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Dental casting alloys/ oral surgery courses  

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Dental casting alloys/ oral surgery courses  

  1. 1. DENTAL CASTINGDENTAL CASTING ALLOYSALLOYS INDIAN DENTAL ACADEMYINDIAN DENTAL ACADEMY Leader in continuing Dental EducationLeader in continuing Dental Education www.indiandentalacademy.comwww.indiandentalacademy.com
  2. 2. INTRODUCTIONINTRODUCTION Because pure metals are apt to be soft and many tend to corrode rapidly andBecause pure metals are apt to be soft and many tend to corrode rapidly and also because of high cost their use is quite limited in dentistry. To optimizealso because of high cost their use is quite limited in dentistry. To optimize properties, most metals commonly used in dentistry are mixtures of two orproperties, most metals commonly used in dentistry are mixtures of two or more metallic elements or one or more metal and/or non metals (THEmore metallic elements or one or more metal and/or non metals (THE ALLOY).ALLOY). CASTING is one of the most widely used methods for fabrication of metalCASTING is one of the most widely used methods for fabrication of metal restorations out of the mouth. A pattern of lost tooth structure or the dentalrestorations out of the mouth. A pattern of lost tooth structure or the dental prosthesis to be reproduced in metal is constructed in wax. The wax isprosthesis to be reproduced in metal is constructed in wax. The wax is surrounded by an investment. After the investment has hardened the wax issurrounded by an investment. After the investment has hardened the wax is removed and the molten metal is forced into the mold space.removed and the molten metal is forced into the mold space. My seminar deals with these dental casting alloys.My seminar deals with these dental casting alloys. www.indiandentalacademy.comwww.indiandentalacademy.com
  3. 3. Contents  EvolutionEvolution  Desirable propertiesDesirable properties  ClassificationClassification  Microstructure of alloysMicrostructure of alloys  Alloys for all metal and resin veneered restorations.Alloys for all metal and resin veneered restorations.  High noble and noble alloys for metal ceramic prosthesis.High noble and noble alloys for metal ceramic prosthesis.  Base metal alloys for cast metal and metal ceramic prosthesisBase metal alloys for cast metal and metal ceramic prosthesis  Partial denture alloysPartial denture alloys  Review of literatureReview of literature  Alternatives to cast metal technologyAlternatives to cast metal technology  TroubleshootingTroubleshooting  Summary and conclusionSummary and conclusion  ReferencesReferences www.indiandentalacademy.comwww.indiandentalacademy.com
  4. 4. ““What we will be tomorrow is because of what we areWhat we will be tomorrow is because of what we are today, and what we are today is because of what wetoday, and what we are today is because of what we were yesterday.”were yesterday.” www.indiandentalacademy.comwww.indiandentalacademy.com
  5. 5. EVOLUTION OF DENTAL CASTING ALLOYSEVOLUTION OF DENTAL CASTING ALLOYS The history of dental casting alloys has been influenced by three majorThe history of dental casting alloys has been influenced by three major factorsfactors The technological changes of dental prostheses.The technological changes of dental prostheses. Metallurgic advancements.Metallurgic advancements. Price changes of noble metals since 1968Price changes of noble metals since 1968 www.indiandentalacademy.comwww.indiandentalacademy.com
  6. 6. Taggart’s presentation to the New York OdontologicalTaggart’s presentation to the New York Odontological Group in 1907 on the fabrication of cast inlay restorations oftenGroup in 1907 on the fabrication of cast inlay restorations often has been acknowledged as the first reported application of losthas been acknowledged as the first reported application of lost wax technique in dentistry.wax technique in dentistry. The inlay technique described by Taggart was an instantThe inlay technique described by Taggart was an instant success and it soon lead to the casting of complex restorationssuccess and it soon lead to the casting of complex restorations such as inlays, onlays, crowns, fixed partial dentures andsuch as inlays, onlays, crowns, fixed partial dentures and removable partial denture frameworks.removable partial denture frameworks. www.indiandentalacademy.comwww.indiandentalacademy.com
  7. 7. Because pure gold did not have physical properties requiredBecause pure gold did not have physical properties required for those dental restorations existing jewelry alloys were quicklyfor those dental restorations existing jewelry alloys were quickly adopted. These gold alloys were further strengthened with copper,adopted. These gold alloys were further strengthened with copper, silver or platinum.silver or platinum. In 1932 the dental materials Group at the National Bureau ofIn 1932 the dental materials Group at the National Bureau of Standards surveyed the alloys being used and roughly classifiedStandards surveyed the alloys being used and roughly classified them as a Type I, II, III and IV.them as a Type I, II, III and IV. In the following years several patents were issued for alloysIn the following years several patents were issued for alloys containing Palladium, as a substitute for Platinum.containing Palladium, as a substitute for Platinum. www.indiandentalacademy.comwww.indiandentalacademy.com
  8. 8. By 1948 the composition of dental noble metal alloys forBy 1948 the composition of dental noble metal alloys for lost metal restorations had become rather diverse, withlost metal restorations had become rather diverse, with these formulations, the tarnishing tendency of thethese formulations, the tarnishing tendency of the original alloys apparently had disappeared. It is noworiginal alloys apparently had disappeared. It is now known that in gold alloys Palladium is added toknown that in gold alloys Palladium is added to counteract the tarnishing potential of silver.counteract the tarnishing potential of silver. www.indiandentalacademy.comwww.indiandentalacademy.com
  9. 9. The base metal removable partial denture alloys wereThe base metal removable partial denture alloys were introduced in the 1930s. Since that time, both Ni-Cr and Co-introduced in the 1930s. Since that time, both Ni-Cr and Co- Cr formulati0ons have become increasingly popularCr formulati0ons have become increasingly popular compared with conventional type IV gold alloys, whichcompared with conventional type IV gold alloys, which previously were the predominant metals used for suchpreviously were the predominant metals used for such prostheses.prostheses. Likewise by 1978, the price of gold was climbing soLikewise by 1978, the price of gold was climbing so rapidly attention focused on the noble metal alloys. Torapidly attention focused on the noble metal alloys. To reduce the precious noble metal content and yet retain thereduce the precious noble metal content and yet retain the advantages of noble metals for dental use.advantages of noble metals for dental use. www.indiandentalacademy.comwww.indiandentalacademy.com
  10. 10. DESIRABLE PROPERTIES OF DENTALDESIRABLE PROPERTIES OF DENTAL CASTING ALLOYSCASTING ALLOYS BIOCOMPATIBILITYBIOCOMPATIBILITY CORROSION RESISTANCECORROSION RESISTANCE ALLERGENIC COMPONENTS IN CASTING ALLOYSALLERGENIC COMPONENTS IN CASTING ALLOYS ESTHETICSESTHETICS THERMAL PROPERTIESTHERMAL PROPERTIES MELTING RANGEMELTING RANGE COMPENSATION FOR SOLIDIFICATIONCOMPENSATION FOR SOLIDIFICATION STRENGTH REQUIREMENTSSTRENGTH REQUIREMENTS CASTABILITYCASTABILITY FINISHING OF CAST METALSFINISHING OF CAST METALS PORCELAIN BONDINGPORCELAIN BONDING ECONOMIC CONSIDERATIONSECONOMIC CONSIDERATIONS www.indiandentalacademy.comwww.indiandentalacademy.com
  11. 11. ““Even the proverbial needle in the haystackEven the proverbial needle in the haystack can be found if there is a system and methodcan be found if there is a system and method to the searchto the search”” www.indiandentalacademy.comwww.indiandentalacademy.com
  12. 12. CLASSIFICATION OF DENTAL CASTING ALLOYSCLASSIFICATION OF DENTAL CASTING ALLOYS ““Cast dental alloys can be classified according to the followingCast dental alloys can be classified according to the following five categories:five categories: 1. USE (All metal inlays, crowns and bridges, metal and1. USE (All metal inlays, crowns and bridges, metal and ceramic prostheses,ceramic prostheses, posts and cores, removable partialposts and cores, removable partial dentures, implants).dentures, implants). 2. MAJOR ELEMENTS :( Gold based, palladium based, silver2. MAJOR ELEMENTS :( Gold based, palladium based, silver based, nickel based, cobalt based and titanium based)based, nickel based, cobalt based and titanium based) 3. NOBILITY: High noble, noble, predominantly base metal.3. NOBILITY: High noble, noble, predominantly base metal. 4. PRINCIPAL THREE ELEMENTS: E.g.: Au-Pd-Ag, Pd-4. PRINCIPAL THREE ELEMENTS: E.g.: Au-Pd-Ag, Pd- Ag- Ni-Cr-BeAg- Ni-Cr-Be Co-Cr-Mo etcCo-Cr-Mo etc DOMINANT PHASE SYSTEM: Solid solution(substitutionalDOMINANT PHASE SYSTEM: Solid solution(substitutional type and inter metallic type),Coring, Eutectic, Peritectic, andtype and inter metallic type),Coring, Eutectic, Peritectic, and Intermetallic.Intermetallic. www.indiandentalacademy.comwww.indiandentalacademy.com
  13. 13. www.indiandentalacademy.comwww.indiandentalacademy.com
  14. 14. cc CCLASSIFICATION OF DENTAL CASTING GOLD ALLOYS: ISO DRAFT (2002) TYPE I: LOW STRENGTH: For castings subjected to very light stress ( inlays) the minimum yield strength is 80 MPa and the minimum % elongation is 18% TYPE II : MEDIUM STRENGTH : For castings subjected to high stress ( inlays, onlays and thin crowns ) the minimum yield strength is 180 MPa and % elongation is 10% TYPE III: HIGH STRENGTH : For castings subjected to high stress (onlays, thin copings, pontics, crowns, saddles) the minimum yield strength is 270 MPa and the minimum % elongation is 5% TYPE IV : EXTRA HIGH STRENGTH :For castings subjected to very high stress ( saddles, bars, clasps, single units and partial denture frameworks) the minimum yield strength is 360 MPa and the minimum % elongation is 3%www.indiandentalacademy.comwww.indiandentalacademy.com
  15. 15. MICROSTRUCTURE OF ALLOYSMICROSTRUCTURE OF ALLOYS METALMETAL: An element whose atomic structure rapidly loses electron to: An element whose atomic structure rapidly loses electron to form positively charged ions, and which exhibits metallic bonding,form positively charged ions, and which exhibits metallic bonding, opacity good light reflectance from a polished surface, and highopacity good light reflectance from a polished surface, and high electrical ands thermal conductivity.electrical ands thermal conductivity. Of the 103 elements listed in the periodic table 80 are classed as metalsOf the 103 elements listed in the periodic table 80 are classed as metals and they exhibit the following properties:and they exhibit the following properties: Metallic luster and metallic ringMetallic luster and metallic ring Opaque, harder, stronger and denser than other elementsOpaque, harder, stronger and denser than other elements Solids at room temperatureSolids at room temperature Good conductors of heat and electricity.Good conductors of heat and electricity. Ductile and malleableDuctile and malleable ElectropositiveElectropositive www.indiandentalacademy.comwww.indiandentalacademy.com
  16. 16. ALLOYALLOY: A crystalline substance with metallic properties that is: A crystalline substance with metallic properties that is composed of two or more chemical elements, at least one of which is acomposed of two or more chemical elements, at least one of which is a metal.metal. ALLOY SYSTEMALLOY SYSTEM is an aggregate of two or more metals in allis an aggregate of two or more metals in all combinations.combinations. In order to specify a particular alloy it is necessary to list theIn order to specify a particular alloy it is necessary to list the metals or elements present in the alloy and the amount of each elementmetals or elements present in the alloy and the amount of each element present. Two methods are available:present. Two methods are available: The weight percentage of each element.The weight percentage of each element. The atomic fraction or percentage.The atomic fraction or percentage. The properties of an alloy relate more to the atomic percentage.The properties of an alloy relate more to the atomic percentage. www.indiandentalacademy.comwww.indiandentalacademy.com
  17. 17. PHASE DIAGRAMS(CONSTITUTION DIAGRAMPHASE DIAGRAMS(CONSTITUTION DIAGRAM).). A graph of the phase field limits as a function of temperature andA graph of the phase field limits as a function of temperature and composition. Phase diagrams usually represent equilibrium conditions.composition. Phase diagrams usually represent equilibrium conditions. USES: They show the phases that are present in an alloy system forUSES: They show the phases that are present in an alloy system for different compositions and temperatures.different compositions and temperatures. www.indiandentalacademy.comwww.indiandentalacademy.com
  18. 18. www.indiandentalacademy.comwww.indiandentalacademy.com
  19. 19. PROPERTIES OF DIFFERENT ALLOYINGPROPERTIES OF DIFFERENT ALLOYING ELEMENTS:ELEMENTS: GOLDGOLD 1. Pure gold is soft, malleable, ductile metal that does not oxidize under1. Pure gold is soft, malleable, ductile metal that does not oxidize under atmospheric conditions and is attacked by only a few of the mostatmospheric conditions and is attacked by only a few of the most powerful oxidizing agents.powerful oxidizing agents. 2. It has a rich yellow color with a strong metallic luster.2. It has a rich yellow color with a strong metallic luster. 3. Although it is the most malleable and ductile metal, it ranks much3. Although it is the most malleable and ductile metal, it ranks much lower in strength.lower in strength. 4. The pure metal fuses at 1060 degree Celsius4. The pure metal fuses at 1060 degree Celsius 5. Small amounts of impurities have a pronounced effect on mechanical5. Small amounts of impurities have a pronounced effect on mechanical properties of gold and its alloysproperties of gold and its alloys www.indiandentalacademy.comwww.indiandentalacademy.com
  20. 20. 6. The specific gravity of pure gold is between19.30 and 19.33 making6. The specific gravity of pure gold is between19.30 and 19.33 making it one of the heavy metalsit one of the heavy metals 7. Air or water at any temperature doesn’t tarnish gold.7. Air or water at any temperature doesn’t tarnish gold. 8.BHN of 258.BHN of 25 9. Boiling point of 2970 degree Celsius9. Boiling point of 2970 degree Celsius 10.Linear coefficient of thermal expansion 0.14210.Linear coefficient of thermal expansion 0.142 PURITY OF GOLDPURITY OF GOLD The purity of gold is expressed in karat or finenessThe purity of gold is expressed in karat or fineness Karat refers to parts of pure gold in 24 parts of gold alloyKarat refers to parts of pure gold in 24 parts of gold alloy Fineness refers to parts of pure gold in 1000 parts of gold alloy.Fineness refers to parts of pure gold in 1000 parts of gold alloy. www.indiandentalacademy.comwww.indiandentalacademy.com
  21. 21. PALLADIUMPALLADIUM:: 1. Palladium is not used in pure state in dentistry but it is used in many1. Palladium is not used in pure state in dentistry but it is used in many dental alloys combined with either gold or silver.dental alloys combined with either gold or silver. 2. It is cheaper than platinum and since it imparts many of the properties2. It is cheaper than platinum and since it imparts many of the properties of platinum to dental alloys it is often used as a replacement forof platinum to dental alloys it is often used as a replacement for platinum.platinum. 3. Palladium is a white metal some what darker than platinum.3. Palladium is a white metal some what darker than platinum. 4. Its specific gravity is 11.4 i.e., about half that of platinum and a little4. Its specific gravity is 11.4 i.e., about half that of platinum and a little more than half of gold.more than half of gold. 5. It is a malleable and ductile metal with a melting point of1555 degree5. It is a malleable and ductile metal with a melting point of1555 degree Celsius which is the lowestCelsius which is the lowest of the platinum group of metals.of the platinum group of metals. 6. It hardens the alloy, imparts it whiter color and compensates the6. It hardens the alloy, imparts it whiter color and compensates the reddening effect of copper. Increase the melting point of the alloy andreddening effect of copper. Increase the melting point of the alloy and renders silver tarnish resistant.renders silver tarnish resistant. www.indiandentalacademy.comwww.indiandentalacademy.com
  22. 22. SILVERSILVER:: Silver is malleable, ductile, white in color and best known for itsSilver is malleable, ductile, white in color and best known for its conduction of heat and electricity. It is stronger and harder than gold butconduction of heat and electricity. It is stronger and harder than gold but softer than copper.softer than copper. Melting point of 960.5 degree CelsiusMelting point of 960.5 degree Celsius It combines with sulfur, chlorine and phosphorus or their vaporsIt combines with sulfur, chlorine and phosphorus or their vapors Pure silver is seldom employed in dental restorations because of thePure silver is seldom employed in dental restorations because of the black sulfide formation on the metal in the mouth although it is used asblack sulfide formation on the metal in the mouth although it is used as small additions to many gold alloys.small additions to many gold alloys. Addition of palladium to silver containing alloys prevents the rapidAddition of palladium to silver containing alloys prevents the rapid corrosion of such alloys in the oral environment.corrosion of such alloys in the oral environment. Silver increases the hardness slightly, whitens the alloy to over comeSilver increases the hardness slightly, whitens the alloy to over come the reddening effect of copper. Molten silver can dissolve oxygen andthe reddening effect of copper. Molten silver can dissolve oxygen and cause porosity in the casting and silver can encourage corrosion.cause porosity in the casting and silver can encourage corrosion.www.indiandentalacademy.comwww.indiandentalacademy.com
  23. 23. COPPERCOPPER 1.Hardens the alloy.1.Hardens the alloy. 2.Reduces the melting point of alloy.2.Reduces the melting point of alloy. 3. Reduces the density of the alloy3. Reduces the density of the alloy 4. Excessive copper renders the alloy more susceptible to tarnish4. Excessive copper renders the alloy more susceptible to tarnish and corrosion and reddens the alloy.and corrosion and reddens the alloy. ZINCZINC:: It is an oxide scavenger during melting of the alloy for castingIt is an oxide scavenger during melting of the alloy for casting procedure.procedure. in the absence of zinc silver absorbs oxygen at high temperaturein the absence of zinc silver absorbs oxygen at high temperature from the atmosphere. This oxygen is rejected during solidificationfrom the atmosphere. This oxygen is rejected during solidification tending to produce porosity in the castingtending to produce porosity in the casting www.indiandentalacademy.comwww.indiandentalacademy.com
  24. 24. IRIDIUM, RUTHENIUM AND RHODIUMIRIDIUM, RUTHENIUM AND RHODIUM:: Iridium is a hard metal that is quite brittle white with a high specificIridium is a hard metal that is quite brittle white with a high specific gravity of 22.42 and an exceptionally high melting point of 2440gravity of 22.42 and an exceptionally high melting point of 2440 degree Celsius.degree Celsius. 1.As little as 0.005% of Iridium is effective in refining the grain size1.As little as 0.005% of Iridium is effective in refining the grain size of cast gold alloys.of cast gold alloys. 2. Ruthenium produces a similar effect.2. Ruthenium produces a similar effect. GALLIUM:GALLIUM: Used mainly in silver free alloys to compensate for the decreasedUsed mainly in silver free alloys to compensate for the decreased thermal expansion seen in silver free alloys. (Silver is avoided inthermal expansion seen in silver free alloys. (Silver is avoided in metal ceramics as it has as greening effect)metal ceramics as it has as greening effect) IRON,TINIRON,TIN:: Increases the hardness. Also provides an oxide coat which improvesIncreases the hardness. Also provides an oxide coat which improves bonding of porcelain to alloy.bonding of porcelain to alloy.www.indiandentalacademy.comwww.indiandentalacademy.com
  25. 25. HEAT TREATMENT OF HIGH NOBLE ANDHEAT TREATMENT OF HIGH NOBLE AND NOBLE METAL ALLOYS:NOBLE METAL ALLOYS: HOMOGENIZATION:HOMOGENIZATION: The cast alloy is held at a temperature near its solidus to achieve theThe cast alloy is held at a temperature near its solidus to achieve the maximum amount of diffusion without melting (up to a period of 6maximum amount of diffusion without melting (up to a period of 6 hours in some instances)hours in some instances) This treatment allows atomic diffusion to occur which eliminates as-This treatment allows atomic diffusion to occur which eliminates as- cast compositionalcast compositional nonuniformity. This treatment results in:nonuniformity. This treatment results in: Increase in tarnish and corrosion resistance.Increase in tarnish and corrosion resistance. Increase in the ductility of the alloy.Increase in the ductility of the alloy. www.indiandentalacademy.comwww.indiandentalacademy.com
  26. 26. SOLUTION HEAT TREATMENTSOLUTION HEAT TREATMENT:: It involves heating the casting to a temperature below the solidusIt involves heating the casting to a temperature below the solidus (usually 700 degree Celsius) , holding for a short period of time(usually 700 degree Celsius) , holding for a short period of time (typically 10 min) so that the alloy returns to random substitutional(typically 10 min) so that the alloy returns to random substitutional solid solution , and then quenching to retain this atomic arrangementsolid solution , and then quenching to retain this atomic arrangement at room temperature.at room temperature. The tensile strength, hardness and proportional limit areThe tensile strength, hardness and proportional limit are reduced by such a treatment but the ductility is increased. Thisreduced by such a treatment but the ductility is increased. This treatment is indicated for structures that are to to be ground, shapedtreatment is indicated for structures that are to to be ground, shaped or otherwise cold worked, either in or out of the mouth.or otherwise cold worked, either in or out of the mouth. www.indiandentalacademy.comwww.indiandentalacademy.com
  27. 27. HARDENING HEAT TREATMENTHARDENING HEAT TREATMENT:: The age hardening of the dental alloys can be accomplished inThe age hardening of the dental alloys can be accomplished in several ways. One of the most practical hardening treatments is byseveral ways. One of the most practical hardening treatments is by SOAKING or AGEING the casting at a specific temperature for aSOAKING or AGEING the casting at a specific temperature for a definite time, usually 15 to 30 minutes, before it is water quenched.definite time, usually 15 to 30 minutes, before it is water quenched. The ageing temperature depends on the alloy composition but isThe ageing temperature depends on the alloy composition but is generally between 200 and 450 degree Celsius.generally between 200 and 450 degree Celsius. This treatment is indicated for metallic partial dentures,This treatment is indicated for metallic partial dentures, bridges and other similar structuresbridges and other similar structures.. www.indiandentalacademy.comwww.indiandentalacademy.com
  28. 28. CASTING SHRINKAGECASTING SHRINKAGE:: All metals and alloys of practical dental interest shrinkAll metals and alloys of practical dental interest shrink when they change from liquid to solid state. This occurs inwhen they change from liquid to solid state. This occurs in three stages:three stages: The thermal contraction of the liquid metal between theThe thermal contraction of the liquid metal between the temperature to which it is heated and the liquidus.temperature to which it is heated and the liquidus. The contraction of the metal inherent in its change fromThe contraction of the metal inherent in its change from the liquid to the solid state.the liquid to the solid state. The thermal contraction of the solid metal that occurs onThe thermal contraction of the solid metal that occurs on further cooling to room temperature.further cooling to room temperature. www.indiandentalacademy.comwww.indiandentalacademy.com
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  30. 30. SILVER PALLADIUM ALLOYSSILVER PALLADIUM ALLOYS:: These alloys are white and predominantly silver in composition butThese alloys are white and predominantly silver in composition but have substantial amounts of palladium at least 25%)have substantial amounts of palladium at least 25%) that provides nobility and promote tarnish resistance. They may orthat provides nobility and promote tarnish resistance. They may or may not have copper and a small amount of gold.may not have copper and a small amount of gold. ADVANTAGES:ADVANTAGES: Adequate strength properties.Adequate strength properties. Acceptable castabilityAcceptable castability Low costLow cost LIMITATION:LIMITATION: Great potential for tarnish and corrosion.Great potential for tarnish and corrosion. www.indiandentalacademy.comwww.indiandentalacademy.com
  31. 31. HIGH NOBLE AND NOBLE ALLOYS FOR METAL-HIGH NOBLE AND NOBLE ALLOYS FOR METAL- CERAMIC PROSTHESISCERAMIC PROSTHESIS In spite of vastly different chemical compositions all suchIn spite of vastly different chemical compositions all such alloys must share at least three common features:alloys must share at least three common features: They must have the potential to bond to dental porcelain.They must have the potential to bond to dental porcelain. They posses coefficients of thermal contraction compatible withThey posses coefficients of thermal contraction compatible with those ofthose of dental porcelains.dental porcelains. Their solidus temperature is sufficiently high to permit applicationTheir solidus temperature is sufficiently high to permit application of low fusing porcelains.of low fusing porcelains. The coefficients of thermal expansion tend to be reciprocal toThe coefficients of thermal expansion tend to be reciprocal to melting point of the alloys.melting point of the alloys. high sag resistance.high sag resistance. www.indiandentalacademy.comwww.indiandentalacademy.com
  32. 32. GOLD PALLADIUM SILVER ALLOYS (LOW SILVER CONTENT)GOLD PALLADIUM SILVER ALLOYS (LOW SILVER CONTENT) ADVANTAGESADVANTAGES:: EconomicalEconomical Excellent resistance to tarnish and corrosionExcellent resistance to tarnish and corrosion Relative freedom from technique sensitivityRelative freedom from technique sensitivity DISADVANTAGE:DISADVANTAGE: The potential for porcelain discoloration when silver vapor is released.The potential for porcelain discoloration when silver vapor is released. GOLD- PALLADIUM-SILVER ALLOYS (HIGH SILVER CONTENT)GOLD- PALLADIUM-SILVER ALLOYS (HIGH SILVER CONTENT) Gold alloys that contain 12% Ag or more account for approximatelyGold alloys that contain 12% Ag or more account for approximately 20% of the current alloy market.20% of the current alloy market. ADVANTAGES:ADVANTAGES: Lower costLower cost Favorable physical propertiesFavorable physical properties DISADVANTAGE:DISADVANTAGE: Potential for porcelain discoloration.Potential for porcelain discoloration.www.indiandentalacademy.comwww.indiandentalacademy.com
  33. 33. GOLD PALLADIUM ALLOYS:GOLD PALLADIUM ALLOYS: The first alloy of this type was introduced in 1977 by J.F.Jelenko andThe first alloy of this type was introduced in 1977 by J.F.Jelenko and Co. This alloy was designed to overcome the porcelain discolorationCo. This alloy was designed to overcome the porcelain discoloration effect (because it is silver free) and also to provide an alloy with a lowereffect (because it is silver free) and also to provide an alloy with a lower thermal contraction coefficient than that of either Au-Pd-Ag or Pd-Agthermal contraction coefficient than that of either Au-Pd-Ag or Pd-Ag alloys. Their gold content varies from 45 to 52% and palladium contentalloys. Their gold content varies from 45 to 52% and palladium content varies between 37-45%.varies between 37-45%. www.indiandentalacademy.comwww.indiandentalacademy.com
  34. 34. ADVANTAGESADVANTAGES:: These alloys are considered nearly ideal because:These alloys are considered nearly ideal because: Contain no silverContain no silver Their surface oxide layer is virtually indiscernibleTheir surface oxide layer is virtually indiscernible Their sag resistance is better than that of Au-Pt-Pd alloysTheir sag resistance is better than that of Au-Pt-Pd alloys Their castability, corrosion resistance and adherence to porcelain areTheir castability, corrosion resistance and adherence to porcelain are excellentexcellent Cost effectiveCost effective PROPERTIESPROPERTIES:: HV of about 200HV of about 200 Yield strength of 570 MPaYield strength of 570 MPa Elongation of 20%Elongation of 20% www.indiandentalacademy.comwww.indiandentalacademy.com
  35. 35. PALLADIUM GOLD ALLOYSPALLADIUM GOLD ALLOYS:: Relatively few alloys are available in the market due to the priceRelatively few alloys are available in the market due to the price volatility of palladium and their laboratory and clinical performance hasvolatility of palladium and their laboratory and clinical performance has not been adequately documented.not been adequately documented. PALLADIUM-GOLD-SILVER ALLOYSPALLADIUM-GOLD-SILVER ALLOYS:: These have a potential for porcelain discoloration. Gold content is fromThese have a potential for porcelain discoloration. Gold content is from 5-32% and silver content from 6.5-14%.5-32% and silver content from 6.5-14%. These alloys have a range of thermal contraction coefficients thatThese alloys have a range of thermal contraction coefficients that increase with an increase in silver contentincrease with an increase in silver content www.indiandentalacademy.comwww.indiandentalacademy.com
  36. 36. PALLADIUM-SILVER ALLOYSPALLADIUM-SILVER ALLOYS:: This alloy type was introduced in the market in 1974 as the first goldThis alloy type was introduced in the market in 1974 as the first gold free noble alloy available for metal ceramic restorationsfree noble alloy available for metal ceramic restorations The Pd content is 53-61% and 28-40% Ag in addition to tin and/orThe Pd content is 53-61% and 28-40% Ag in addition to tin and/or indium.indium. ADVANTAGES:ADVANTAGES: The low specific gravity and their low cost make them attractiveThe low specific gravity and their low cost make them attractive economic alternatives to gold based alloys.economic alternatives to gold based alloys. Adequate physical propertiesAdequate physical properties Alloys of this type are easy to polish and burnishAlloys of this type are easy to polish and burnish Adherence to porcelain is acceptable although a predominantlyAdherence to porcelain is acceptable although a predominantly mechanical type of bonding has been suggested for this alloy.mechanical type of bonding has been suggested for this alloy. DISADVANTAGESDISADVANTAGES:: Silver discoloration effect is most severe for these alloys. Gold metalSilver discoloration effect is most severe for these alloys. Gold metal conditioners or ceramic coating agents may minimize this effect. Inconditioners or ceramic coating agents may minimize this effect. In addition many of today’s porcelains are formulated to minimize thisaddition many of today’s porcelains are formulated to minimize this problemproblem www.indiandentalacademy.comwww.indiandentalacademy.com
  37. 37. PALLADIUM-COPPER-GALLIUM ALLOYSPALLADIUM-COPPER-GALLIUM ALLOYS:: First introduced in 1983, these alloys were very popular in 1990s.First introduced in 1983, these alloys were very popular in 1990s. However the price volatility of palladium required dentists to useHowever the price volatility of palladium required dentists to use otherother alloys. A brown or black oxide layer is formed during oxidation andalloys. A brown or black oxide layer is formed during oxidation and subsequent porcelain firing cycles. Because of all these factors thesesubsequent porcelain firing cycles. Because of all these factors these alloys have not been well accepted in the dental practice.alloys have not been well accepted in the dental practice. PALLADIUM-GALLIUM-SILVER ALLOYSPALLADIUM-GALLIUM-SILVER ALLOYS:: These alloys have a slightly lighter oxide layer than Pd-Cu alloys andThese alloys have a slightly lighter oxide layer than Pd-Cu alloys and they are thermally compatible with lower expansion porcelains. Inthey are thermally compatible with lower expansion porcelains. In addition they have a comparatively low hardness which allows the alloyaddition they have a comparatively low hardness which allows the alloy to be adjusted in the dental lab or the chair side.to be adjusted in the dental lab or the chair side. www.indiandentalacademy.comwww.indiandentalacademy.com
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  39. 39. •DISCOLORATION OF PORCELAIN BYDISCOLORATION OF PORCELAIN BY SILVERSILVER:: The colloidal dispersion of silver atoms entering the body and incisalThe colloidal dispersion of silver atoms entering the body and incisal porcelain or the glazed surface from vapor transport or surface diffusionporcelain or the glazed surface from vapor transport or surface diffusion may cause color changes including green, yellow-green, yellow-orange,may cause color changes including green, yellow-green, yellow-orange, orange and brown hues. This phenomenon is termed GREENING.orange and brown hues. This phenomenon is termed GREENING. Porcelains with higher sodium content are believed to exhibit morePorcelains with higher sodium content are believed to exhibit more intense discoloration because of more rapid silver diffusion in sodiumintense discoloration because of more rapid silver diffusion in sodium containing glass.containing glass. The intensity of discoloration increases for higher silver content alloys,The intensity of discoloration increases for higher silver content alloys, is more in the cervical region, lighter shades, multiple firing proceduresis more in the cervical region, lighter shades, multiple firing procedures and certain brands of porcelain and also in silver free alloys due toand certain brands of porcelain and also in silver free alloys due to vaporization of silver from the walls of contaminated furnaces.vaporization of silver from the walls of contaminated furnaces. www.indiandentalacademy.comwww.indiandentalacademy.com
  40. 40. PREVENTION OF DISCOLORATIONPREVENTION OF DISCOLORATION:: Use of ultra low fusing porcelain or non greening porcelainUse of ultra low fusing porcelain or non greening porcelain A pure gold film can be fired on a metal substrate to reduce the surfaceA pure gold film can be fired on a metal substrate to reduce the surface silver concentration.silver concentration. A ceramic conditioner can be fired as a barrier between the alloy andA ceramic conditioner can be fired as a barrier between the alloy and the porcelain.the porcelain. Use of a graphite block routinely to maintain a reducing atmosphere.Use of a graphite block routinely to maintain a reducing atmosphere. www.indiandentalacademy.comwww.indiandentalacademy.com
  41. 41. THERMAL COMPATIBILITY ANDTHERMAL COMPATIBILITY AND INCOMPATIBILITY OF METAL-CERAMICINCOMPATIBILITY OF METAL-CERAMIC SYSTEMSSYSTEMS Thermal compatibility refers to the ability of the metal and itsThermal compatibility refers to the ability of the metal and its veneering porcelain to contract at similar ratesveneering porcelain to contract at similar rates (thermal co efficient of expansion of metal is comparable in(thermal co efficient of expansion of metal is comparable in magnitude with the co efficient of thermal expansion of porcelainmagnitude with the co efficient of thermal expansion of porcelain.).) www.indiandentalacademy.comwww.indiandentalacademy.com
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  43. 43. PHYSICAL PROPERTIES OF HIGH NOBLE AND NOBLE ALLOYS BASE METAL ALLOYS FOR CAST METAL AND METAL CERAMIC PROSTHESIS The no of dental laboratories using base metal alloys steadily increased through 70s and 80s. Although the increased acceptance of these alloys during this period was greatly influenced by the price fluctuation of the noble metals, the trend continued through 90s even when the prices of noble metals had come down. The Ni-Cr-Be alloys have retained their popularity despite the potential toxicity of beryllium and the allergenic potential of nickel. www.indiandentalacademy.comwww.indiandentalacademy.com
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  45. 45. There are several reasons for the use of nickel chromium and/or cobalt chromium alloys in dentistry Nickel is combined with Chromium to form a highly corrosion resistant alloy Cost effectiveness Alloys such as Ticonium 100 have been used in re4movable partial denture frameworks for many years with few reports of allergic reactions. Although Beryllium is a toxic metal, dentists and patients should not be affected because the main risk occurs mainly in the vapor form which is a concern for the technician. Nickel alloys have excellent mechanical properties such as high elastic modulus, high hardness, high sag resistance and a reasonably high elongation (ductility) Lower density www.indiandentalacademy.comwww.indiandentalacademy.com
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  47. 47. On the other hand it is also important the realize the limitations of theseOn the other hand it is also important the realize the limitations of these alloys, particularly Vis-a –Vis metal ceramic restorations:alloys, particularly Vis-a –Vis metal ceramic restorations: These alloys are more difficult to cast and presolderThese alloys are more difficult to cast and presolder The ability to obtain acceptable fitting castings may require specialThe ability to obtain acceptable fitting castings may require special procedures to adequately compensate for the higher solidificationprocedures to adequately compensate for the higher solidification shrinkageshrinkage Potential for porcelain delamination as a result of separation of poorlyPotential for porcelain delamination as a result of separation of poorly adherent oxide layer from the metal substrate.adherent oxide layer from the metal substrate. Finishing and polishing require special procedures and is not easy eitherFinishing and polishing require special procedures and is not easy either in the lab or at chair side.in the lab or at chair side. Removal of defective restorationsRemoval of defective restorations may take time.may take time. Repair of crowns with fractured porcelain veneers which may be simplyRepair of crowns with fractured porcelain veneers which may be simply performed on noble metal substrates using pin-retained facings or metalperformed on noble metal substrates using pin-retained facings or metal ceramic onlays, is more difficult to accomplish in base metalceramic onlays, is more difficult to accomplish in base metal frameworksframeworks www.indiandentalacademy.comwww.indiandentalacademy.com
  48. 48. COMPOSITION AND PROPERTIES OF BASE METALCOMPOSITION AND PROPERTIES OF BASE METAL ALLOYS:ALLOYS: www.indiandentalacademy.comwww.indiandentalacademy.com
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  51. 51. PARTIAL DENTURE ALLOYS AND GUIDELINESPARTIAL DENTURE ALLOYS AND GUIDELINES FOR SELECTIONFOR SELECTION EFFECT OF EACH ALLOY CONSTITUENT:EFFECT OF EACH ALLOY CONSTITUENT: CHROMIUM:CHROMIUM: Chromium content is responsible for the tarnish resistance and stainlessChromium content is responsible for the tarnish resistance and stainless properties of these alloys. When the chromium of an alloy is over 30%properties of these alloys. When the chromium of an alloy is over 30% the alloy is more difficult to cast. It also forms a brittle phase known asthe alloy is more difficult to cast. It also forms a brittle phase known as the zigma phase. Therefore dental alloys of these types should notthe zigma phase. Therefore dental alloys of these types should not contain more than 28-29% chromium.contain more than 28-29% chromium. COBALT AND NICKEL:COBALT AND NICKEL: They are somewhat interchangeable to a certain extent. Cobalt increasesThey are somewhat interchangeable to a certain extent. Cobalt increases the elastic modulus, strength and harness of the alloy more than nickelthe elastic modulus, strength and harness of the alloy more than nickel does. Nickel may increase ductility.does. Nickel may increase ductility.www.indiandentalacademy.comwww.indiandentalacademy.com
  52. 52. CARBON CONTENT:CARBON CONTENT: The hardness of cobalt based alloys is increased by the increasedThe hardness of cobalt based alloys is increased by the increased content of carbon. A change in the carbon content in the order of 0.2 %content of carbon. A change in the carbon content in the order of 0.2 % in these alloys changes their properties to csuch an extent that the alloyin these alloys changes their properties to csuch an extent that the alloy would no longer be usable in dentistry.would no longer be usable in dentistry. ALUMINIUM:ALUMINIUM: Al in Ni containing alloys forms a compound of Nickel and AluminiumAl in Ni containing alloys forms a compound of Nickel and Aluminium (Ni3-Al).This compound increases the ultimate tenmsile and yield(Ni3-Al).This compound increases the ultimate tenmsile and yield strength.strength. BERYLLIUM:BERYLLIUM: 1 % of this element to Nickel based alloys reduces the fusion range of1 % of this element to Nickel based alloys reduces the fusion range of the alloy by about 100 degree Celsius. It also aids in solid solutionthe alloy by about 100 degree Celsius. It also aids in solid solution hardening. It improves the casting characteristics which possibly aid inhardening. It improves the casting characteristics which possibly aid in porcelain bondingporcelain bonding.. www.indiandentalacademy.comwww.indiandentalacademy.com
  53. 53. MOLYBDENUM:MOLYBDENUM: The presence of 3-6% molybdenum contributes to the strength of theThe presence of 3-6% molybdenum contributes to the strength of the alloy.alloy. SILICON AND MANGANESESILICON AND MANGANESE:: These are added to increase the castability of these alloys. They areThese are added to increase the castability of these alloys. They are present primarily on oxide to prevent oxidation of other elements duringpresent primarily on oxide to prevent oxidation of other elements during melting. . When the nitrogen content of the final alloy is more than 0.1melting. . When the nitrogen content of the final alloy is more than 0.1 % the castings loose some of their ductility since the minor ingredients% the castings loose some of their ductility since the minor ingredients of carbon, nitrogen and oxygen effectively increase the properties of theof carbon, nitrogen and oxygen effectively increase the properties of the final formulated and designed in such a way as to maximize the rigidityfinal formulated and designed in such a way as to maximize the rigidity of the prosthesis.of the prosthesis. www.indiandentalacademy.comwww.indiandentalacademy.com
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  57. 57. BIOLOGICAL HAZARDS AND PRECAUTIONSBIOLOGICAL HAZARDS AND PRECAUTIONS Lab technicians may be exposed occasionally or routinely toLab technicians may be exposed occasionally or routinely to excessively high concentrations of beryllium and nickel dustexcessively high concentrations of beryllium and nickel dust and beryllium vapor. Although the amount of berylliumand beryllium vapor. Although the amount of beryllium rarely exceeds 2% by weight, the atomic concentration ofrarely exceeds 2% by weight, the atomic concentration of beryllium is around 10.7%.beryllium is around 10.7%. The Occupational Health and Safety AdministrationThe Occupational Health and Safety Administration (OSHA) specifies that the exposure to beryllium dust in air(OSHA) specifies that the exposure to beryllium dust in air should be limited to a particulate beryllium concentration ofshould be limited to a particulate beryllium concentration of 2micrograms/m3 of air ( both respirable and nonrespirable2micrograms/m3 of air ( both respirable and nonrespirable particles) determined from an 8 hr time weighted average.particles) determined from an 8 hr time weighted average. www.indiandentalacademy.comwww.indiandentalacademy.com
  58. 58. The allowable maximum concentration is 5microgram/m3(not to beThe allowable maximum concentration is 5microgram/m3(not to be exceeded for a 15 min period). The National Institute for Occupationexceeded for a 15 min period). The National Institute for Occupation Safety and Health (NIOSH) recommends a limit of 0.5 micrograms /m3Safety and Health (NIOSH) recommends a limit of 0.5 micrograms /m3 based on a 130 min sample. Moffa et al reported that when a localbased on a 130 min sample. Moffa et al reported that when a local exhaust system was used the concentration of beryllium was reduced toexhaust system was used the concentration of beryllium was reduced to safe levels.safe levels. Physiologic responses to beryllium vary from contact dermatitis toPhysiologic responses to beryllium vary from contact dermatitis to severe chemical pneumonitis which can be fatal. Symptoms may rangesevere chemical pneumonitis which can be fatal. Symptoms may range from coughing, chest pain and general weakness to pulmonaryfrom coughing, chest pain and general weakness to pulmonary dysfunction.dysfunction. www.indiandentalacademy.comwww.indiandentalacademy.com
  59. 59. ALLERGY POTENTIAL OF NICKELALLERGY POTENTIAL OF NICKEL:: Of greater concern to dental patient is intra oral exposure toOf greater concern to dental patient is intra oral exposure to nickel, especially for patient with a known allergy to thisnickel, especially for patient with a known allergy to this element.element. Nickel allergy is determined by patch test using 5% NickelNickel allergy is determined by patch test using 5% Nickel sulfate. The effects of nickel exposure to humans havesulfate. The effects of nickel exposure to humans have included dermatitis, cancer of nasal sinus and larynx,included dermatitis, cancer of nasal sinus and larynx, irritation and perforation of nasal septum, loss of smell,irritation and perforation of nasal septum, loss of smell, asthmatic lung disease, pulmonary pneumoconiosis, lungasthmatic lung disease, pulmonary pneumoconiosis, lung dysfunction and death.dysfunction and death. OSHA standard: 8 hr time weighted average concentrationOSHA standard: 8 hr time weighted average concentration limit of 1000 microgram/m3 of nickel and nickel compoundslimit of 1000 microgram/m3 of nickel and nickel compoundswww.indiandentalacademy.comwww.indiandentalacademy.com
  60. 60. TITANIUM FOR CASTING APPLICATIONSTITANIUM FOR CASTING APPLICATIONS Titanium was first isolated then named 200 years ago but the metal weTitanium was first isolated then named 200 years ago but the metal we know is less than 40 years old. It is the fourth most abundant metal inknow is less than 40 years old. It is the fourth most abundant metal in the earth's crust. It is a reactive metal and hence difficult to extract. Dr.the earth's crust. It is a reactive metal and hence difficult to extract. Dr. Wilhelm Kroll invented useful metallurgical processes for theWilhelm Kroll invented useful metallurgical processes for the commercial production of titanium metal and hence he is called thecommercial production of titanium metal and hence he is called the father of titanium industry.father of titanium industry. PROPERTIES OF TITANIUMPROPERTIES OF TITANIUM The physical and mechanical properties of titanium and its alloys varyThe physical and mechanical properties of titanium and its alloys vary greatly with the addition of traces of other elements such as oxygen,greatly with the addition of traces of other elements such as oxygen, iron and nitrogen. Commercially pure Ti is available in four gradesiron and nitrogen. Commercially pure Ti is available in four grades (Grade I to Grade IV) based on the incorporation of small amounts of(Grade I to Grade IV) based on the incorporation of small amounts of oxygen, nitrogen, hydrogen, iron and carbon during purificationoxygen, nitrogen, hydrogen, iron and carbon during purification procedures.procedures. The most commonly used and important Ti alloy is Ti-6Al-4V alloyThe most commonly used and important Ti alloy is Ti-6Al-4V alloy because of its desirable proportion and predictable producibility.because of its desirable proportion and predictable producibility. www.indiandentalacademy.comwww.indiandentalacademy.com
  61. 61. PROPERTIES OF TITANIUM AND ITS ALLOY (Ti-PROPERTIES OF TITANIUM AND ITS ALLOY (Ti- 6Al-4V)6Al-4V) Ti is the most biocompatible metal used for dental prostheses.Ti is the most biocompatible metal used for dental prostheses. High melting point of 1668­­ degree Celsius.High melting point of 1668­­ degree Celsius. It is highly resistant to tarnish and corrosion due to the formation of aIt is highly resistant to tarnish and corrosion due to the formation of a coat of titanium oxide on the surface.coat of titanium oxide on the surface. But as the oxidation rate of Ti increases rapidly above a temperature ofBut as the oxidation rate of Ti increases rapidly above a temperature of 850 degree Celsius, it is desirable to use ultra low fusing porcelains for850 degree Celsius, it is desirable to use ultra low fusing porcelains for Ti­ceramic prostheses.Ti­ceramic prostheses. A density of 4.51, VHN of 130­210, % elongation of 15­24A density of 4.51, VHN of 130­210, % elongation of 15­24 yield strength of 241­548 MPayield strength of 241­548 MPa Melting point of 3035Melting point of 3035 www.indiandentalacademy.comwww.indiandentalacademy.com
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  63. 63. A special casting machine with arc melting capability and argonA special casting machine with arc melting capability and argon atmosphere is used along with a compatible investment are used toatmosphere is used along with a compatible investment are used to ensure acceptable castability.ensure acceptable castability. The most widely used Ti alloy used in dentistry is Ti­6Al­4VThe most widely used Ti alloy used in dentistry is Ti­6Al­4V which is a alpha­beta alloy. Although it is stronger than CP Ti, it is notwhich is a alpha­beta alloy. Although it is stronger than CP Ti, it is not as attractive from a biocompatibility point of view due to slow releaseas attractive from a biocompatibility point of view due to slow release of Al and V atoms in vivo.of Al and V atoms in vivo. www.indiandentalacademy.comwww.indiandentalacademy.com
  64. 64. REVIEW OF LITERATUREREVIEW OF LITERATURE P.J Brockhurst and R.W.S Canon in 1981 examined the requirements ofP.J Brockhurst and R.W.S Canon in 1981 examined the requirements of alloys for metal­ceramic crowns and bridgework and discussed thealloys for metal­ceramic crowns and bridgework and discussed the functional requirements and manipulative behavior of as well as cost offunctional requirements and manipulative behavior of as well as cost of alternatives to high gold alloys.alternatives to high gold alloys. They concluded that base metal alloys functioned satisfactorily asThey concluded that base metal alloys functioned satisfactorily as compared to highcompared to high noble alloys provided proper dental lab proceduresnoble alloys provided proper dental lab procedures were employed. Nickel and beryllium did not appear to be healthwere employed. Nickel and beryllium did not appear to be health hazards for themhazards for them www.indiandentalacademy.comwww.indiandentalacademy.com
  65. 65. J. Robert Kelly and Thomas C.Rose in 1983 discussed the variousJ. Robert Kelly and Thomas C.Rose in 1983 discussed the various physical properties, biocompatibility, porcelain bonding and corrosionphysical properties, biocompatibility, porcelain bonding and corrosion resistance of various non precious alloys and concluded that though theresistance of various non precious alloys and concluded that though the manipulation of non precious alloys is technique sensitive and exacting,manipulation of non precious alloys is technique sensitive and exacting, their better physical properties and clinical performance meritedtheir better physical properties and clinical performance merited consideration. They were of the opinion that beryllium was not a healthconsideration. They were of the opinion that beryllium was not a health hazard provided proper exhaust and ventilation was used in the dentalhazard provided proper exhaust and ventilation was used in the dental lab and that the allergenic potential of nickel needed further research.lab and that the allergenic potential of nickel needed further research. Russel R. Wang and Aaron Fenton in 1996 reviewed the literature onRussel R. Wang and Aaron Fenton in 1996 reviewed the literature on Titanium for prosthodontic applications. They described theTitanium for prosthodontic applications. They described the development and properties of titanium for the purpose of evaluating thedevelopment and properties of titanium for the purpose of evaluating the present status and future trends in its use.present status and future trends in its use. www.indiandentalacademy.comwww.indiandentalacademy.com
  66. 66. Selcuk Oruc and Ybrahim Tulunoglu in 2000 evaluated theSelcuk Oruc and Ybrahim Tulunoglu in 2000 evaluated the marginal and inner fit of metal –cramic restorations andmarginal and inner fit of metal –cramic restorations and frameworks made with a Nickel­Chromium alloy (Remaniumframeworks made with a Nickel­Chromium alloy (Remanium CS) and a commercially pure TitaniumCS) and a commercially pure Titanium (Rematitan). They(Rematitan). They concluded that the fit of base metal alloy metal ceramicconcluded that the fit of base metal alloy metal ceramic crowns was better than the commercially pure Titanium metalcrowns was better than the commercially pure Titanium metal ceramic crowns. However both the artificial crowns wereceramic crowns. However both the artificial crowns were clinically acceptable.clinically acceptable. www.indiandentalacademy.comwww.indiandentalacademy.com
  67. 67. A study was conducted in the dept. of prosthodontics ,under the able guidance of DR.N.P.Patil, to evaluate the effects of recasting on the mechanical properties like yield strength and percentage elongation of High Palladium alloys. It was concluded that: Both the high palladium alloys tested for mechanical properties like yield strength and percentage of elongation showed lesser values for the cast test samples as compared to the values given by the manufacturer. The test cast specimen made with new alloy and mixed alloy to50:50 proportion had almost same yield strength and percentage of elongation values for both alloys tested. www.indiandentalacademy.comwww.indiandentalacademy.com
  68. 68. Another study was conducted under the able guidance of Dr.N.P.Patil, in 1997, to evaluate the effect of heat cycles on the release of nickel and chromium from nickel­chromium base metal alloys. It was concluded that : There is a definite release of metal ions from the alloys used for restoration in the oral cavity. The release rate of metal ions was found to be maximum after 1 day and diminished over time. There was a significant difference in release of nickel ion from alloy A to alloy B and it was related to difference in chromium content. The amount of metal ions (nickel and chromium) released from these alloys may not cause systemic toxicity ,but the local effects on www.indiandentalacademy.comwww.indiandentalacademy.com
  69. 69. ALTERNATIVES TO CAST METALALTERNATIVES TO CAST METAL TECHNOLOGYTECHNOLOGY To avoid the challenges and cost associated with metal casting process,To avoid the challenges and cost associated with metal casting process, four technologies are availablefour technologies are available SINTERING OF BURNISHED FOIL:SINTERING OF BURNISHED FOIL: The Captek system consists of three pairs of materials:The Captek system consists of three pairs of materials: CaptekP layer which is adapted first to the die and fired at a temperatureCaptekP layer which is adapted first to the die and fired at a temperature of 1075 degree Celsiusof 1075 degree Celsius Captek G which is applied over the Captek P coping and the former isCaptek G which is applied over the Captek P coping and the former is drawn by capillary action into the network structure of the Captek Pdrawn by capillary action into the network structure of the Captek P coping vacated by the adhesive binder.coping vacated by the adhesive binder. Captek Repair paste and Capfil which are used to add material to CaptekCaptek Repair paste and Capfil which are used to add material to Captek structures.structures. The main ADVANTAGE of Captek structures is the very low thicknessThe main ADVANTAGE of Captek structures is the very low thickness of metal that can be achieved which ensures minimal tooth preparationof metal that can be achieved which ensures minimal tooth preparationwww.indiandentalacademy.comwww.indiandentalacademy.com
  70. 70. CAD-CAM PROCESSINGCAD-CAM PROCESSING A CAD­CAM System electronically or digitally records surface co­A CAD­CAM System electronically or digitally records surface co­ ordinates of the prepared tooth and stores these retrieved data in theordinates of the prepared tooth and stores these retrieved data in the memory of a computer. The image data can then be retrievedmemory of a computer. The image data can then be retrieved immediately to mill or grind a metal, ceramic or composite prosthesis byimmediately to mill or grind a metal, ceramic or composite prosthesis by computer control from a solid block of the chosen material. Withincomputer control from a solid block of the chosen material. Within minutes the prosthesis can be fabricated and placed in a prepared toothminutes the prosthesis can be fabricated and placed in a prepared tooth and bonded or cemented in the mouth of a patient.and bonded or cemented in the mouth of a patient. The optical scanning procedure eliminates the need forThe optical scanning procedure eliminates the need for anan impression. An advantage of ceramics is that homogeneous, high qualityimpression. An advantage of ceramics is that homogeneous, high quality materials with minimal porosity and other typical defects are designedmaterials with minimal porosity and other typical defects are designed for CAD­CAMfor CAD­CAM applications.applications. www.indiandentalacademy.comwww.indiandentalacademy.com
  71. 71. COPY MILLINGCOPY MILLING This process is based on the principle of tracing the surface of a patternThis process is based on the principle of tracing the surface of a pattern that is then replicated from a blank of ceramic, composite, or metal thatthat is then replicated from a blank of ceramic, composite, or metal that is ground, cut or milled by a rotating wheel whose motionis controlledis ground, cut or milled by a rotating wheel whose motionis controlled by a link through the tracing device. Eg : The Celay : Mikronaby a link through the tracing device. Eg : The Celay : Mikrona Technologies, Spreintenbach, Switzerland)Technologies, Spreintenbach, Switzerland) www.indiandentalacademy.comwww.indiandentalacademy.com
  72. 72. ELECTROFORMINELECTROFORMINGG A master cast of the prepared tooth is prepared and coated with a specialA master cast of the prepared tooth is prepared and coated with a special die spacer to facilitate separation of the duplicating material. Afterdie spacer to facilitate separation of the duplicating material. After applying a conductive silver layer to the duplicated surface (Gypsumapplying a conductive silver layer to the duplicated surface (Gypsum product) , the dieproduct) , the die is connected to a plating head and connected to ais connected to a plating head and connected to a power source and then placed in a plating solution. After a sufficientlypower source and then placed in a plating solution. After a sufficiently thick layer of gold or other material is deposited, the gypsum is removedthick layer of gold or other material is deposited, the gypsum is removed and the coping is sandblasted. Subsequent ceramic layers are condensedand the coping is sandblasted. Subsequent ceramic layers are condensed and sintered in a conventional way.and sintered in a conventional way. www.indiandentalacademy.comwww.indiandentalacademy.com
  73. 73. TROUBLESHOOTING: When combinations of dissimilar metals are in direct physical contact, GALVANIC CORROSION OR GALVANISM is produced. This may occur either due to two adjacent dissimilar crowns or two dissimilar opposing crowns. Hence care should be taken when two or more teeth are being restored. When the surface of crown is heterogeneous as regards to its composition and surface topography corrosion ensues. Especially solder joints. In case of surface irregularity such as roughness concentration cell corrosion is seen. These can be avoided by proper selection of alloy, proper heat treatment and immaculate finishing. The correct mass of alloy required for a casting a particular wax pattern is given by the formula: www.indiandentalacademy.comwww.indiandentalacademy.com
  74. 74. Mm = Dm x Mw Dw Where: Mm is mass of metal alloy Dm is density of the metal alloy Mw is mass of the wax pattern Dw is density of the wax pattern Because of difference in hardness, percentage elongation and ultimate tensile strength, different trimming and polishing techniques are employed for different alloys: Gold alloy: Carbide burs, Al oxide, rubber wheels, Tripoli or rouge Metal ceramic alloys: Carbide burs are preferred as Al oxide may contaminate with residual abrasive and interfere with bonding. Base alloys: Sand blasting or Carbide burs are used followed by electrolytic polishing. www.indiandentalacademy.comwww.indiandentalacademy.com
  75. 75. Summary and conclusionSummary and conclusion  ""INDIVIDUAL COMMITMENT TO A GROUPINDIVIDUAL COMMITMENT TO A GROUP EFFORT-THAT IS WHAT MAKES A TEAMEFFORT-THAT IS WHAT MAKES A TEAM WORK, A COMPANY WORK, A SOCIETYWORK, A COMPANY WORK, A SOCIETY WORK, A CIVILIZATION WORK."WORK, A CIVILIZATION WORK." www.indiandentalacademy.comwww.indiandentalacademy.com
  76. 76. References  Phillips’science of dental materials – Kenneth J.Anusavice,11Phillips’science of dental materials – Kenneth J.Anusavice,11thth Edition.Edition.  Removable partial prosthodontics­ McCracken,9Removable partial prosthodontics­ McCracken,9thth Edition.Edition.  Dental laboratory procedures – Fixed partial dentures ­RobertDental laboratory procedures – Fixed partial dentures ­Robert M. Murrow, Kenneth D. Rudd, John E. Rhoads.M. Murrow, Kenneth D. Rudd, John E. Rhoads.  Notes on Dental materials – E.C.Combe,6Notes on Dental materials – E.C.Combe,6thth Edition.Edition.  Contemporary Fixed Prosthodontics – Stephen F. Rosenstiel,Contemporary Fixed Prosthodontics – Stephen F. Rosenstiel, Martin F. Land, Junhei Fujimoto,3Martin F. Land, Junhei Fujimoto,3rdrd Edition.Edition.  Restorative dental materials – Robert G.Craig, John M.Restorative dental materials – Robert G.Craig, John M. Powers.Powers. www.indiandentalacademy.comwww.indiandentalacademy.com
  77. 77. Thank youThank you www.indiandentalacademy.comwww.indiandentalacademy.com

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