and after mixing should be practiced routinely.and after mixing should be practiced routinely. • Wetting agentWetting agent ;; • A wetting agent may be helpful in preventing theA wetting agent may be helpful in preventing the collection of air bubbles on the surface of the pattern.collection of air bubbles on the surface of the pattern. • The wetting agent be applied in a thin layer.The wetting agent be applied in a thin layer. • Air-dry the wetting agent, because any excess liquidAir-dry the wetting agent, because any excess liquid dilutes the investment, possi­bly producing surfacedilutes the investment, possi­bly producing surface irregularities on the casting.irregularities on the casting. www.indiandentalacademy.comwww.indiandentalacademy.com
  22. 22. • Water FilmsWater Films • Wax is repellent to water, and if theWax is repellent to water, and if the investment becomes separated from theinvestment becomes separated from the wax pat­tern in some manner, a water filmwax pat­tern in some manner, a water film may form irregularly over the surface.may form irregularly over the surface. • Occasionally, this type of surfaceOccasionally, this type of surface irregularity appears as minute ridges orirregularity appears as minute ridges or veins on the surfaceveins on the surface www.indiandentalacademy.comwww.indiandentalacademy.com
  23. 23. • If the pattern is slightly moved, jarred, orIf the pattern is slightly moved, jarred, or vibrated after investing, or if the paintingvibrated after investing, or if the painting procedure does not result in an intimate contactprocedure does not result in an intimate contact of the investment with the pattern, such aof the investment with the pattern, such a condition may result.condition may result. • A wetting agent is of aid in the prevention ofA wetting agent is of aid in the prevention of such irregularities. Too high a L/P ratio may alsosuch irregularities. Too high a L/P ratio may also produce these surface irregularities.produce these surface irregularities. www.indiandentalacademy.comwww.indiandentalacademy.com
  24. 24. • Rapid HeatingRapid Heating • May result in fins or spines on the casting.May result in fins or spines on the casting. • Also, a characteristic surface roughnessAlso, a characteristic surface roughness may be evident because of flaking of themay be evident because of flaking of the investment when the water or steam poursinvestment when the water or steam pours into the mold. Furthermore, such a surgeinto the mold. Furthermore, such a surge of steam or water may carry some of theof steam or water may carry some of the salts used as modifiers into the mold, andsalts used as modifiers into the mold, and these salts are left as deposits on thethese salts are left as deposits on the walls after the water evaporates.walls after the water evaporates. www.indiandentalacademy.comwww.indiandentalacademy.com
  25. 25. • . The mold should be heated gradually; at. The mold should be heated gradually; at least 60 min should elapse during theleast 60 min should elapse during the heating of the investment-filled ring fromheating of the investment-filled ring from room temperature to 700° C.room temperature to 700° C. • The greater the bulk of the investment, theThe greater the bulk of the investment, the more slowly it should be heated.more slowly it should be heated. www.indiandentalacademy.comwww.indiandentalacademy.com
  26. 26. • UnderheatingUnderheating • Incomplete elimination of wax residues mayIncomplete elimination of wax residues may occur if the heating time is too short or ifoccur if the heating time is too short or if insufficient air is available in the furnace. Theseinsufficient air is available in the furnace. These factors are particularly important with the low-factors are particularly important with the low- temperature investment techniques.temperature investment techniques. • Voids or porosity may occur in the casting fromVoids or porosity may occur in the casting from the gases formed when the hot alloy comes inthe gases formed when the hot alloy comes in contact with carbon residues. Occasionally, thecontact with carbon residues. Occasionally, the casting may be covered with a tenacious carbon,casting may be covered with a tenacious carbon, coating that is virtually impossible to remove bycoating that is virtually impossible to remove by pickling.pickling. www.indiandentalacademy.comwww.indiandentalacademy.com
  27. 27. • Liquid/Powder RatioLiquid/Powder Ratio • The amount of water and investment shouldThe amount of water and investment should be measured accurately.be measured accurately. • The higher the L/P ratio, the rougher theThe higher the L/P ratio, the rougher the casting. However, if too little water is used, thecasting. However, if too little water is used, the investment may be unmanageably thick andinvestment may be unmanageably thick and cannot be properly applied to the pattern.cannot be properly applied to the pattern. • In vacuum investing, the air may not beIn vacuum investing, the air may not be sufficiently removed. In either instance, a rough ­sufficiently removed. In either instance, a rough ­ surface on the casting may result.surface on the casting may result. www.indiandentalacademy.comwww.indiandentalacademy.com
  28. 28. • Prolonged HeatingProlonged Heating • When the high-heat casting technique is used, aWhen the high-heat casting technique is used, a prolonged heating of the mold at the castingprolonged heating of the mold at the casting temperature is likely to cause a disintegration oftemperature is likely to cause a disintegration of the gypsum-bonded investment, and the walls ofthe gypsum-bonded investment, and the walls of the mold are roughened as a result.the mold are roughened as a result. Furthermore, products of decomposition areFurthermore, products of decomposition are sulfur compounds that may contaminate thesulfur compounds that may contaminate the alloy to the extent that the surface texture isalloy to the extent that the surface texture is affectedaffected www.indiandentalacademy.comwww.indiandentalacademy.com
  29. 29. • . Such contamination may be the reason. Such contamination may be the reason that the surface of the casting sometimesthat the surface of the casting sometimes does not respond to pickling.does not respond to pickling. • When the thermal expansion technique isWhen the thermal expansion technique is employed, the mold should be heated toemployed, the mold should be heated to the casting temperature—never higher—the casting temperature—never higher— and the casting should be madeand the casting should be made immediately.immediately. www.indiandentalacademy.comwww.indiandentalacademy.com
  30. 30. • Temperature of the AlloyTemperature of the Alloy • If an alloy is heated to too high a temperatureIf an alloy is heated to too high a temperature before casting, the surface investment is likely tobefore casting, the surface investment is likely to be attacked, and a surface roughness maybe attacked, and a surface roughness may result.result. • In all probability, the alloy will not be overheatedIn all probability, the alloy will not be overheated with a gas-air torch when used with the gaswith a gas-air torch when used with the gas supplied in most localities.supplied in most localities. • If oil is used, special care should be observedIf oil is used, special care should be observed that the color emitted by the molten alloy, forthat the color emitted by the molten alloy, for example, is no lighter than a light orange.example, is no lighter than a light orange. www.indiandentalacademy.comwww.indiandentalacademy.com
  31. 31. • Casting PressureCasting Pressure • Too high a pressure during casting canToo high a pressure during casting can produce a rough surface on the casting.produce a rough surface on the casting. • A gauge pressure of 0.10 to 0.14 MPa inA gauge pressure of 0.10 to 0.14 MPa in an air pressure casting machine or threean air pressure casting machine or three to four turns of the spring in an averageto four turns of the spring in an average type of centrifugal casting machine istype of centrifugal casting machine is sufficient for small castings.sufficient for small castings. www.indiandentalacademy.comwww.indiandentalacademy.com
  32. 32. • Composition of the InvestmentComposition of the Investment • The ratio of the binder to the quartzThe ratio of the binder to the quartz influences the surface texture of theinfluences the surface texture of the casting.casting. • A coarse silica causes a surfaceA coarse silica causes a surface roughness.roughness. • If the investment meets ANSI/ ADAIf the investment meets ANSI/ ADA Specification No. 2, the composition is notSpecification No. 2, the composition is not a factor in surface roughnessa factor in surface roughness www.indiandentalacademy.comwww.indiandentalacademy.com
  33. 33. • Foreign BodiesForeign Bodies • When foreign substances get into the mold, aWhen foreign substances get into the mold, a surface roughness may be produced.surface roughness may be produced. • For example, a rough crucible former withFor example, a rough crucible former with investment clinging to it may roughen theinvestment clinging to it may roughen the investment on its removal so that bits ofinvestment on its removal so that bits of investment are carried into the mold with theinvestment are carried into the mold with the molten alloy.molten alloy. • Carelessness in the removal of the sprue formerCarelessness in the removal of the sprue former may also be a cause.may also be a cause. www.indiandentalacademy.comwww.indiandentalacademy.com
  34. 34. • Usually, contamination results not only inUsually, contamination results not only in surface roughness but also in incom­plete areassurface roughness but also in incom­plete areas or surface voids.or surface voids. • Any casting that shows sharp, well-definedAny casting that shows sharp, well-defined deficiencies indicates the presence of somedeficiencies indicates the presence of some foreign particles in the mold, such as pieces offoreign particles in the mold, such as pieces of investment and bits of carbon from a flux.investment and bits of carbon from a flux. • Bright-appearing concavities may be the resultBright-appearing concavities may be the result of flux being carried into the mold with the metal.of flux being carried into the mold with the metal. www.indiandentalacademy.comwww.indiandentalacademy.com
  35. 35. • Surface discoloration and roughness canSurface discoloration and roughness can result from sulfur contamination, eitherresult from sulfur contamination, either from investment breakdown at elevatedfrom investment breakdown at elevated temperatures or from a high sulfur contenttemperatures or from a high sulfur content of the torch flame. The interaction of theof the torch flame. The interaction of the molten alloy with sulfur produces a blackmolten alloy with sulfur produces a black or grey layer on the surface of gold alloysor grey layer on the surface of gold alloys that is brittle and does not clean readilythat is brittle and does not clean readily during pickling.during pickling. www.indiandentalacademy.comwww.indiandentalacademy.com
  36. 36. • Impact of Molten AlloyImpact of Molten Alloy • The direction of the sprue former should be suchThe direction of the sprue former should be such that the molten gold alloy does not strike a weakthat the molten gold alloy does not strike a weak portion of the mold surface.portion of the mold surface. • Occasionally, the molten alloy may fracture orOccasionally, the molten alloy may fracture or abrade the mold surface on impact, regardlessabrade the mold surface on impact, regardless of its bulk.of its bulk. • It is unfortu­nate that sometimes the abradedIt is unfortu­nate that sometimes the abraded area is smooth so that it cannot be detected onarea is smooth so that it cannot be detected on the surface of the castingthe surface of the casting www.indiandentalacademy.comwww.indiandentalacademy.com
  37. 37. • Such a depression in the mold is reflectedSuch a depression in the mold is reflected as a raised area on the casting, often tooas a raised area on the casting, often too slight to be noticed yet sufficiently large toslight to be noticed yet sufficiently large to prevent complete seating of the casting.prevent complete seating of the casting. This type of surface roughness orThis type of surface roughness or irregularity can be avoided by properirregularity can be avoided by proper spruing so as to prevent the direct impactspruing so as to prevent the direct impact of the molten metal at an angle of 90of the molten metal at an angle of 90 degrees to the investment surface.degrees to the investment surface. www.indiandentalacademy.comwww.indiandentalacademy.com
  38. 38. • Pattern PositionPattern Position • If several patterns are invested in the same ring,If several patterns are invested in the same ring, they should not be placed too close together.they should not be placed too close together. Likewise, positioning too many patterns in theLikewise, positioning too many patterns in the same plane in the mold should be avoided. Thesame plane in the mold should be avoided. The expansion of wax is much greater than that ofexpansion of wax is much greater than that of the invest­ment, causing breakdown or crackingthe invest­ment, causing breakdown or cracking of the investment if the spacing between pat­of the investment if the spacing between pat­ terns is less than 3 mm.terns is less than 3 mm. www.indiandentalacademy.comwww.indiandentalacademy.com
  39. 39. • Carbon InclusionsCarbon Inclusions • Carbon, as from a crucible, an improperlyCarbon, as from a crucible, an improperly adjusted torch, or a carbon-containingadjusted torch, or a carbon-containing investment, can be absorbed by the alloyinvestment, can be absorbed by the alloy during casting. These particles may leadduring casting. These particles may lead to the formation of carbides or even createto the formation of carbides or even create visible carbon inclusions.visible carbon inclusions. www.indiandentalacademy.comwww.indiandentalacademy.com
  40. 40. • Other CausesOther Causes • Certain surface discolorations and roughnessCertain surface discolorations and roughness may not be evident when the casting ismay not be evident when the casting is completed but may appear during service. Forcompleted but may appear during service. For example, various gold alloys, such as solders,example, various gold alloys, such as solders, bits of wire, and mixtures of different castingbits of wire, and mixtures of different casting alloys should never be melted together andalloys should never be melted together and reused. Discoloration and corrosion may alsoreused. Discoloration and corrosion may also occur.occur. www.indiandentalacademy.comwww.indiandentalacademy.com
  41. 41. • A source of discoloration often overlooked is theA source of discoloration often overlooked is the surface contamination of a gold alloy restorationsurface contamination of a gold alloy restoration by mercury. Mercury penetrates rapidly into theby mercury. Mercury penetrates rapidly into the alloy and causes a marked loss in ductility and aalloy and causes a marked loss in ductility and a greater susceptibility to corrosion.greater susceptibility to corrosion. • Thus it is not a good practice to place a newThus it is not a good practice to place a new amalgam restoration adjacent to a high nobleamalgam restoration adjacent to a high noble alloy restoration. In addition, these dissimilaralloy restoration. In addition, these dissimilar metals form a galvanic cell that can lead tometals form a galvanic cell that can lead to breakdown of the anode (amalgam) relative tobreakdown of the anode (amalgam) relative to the cathode (noble alloy).the cathode (noble alloy). www.indiandentalacademy.comwww.indiandentalacademy.com
  42. 42. • PorositiesPorosities in noble metal alloy castings may bein noble metal alloy castings may be classified as follows:classified as follows: • I. Solidification defectsI. Solidification defects • A. Localized shrinkage porosityA. Localized shrinkage porosity • B. MicroporosityB. Microporosity • II. Trapped gasesII. Trapped gases • A. Pinhole porosityA. Pinhole porosity • H. Gas inclusionsH. Gas inclusions • C. Subsurface porosityC. Subsurface porosity • III. Residual airIII. Residual air www.indiandentalacademy.comwww.indiandentalacademy.com
  43. 43. • Localized shrinkageLocalized shrinkage • generally caused by prematuregenerally caused by premature termination of the flow of molten metaltermination of the flow of molten metal during solidification.during solidification. • The linear contraction of noble metalThe linear contraction of noble metal alloys in changing from a liquid to a solidalloys in changing from a liquid to a solid is at least 1.25%. Therefore continualis at least 1.25%. Therefore continual feeding of molten metal through the spruefeeding of molten metal through the sprue must occur to make up for the shrinkagemust occur to make up for the shrinkage of metal volume during solidificationof metal volume during solidification www.indiandentalacademy.comwww.indiandentalacademy.com
  44. 44. • . If the sprue freezes in its cross-section. If the sprue freezes in its cross-section before this feeding is completed to thebefore this feeding is completed to the casting proper, a localized shrinkage voidcasting proper, a localized shrinkage void will occur in the last portion of the castingwill occur in the last portion of the casting that solidifies.that solidifies. www.indiandentalacademy.comwww.indiandentalacademy.com
  45. 45. Localized shrinkage porosity due to delayedLocalized shrinkage porosity due to delayed solidificationsolidification www.indiandentalacademy.comwww.indiandentalacademy.com
  46. 46. • The porosity in the pontic areaThe porosity in the pontic area • caused by the ability of the pontic tocaused by the ability of the pontic to retain heat because of its bulkretain heat because of its bulk • It was located in the heat center of theIt was located in the heat center of the ring.ring. www.indiandentalacademy.comwww.indiandentalacademy.com
  47. 47. • This problem can be solved by attachingThis problem can be solved by attaching one or more small-gauge spruesone or more small-gauge sprues • These small chill set sprues ensure thatThese small chill set sprues ensure that solidification begins within the sprues, andsolidification begins within the sprues, and they act as cooling pins to carry heat awaythey act as cooling pins to carry heat away from the pontic.from the pontic. www.indiandentalacademy.comwww.indiandentalacademy.com
  48. 48. • Suck-back porosity often occurs at anSuck-back porosity often occurs at an occlusoaxial line angle or incisoaxial lineocclusoaxial line angle or incisoaxial line angle that is not well rounded.angle that is not well rounded. • The entering metal impinges onto theThe entering metal impinges onto the mold sur­face at this point and creates amold sur­face at this point and creates a higher localized mold temperature in thishigher localized mold temperature in this region, known as aregion, known as a hot spothot spot www.indiandentalacademy.comwww.indiandentalacademy.com
  49. 49. Suckback - porositySuckback - porosity www.indiandentalacademy.comwww.indiandentalacademy.com
  50. 50. • AA hot spot may retain a localized pool of moltenhot spot may retain a localized pool of molten metal after other areas of the casting havemetal after other areas of the casting have solidified.solidified. • This in turn creates a shrinkage void or suck-This in turn creates a shrinkage void or suck- back porosity.back porosity. • Elimination by flaring the point of sprueElimination by flaring the point of sprue attachment and reducing the mold-meltattachment and reducing the mold-melt temperature differential, that is ,lowering thetemperature differential, that is ,lowering the casting temperature by about 30° C.casting temperature by about 30° C. www.indiandentalacademy.comwww.indiandentalacademy.com
  51. 51. MICROPOROSITY AND PINHOLEMICROPOROSITY AND PINHOLE POROSITYPOROSITY www.indiandentalacademy.comwww.indiandentalacademy.com
  52. 52. • MicroporosityMicroporosity • occurs from solidification shrinkage but isoccurs from solidification shrinkage but is generally present in fine-grain alloy castingsgenerally present in fine-grain alloy castings when the solidification is too rapid for thewhen the solidification is too rapid for the microvoids to segregate to the liquid pool.microvoids to segregate to the liquid pool. • Such phenomena can occur from rapidSuch phenomena can occur from rapid solidification if the mold or casting tem­peraturesolidification if the mold or casting tem­perature is too low.is too low. • This type of defect is not detectable unless theThis type of defect is not detectable unless the casting is sectioned.casting is sectioned. www.indiandentalacademy.comwww.indiandentalacademy.com
  53. 53. • pinhole and the gas inclusionpinhole and the gas inclusion porositiesporosities • are related to the entrapment of gasare related to the entrapment of gas during solidification.during solidification. • both are characterized by a sphericalboth are characterized by a spherical contour, but they are decidedly different incontour, but they are decidedly different in size.size. • The gas inclusion porosities are usuallyThe gas inclusion porosities are usually much larger than the pinhole porositymuch larger than the pinhole porosity www.indiandentalacademy.comwww.indiandentalacademy.com
  54. 54. • Many metals dissolve or occlude gasesMany metals dissolve or occlude gases while they are molten.while they are molten. • For example, both copper and silverFor example, both copper and silver dissolve oxygen in large amounts in thedissolve oxygen in large amounts in the liquid state.liquid state. • platinum and palladium have a strongplatinum and palladium have a strong affinity for hydrogen as well as oxygen.affinity for hydrogen as well as oxygen. • On solidification, the absorbed gases areOn solidification, the absorbed gases are expelled and pinhole porosity resultsexpelled and pinhole porosity results www.indiandentalacademy.comwww.indiandentalacademy.com
  55. 55. • The larger voids may also result from theThe larger voids may also result from the same cause, but it is more logical tosame cause, but it is more logical to assume that such voids are caused byassume that such voids are caused by gas that is mechanically trapped by thegas that is mechanically trapped by the molten metal in the mold or by gas that ismolten metal in the mold or by gas that is incorporated during the casting procedure.incorporated during the casting procedure. www.indiandentalacademy.comwww.indiandentalacademy.com
  56. 56. • All castings probably contain a certainAll castings probably contain a certain amount of porosity. However, the porosityamount of porosity. However, the porosity should be kept to a minimum because itshould be kept to a minimum because it may adversely affect the physicalmay adversely affect the physical properties of the casting.properties of the casting. www.indiandentalacademy.comwww.indiandentalacademy.com
  57. 57. • . Castings that are severely contaminated. Castings that are severely contaminated with gases are usually black when theywith gases are usually black when they are removed from the investment and doare removed from the investment and do not clean easily on pickling.not clean easily on pickling. www.indiandentalacademy.comwww.indiandentalacademy.com
  58. 58. A BLACK-COATED NOBLEA BLACK-COATED NOBLE METAL ALLOY CASTING FROMMETAL ALLOY CASTING FROM SULFUR CONTAMINATION ORSULFUR CONTAMINATION OR OXIDATIONOXIDATION www.indiandentalacademy.comwww.indiandentalacademy.com
  59. 59. • The porosity that extends to the surface isThe porosity that extends to the surface is usually in the form of small pinpoint holes.usually in the form of small pinpoint holes. When the surface is polished, otherWhen the surface is polished, other pinholes appear.pinholes appear. www.indiandentalacademy.comwww.indiandentalacademy.com
  60. 60. • Larger spherical porosities can be caused byLarger spherical porosities can be caused by gas occluded from a poorly adjusted torch flame,gas occluded from a poorly adjusted torch flame, or by use of the mixing or oxidizing zones of theor by use of the mixing or oxidizing zones of the flame rather than the reducing zone.flame rather than the reducing zone. • These types of porosity can be minimized byThese types of porosity can be minimized by pre-melting the gold alloy on a graphite cruciblepre-melting the gold alloy on a graphite crucible or a graphite block,or a graphite block, • by correctly adjusting and positioning the torchby correctly adjusting and positioning the torch flame during melting.flame during melting. www.indiandentalacademy.comwww.indiandentalacademy.com
  61. 61. • Subsurface porositySubsurface porosity may be caused bymay be caused by the simultaneous nucleation of solid grainsthe simultaneous nucleation of solid grains and gas bubbles at the first moment thatand gas bubbles at the first moment that the alloy freezes at the mold walls.the alloy freezes at the mold walls. • can be diminished by controlling the ratecan be diminished by controlling the rate at which the molten metal enters the mold.at which the molten metal enters the mold. www.indiandentalacademy.comwww.indiandentalacademy.com
  62. 62. • Entrapped-air porosity or Back pressureEntrapped-air porosity or Back pressure porosityporosity • occursoccurs on the inner surface of the casting,on the inner surface of the casting, • produce large concave depressions .produce large concave depressions . www.indiandentalacademy.comwww.indiandentalacademy.com
  63. 63. • This is caused by the inability of the air in theThis is caused by the inability of the air in the mold to escape through the pores in themold to escape through the pores in the investment or by the pressure gradient thatinvestment or by the pressure gradient that displaces the air pocket toward the end of thedisplaces the air pocket toward the end of the investment via the molten sprue and button.investment via the molten sprue and button. • The entrapment is frequently found in a "pocket"The entrapment is frequently found in a "pocket" at the cavity surface of a crown or mesio-at the cavity surface of a crown or mesio- occlusal-distal casting.occlusal-distal casting. www.indiandentalacademy.comwww.indiandentalacademy.com
  64. 64. • Occasionally, it is found even on the outsideOccasionally, it is found even on the outside surface of the casting when the castingsurface of the casting when the casting temperature or mold temperature is so low thattemperature or mold temperature is so low that solidification occurs before the entrapped air cansolidification occurs before the entrapped air can escape.escape. • The incidence of entrapped air can be increasedThe incidence of entrapped air can be increased by use of the dense modern investments, by anby use of the dense modern investments, by an increase in mold density produced by vacuumincrease in mold density produced by vacuum investing, and by the tendency for the mold toinvesting, and by the tendency for the mold to clog with residual carbon when the low-heatclog with residual carbon when the low-heat technique is used.technique is used. • Each of these factors tends to slow the ventingEach of these factors tends to slow the venting of gases from the mold during casting.of gases from the mold during casting. www.indiandentalacademy.comwww.indiandentalacademy.com
  65. 65. • Proper burnout, an adequate mold andProper burnout, an adequate mold and casting temperature, a sufficiently highcasting temperature, a sufficiently high casting pressure, and proper L/P ratio cancasting pressure, and proper L/P ratio can help to eliminate entrapped-air porosity. Ithelp to eliminate entrapped-air porosity. It is good practice to make sure that theis good practice to make sure that the thickness of investment between the tip ofthickness of investment between the tip of the pattern and the end of the ring not bethe pattern and the end of the ring not be greater than 6 mm.greater than 6 mm. www.indiandentalacademy.comwww.indiandentalacademy.com
  66. 66. CASTING DEFECTS BY RUDDCASTING DEFECTS BY RUDD AND MORROWAND MORROW • IncompleteIncomplete castingcasting  -Inadequate spruing-Inadequate spruing  -Alloy not hot enough-Alloy not hot enough  -Mold too cold-Mold too cold  -Ingate obstructed-Ingate obstructed  -Insufficient casting-Insufficient casting forceforce www.indiandentalacademy.comwww.indiandentalacademy.com
  67. 67. Rounded marginsRounded margins • Incomplete burnout ofIncomplete burnout of wax patternwax pattern www.indiandentalacademy.comwww.indiandentalacademy.com
  68. 68. • Insufficient heating ofInsufficient heating of alloybefore castingalloybefore casting • Margins melted whileMargins melted while attaching pattern toattaching pattern to sprue or formersprue or former • Improper length/diamImproper length/diam of sprue restricts flowof sprue restricts flow of alloy into moldof alloy into mold metal freezes beforemetal freezes before margins are completemargins are complete www.indiandentalacademy.comwww.indiandentalacademy.com
  69. 69. PorosityPorosity • Improper sprueImproper sprue former,size,length orformer,size,length or placementplacement www.indiandentalacademy.comwww.indiandentalacademy.com
  70. 70. Rough surface on castingRough surface on casting • Excess moisture onExcess moisture on patternpattern • Water powder ratioWater powder ratio too high in mixingtoo high in mixing investmentinvestment • Too much castingToo much casting pressure causingpressure causing investmentinvestment breakdown from forcebreakdown from force of alloyof alloy www.indiandentalacademy.comwww.indiandentalacademy.com
  71. 71. • ProlongedProlonged overheating ofoverheating of gypsum bondedgypsum bonded investmentinvestment www.indiandentalacademy.comwww.indiandentalacademy.com
  72. 72. Pits in castingPits in casting • Debris in mouldDebris in mould • Dirty waxDirty wax • Loose debris inLoose debris in cruciblecrucible • Mold temperature tooMold temperature too hothot www.indiandentalacademy.comwww.indiandentalacademy.com
  73. 73. Fins on castingFins on casting • Overvibration duringOvervibration during investment orinvestment or disturbing ring duringdisturbing ring during setset • Heating ring tooHeating ring too rapidly causesrapidly causes moisture in mold tomoisture in mold to form steam andform steam and rupture out moldrupture out mold www.indiandentalacademy.comwww.indiandentalacademy.com
  74. 74. Bubbles or nodules on castingBubbles or nodules on casting • Investment not mixedInvestment not mixed under enoughunder enough vacuum to removevacuum to remove entrapped air bubblesentrapped air bubbles www.indiandentalacademy.comwww.indiandentalacademy.com
  75. 75. • Air leak betweenAir leak between crucibles,spruecrucibles,sprue former,and castingformer,and casting allowed bubble toallowed bubble to form and becomeform and become trapped under patterntrapped under pattern www.indiandentalacademy.comwww.indiandentalacademy.com
  76. 76. www.indiandentalacademy.comwww.indiandentalacademy.com
  77. 77. • Incomplete CastingIncomplete Casting • Occasionally, only a partially completeOccasionally, only a partially complete casting, or perhaps no casting at all, iscasting, or perhaps no casting at all, is found. The obvious cause is that thefound. The obvious cause is that the molten alloy has been prevented, in somemolten alloy has been prevented, in some man­ner, from completely filling the mold.man­ner, from completely filling the mold. • At least two factors that may inhibit theAt least two factors that may inhibit the ingress of the liquefied alloy areingress of the liquefied alloy are • insufficient venting of the moldinsufficient venting of the mold • high viscosity of the fused metal.high viscosity of the fused metal. www.indiandentalacademy.comwww.indiandentalacademy.com
  78. 78. • The first consideration, insufficient venting,The first consideration, insufficient venting, is directly related to the back pres­sureis directly related to the back pres­sure exerted by the air in the mold.exerted by the air in the mold. • If the air cannot be vented quickly, theIf the air cannot be vented quickly, the molten alloy does not fill the mold before itmolten alloy does not fill the mold before it solidifies. In such a case, the magnitude ofsolidifies. In such a case, the magnitude of the casting pressure should be suspectedthe casting pressure should be suspected www.indiandentalacademy.comwww.indiandentalacademy.com
  79. 79. • . If insufficient casting pressure is used, the back. If insufficient casting pressure is used, the back pressure cannot be overcome. Furthermore, thepressure cannot be overcome. Furthermore, the pressure should be applied for at least 4 sec.pressure should be applied for at least 4 sec. • The mold is filled and the alloy is solidified in 1The mold is filled and the alloy is solidified in 1 sec or less; yet it is quite soft during the earlysec or less; yet it is quite soft during the early stages. Therefore the pressure should bestages. Therefore the pressure should be maintained for a few seconds beyond this point.maintained for a few seconds beyond this point. These failures are usually exemplified inThese failures are usually exemplified in rounded, incomplete margins.rounded, incomplete margins. www.indiandentalacademy.comwww.indiandentalacademy.com
  80. 80. Rounded,incomplete margins areRounded,incomplete margins are evidence of insufficient castingevidence of insufficient casting pressurepressure www.indiandentalacademy.comwww.indiandentalacademy.com
  81. 81. • A second common cause for anA second common cause for an incomplete casting is incompleteincomplete casting is incomplete elimination of wax residues fromelimination of wax residues from the mold. If too many products ofthe mold. If too many products of combustion remain in the mold, thecombustion remain in the mold, the pores in the investment maypores in the investment may become filled so that the air cannotbecome filled so that the air cannot be vented completelybe vented completely www.indiandentalacademy.comwww.indiandentalacademy.com
  82. 82. • If moisture or particles of wax remain, theIf moisture or particles of wax remain, the contact of the molten alloy with thesecontact of the molten alloy with these foreign substances produces an explosionforeign substances produces an explosion that may produce suffi­cient back pressurethat may produce suffi­cient back pressure to prevent the mold from being filled. Thisto prevent the mold from being filled. This shiny condition of the metal is caused byshiny condition of the metal is caused by the strong reducing atmosphere createdthe strong reducing atmosphere created by carbon monoxide left by the residualby carbon monoxide left by the residual wax.wax. www.indiandentalacademy.comwww.indiandentalacademy.com
  83. 83. Incomplete casting results fromIncomplete casting results from incomplete wax removalincomplete wax removal www.indiandentalacademy.comwww.indiandentalacademy.com
  84. 84. • Different alloys exibit varying viscosities inDifferent alloys exibit varying viscosities in molten state depending on composition andmolten state depending on composition and temperature.temperature. • However, both the surface ten­sion and theHowever, both the surface ten­sion and the viscosity of a molten alloy are decreased with anviscosity of a molten alloy are decreased with an increase in tempera­ture.increase in tempera­ture. • An incomplete casting resulting from too great aAn incomplete casting resulting from too great a viscosity can be attributed to insufficient heating.viscosity can be attributed to insufficient heating. The temperature of the alloy should be raisedThe temperature of the alloy should be raised higher than its liquidushigher than its liquidus www.indiandentalacademy.comwww.indiandentalacademy.com
  85. 85. • temperature so that its viscosity andtemperature so that its viscosity and surface tension are lowered and so that itsurface tension are lowered and so that it does not solidify prematurely as it entersdoes not solidify prematurely as it enters the mold. Such premature solidificationthe mold. Such premature solidification may account for the greater susceptibilitymay account for the greater susceptibility of the white gold alloys to porosityof the white gold alloys to porosity because their liquidus temperature arebecause their liquidus temperature are higher. Thus they are more difficult to melthigher. Thus they are more difficult to melt with a gas- air torch flame.with a gas- air torch flame. www.indiandentalacademy.comwww.indiandentalacademy.com
  86. 86. www.indiandentalacademy.comwww.indiandentalacademy.com
  87. 87. • Sprue former selection is based on the followingSprue former selection is based on the following five principles;five principles; • . For a small pattern a small size sprue is. For a small pattern a small size sprue is selected because a large sprue attached to aselected because a large sprue attached to a thin delicate pattern could cause distortionthin delicate pattern could cause distortion • A sprue former diameter if too thin will lead to aA sprue former diameter if too thin will lead to a shrinkage porosity (“suck- back) porosity.shrinkage porosity (“suck- back) porosity. • Reservoir sprues are used to overcome thisReservoir sprues are used to overcome this problem.problem. www.indiandentalacademy.comwww.indiandentalacademy.com
  88. 88. • 2-The sprue former should be attached to2-The sprue former should be attached to the portion of the pattern with the largestthe portion of the pattern with the largest cross sectional area. It is best for thecross sectional area. It is best for the molten alloy to flow from a thick section tomolten alloy to flow from a thick section to a surrounding thin area (e.g margins) anda surrounding thin area (e.g margins) and not the reverse. This design minimizes thenot the reverse. This design minimizes the risk for turbulence.risk for turbulence. www.indiandentalacademy.comwww.indiandentalacademy.com
  89. 89. • 3-The length of the sprue former should3-The length of the sprue former should be long enough to properly position thebe long enough to properly position the pattern in the casting ring within 6 mm ofpattern in the casting ring within 6 mm of the trailing end and yet short enough sothe trailing end and yet short enough so that molten alloy does not solidify before itthat molten alloy does not solidify before it fills the mold.fills the mold. www.indiandentalacademy.comwww.indiandentalacademy.com
  90. 90. • A reservoir should be added to a spruingA reservoir should be added to a spruing network to prevent localized shrinkage porosity.network to prevent localized shrinkage porosity. • When the molten metal alloy fills the heatedWhen the molten metal alloy fills the heated casting ring, the pattern area should solidify firstcasting ring, the pattern area should solidify first and the reservoir last. Because of its large massand the reservoir last. Because of its large mass of alloy and position in the heat centre of theof alloy and position in the heat centre of the ring, the reservoir remains molten to furnishring, the reservoir remains molten to furnish liquid alloy into the mold as it solidifies. Theliquid alloy into the mold as it solidifies. The resulting solidification shrinkage occurs in theresulting solidification shrinkage occurs in the reservoir bar and not in the restoration.reservoir bar and not in the restoration. www.indiandentalacademy.comwww.indiandentalacademy.com
  91. 91. • . Flaring facilitates the entry of fluid alloy. Flaring facilitates the entry of fluid alloy into the pattern area.into the pattern area. www.indiandentalacademy.comwww.indiandentalacademy.com
  92. 92. • Sprue Former Direction-Sprue Former Direction- The sprueThe sprue former should be directed away from anyformer should be directed away from any thin or delicate parts of the pattern,thin or delicate parts of the pattern, because the molten metal may abrade orbecause the molten metal may abrade or fracture investment in this area and resultfracture investment in this area and result in a casting failure. It should not bein a casting failure. It should not be attached at a right angle to a broad flatattached at a right angle to a broad flat surface as this leads to turbulence withinsurface as this leads to turbulence within the mold cavity and severe porosity in thethe mold cavity and severe porosity in the region. The sprue former should alwaysregion. The sprue former should always be attached to pattern at 45 degree angle.be attached to pattern at 45 degree angle. www.indiandentalacademy.comwww.indiandentalacademy.com
  93. 93. • Sprue Former Length-Sprue Former Length- The length of theThe length of the sprue former depends on the length of thesprue former depends on the length of the casting ring. The sprue length should becasting ring. The sprue length should be adjusted so that the top of the wax pattern isadjusted so that the top of the wax pattern is within 6 mm of the open end of the ring forwithin 6 mm of the open end of the ring for gypsum bonded investments. If the sprue is toogypsum bonded investments. If the sprue is too short, the wax pattern may be so far removedshort, the wax pattern may be so far removed from the end of the casting ring that gasesfrom the end of the casting ring that gases cannot be vented to permit the molten alloy to fillcannot be vented to permit the molten alloy to fill the ring completelythe ring completely www.indiandentalacademy.comwww.indiandentalacademy.com
  94. 94. • When these gases are not completelyWhen these gases are not completely eliminated porosity results. With the highereliminated porosity results. With the higher strength phosphate bonded investmentsstrength phosphate bonded investments the sprue former should be within 3 to 4the sprue former should be within 3 to 4 mm of the top of the investment. Themm of the top of the investment. The pattern should always be placed as closepattern should always be placed as close to the centre of the ring as possible.to the centre of the ring as possible. www.indiandentalacademy.comwww.indiandentalacademy.com
  95. 95. • The type, size, location, and direction ofThe type, size, location, and direction of the sprue are factors that contribute to thethe sprue are factors that contribute to the quality of the casting. A hollow sprue pinquality of the casting. A hollow sprue pin provides a stronger attachment to theprovides a stronger attachment to the pattern and is rec­ommended over thepattern and is rec­ommended over the solid pin. Where die solid sprue pin issolid pin. Where die solid sprue pin is necessary, as in some types of doublenecessary, as in some types of double sprues having a Y shape, a minutesprues having a Y shape, a minute amount of sticky wax should be used toamount of sticky wax should be used to enhance the union of the pin and the wax.enhance the union of the pin and the wax. www.indiandentalacademy.comwww.indiandentalacademy.com
  96. 96. • The diameter of the sprue, in conjunctionThe diameter of the sprue, in conjunction with the pressure of the casting machinewith the pressure of the casting machine and density of the molten metal, controlsand density of the molten metal, controls the rate of flow of the molten metal into thethe rate of flow of the molten metal into the mold cavity. The larger the diameter of themold cavity. The larger the diameter of the sprue or the higher the pressure of thesprue or the higher the pressure of the casting machine and density of the moltencasting machine and density of the molten metal, the faster the molten metal shouldmetal, the faster the molten metal should enter the mold cavityenter the mold cavity www.indiandentalacademy.comwww.indiandentalacademy.com
  97. 97. Localized shrinkage caused byLocalized shrinkage caused by using a sprue of improper diameterusing a sprue of improper diameter www.indiandentalacademy.comwww.indiandentalacademy.com
  98. 98. Detached sprue bcoz of turbulenceDetached sprue bcoz of turbulence caused by improper sprue anglecaused by improper sprue angle www.indiandentalacademy.comwww.indiandentalacademy.com
  99. 99. • Surface treatmentSurface treatment • Pickling consists of heating the discoloredPickling consists of heating the discolored casting in an acid. For gypsum bondedcasting in an acid. For gypsum bonded investments the best pickling solution is 50%investments the best pickling solution is 50% hydrochloric acid solution. It aids in the removalhydrochloric acid solution. It aids in the removal of any residual investment as well as of theof any residual investment as well as of the oxide coating.oxide coating. • Disadvantage is that acid fumes are likely toDisadvantage is that acid fumes are likely to corrode laboratory metal furnishings. Nevercorrode laboratory metal furnishings. Never should the casting be held with steel tongs soshould the casting be held with steel tongs so that both the casting and the tongs come inthat both the casting and the tongs come in contact with the pickling solution, as this maycontact with the pickling solution, as this may contaminate the casting.contaminate the casting. www.indiandentalacademy.comwww.indiandentalacademy.com
  100. 100. • Gold based and palladium based metalGold based and palladium based metal ceramic alloys and base metal alloys areceramic alloys and base metal alloys are bench cooled to room temperature beforebench cooled to room temperature before the casting is removed from thethe casting is removed from the investment. Castings from these alloys areinvestment. Castings from these alloys are generally not pickled, and when it isgenerally not pickled, and when it is recommended for certain metal –ceramicrecommended for certain metal –ceramic alloys, it is only to selectively removealloys, it is only to selectively remove specific surface oxides.specific surface oxides. www.indiandentalacademy.comwww.indiandentalacademy.com
  101. 101. CONCLUSIONCONCLUSION • An unsucessfull casting results in considerableAn unsucessfull casting results in considerable trouble and loss of time,in almost alltrouble and loss of time,in almost all instances,defects in casting can be avoided byinstances,defects in casting can be avoided by strict observance of procedures governed bystrict observance of procedures governed by certain fundamental rules and principles. Seldomcertain fundamental rules and principles. Seldom is a defect in a casting attributable to factorsis a defect in a casting attributable to factors others than the carelessness or ignorance of theothers than the carelessness or ignorance of the operator. With present techniques,castingoperator. With present techniques,casting failures should be the exception,not the rule..failures should be the exception,not the rule.. www.indiandentalacademy.comwww.indiandentalacademy.com
  102. 102. REFERENCESREFERENCES SCIENCE OF DENTAL MATERIALS---SCIENCE OF DENTAL MATERIALS--- ANUSAVICE—11ANUSAVICE—11THTH EDITIONEDITION CONTEMPORARY FIXEDCONTEMPORARY FIXED PROSTHODONTICS ---STEPHEN F.PROSTHODONTICS ---STEPHEN F. ROSENSTIEL---2ROSENSTIEL---2NDND EDITIONEDITION DENTAL LABORATORYDENTAL LABORATORY PROCEDURES---PROCEDURES--- RHOADS.RUDD.MORROWRHOADS.RUDD.MORROW  SCHILLINBURG . FUNDEMENTALSSCHILLINBURG . FUNDEMENTALS OF FIXED PROTHODONTICSOF FIXED PROTHODONTICS www.indiandentalacademy.comwww.indiandentalacademy.com
  103. 103. Thank you For more details please visit www.indiandentalacademy.com www.indiandentalacademy.comwww.indiandentalacademy.com

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