Dental Casting alloy

Dental Casting alloy for Dentistry

1. Dental Casting Alloys By Dr. Mujtaba Ashraf JR-1 Department of Prosthodontics 1 Mujtaba Ashraf

2. Contents: Introduction Historical Perspective Desirable Properties Composition Classification Noble Metal Alloys Base Metal Alloys Guidelines for the selection of alloys 2 Mujtaba Ashraf

3. Introduction: Today the dental profession has access to a wide variety of casting alloys. These alloys are designed for specific clinical purposes like: . Inlays . Onlays . Crowns . Bridges . Partial dentures; and . Porcelain fused to metal restorations. 3 Mujtaba Ashraf

4. ALLOY : A mixture of two or more metals or metalloids that are mutually soluble in the molten state; distinguished as binary, ternary, quaternary, etc., depending on the number of metals within the mixture. Alloying elements are added to alter the hardness, strength, and toughness of a metallic element, thus obtaining properties not found in a pure metal. *GPT8 4 Mujtaba Ashraf

5. Casting: Something that has been cast in a mold; an object formed by the solidification of a fluid that has been poured or injected into a mold. 5 Mujtaba Ashraf

6. Historical Perspective on Dental Casting Alloys Year Event 1789 Jean Darcet introduced Low-fusing metal alloy 1907 Introduction of Lost-Wax Technique by W.H.Taggart 1933 Replacement of Co-Cr for Gold in Removable Partial Denture 1950 Development of Resin Veneers for Gold Alloys 1959 Introduction of the Porcelain Fused-to-Metal Technique 1968 Palladium-Based Alloys as Alternatives to Gold Alloy 1971 Nickel-Based Alloys as Alternatives to Gold Alloys 1980s Introduction of All-Ceramic Technologies 1999 Gold Alloys as Alternatives to Palladium-Based Alloys 6 Mujtaba Ashraf

7. Desirable Properties of Dental Casting Alloys All casting alloys must first be biocompatible and then exhibit sufficient physical and mechanical properties to ensure adequate function and structural durability over long periods of time. Depending on the primary purpose of the prosthesis, such as to restore function, enhance aesthetics, or maintain occlusion, the choice of casting alloy or metal is made. 7 Mujtaba Ashraf

8. Some of the clinically important properties and requirements of the alloys are : Biocompatibility: The alloy should not react with the oral fluids and release any harmful products in oral environment. Resistance to tarnish: Tarnish is a thin film of a surface deposit or an interaction layer that is adherent to the metal surface. Tarnish is usually on silver alloys and on gold alloys with higher silver content. 8 Mujtaba Ashraf

9. Resistance to corrosion: Corrosion may lead to catastrophic failure; oxidized components may discolor natural teeth, porcelain veneers and soft tissues. Corrosion also contribute to galvanic shock due to the electrons released during corrosion. Released metallic components may cause metallic taste in the mouth. The presence of noble metals in alloy increases resistance to corrosion. 9 Mujtaba Ashraf

10. Nonallergenic: Although toxic materials are eliminated from the alloys. However, some individuals exhibits allergic reactions to some components. Since these allergic reactions are peculiar to the individual patient, the dentist should have a record of all the components of the alloy that is being used and should inform the patient accordingly. 10 Mujtaba Ashraf

11. Aesthetics: The alloys must be in optimal balance among the properties of aesthetics, fit, abrasive potential and clinical survivability. 11 Mujtaba Ashraf

12. Thermal Properties: For metal-ceramic restorations, the alloys or metals must have closely matching thermal expansion to be compatible with a given porcelain, and they must tolerate high processing temperatures. The melting range of alloys must be low enough to form smooth surfaces with the mold walls of the investment. 12 Mujtaba Ashraf

13. Liquidus and solidus temperatures: Liquidus temperature: Temperature at which an alloy begins to freeze on cooling or at which the metal is completely molten on heating. Solidus temperature: Temperature at which an alloy becomes solid on cooling or at which the metal begins to melt on heating. 13 Mujtaba Ashraf

14. Hence we can say that the melting of the alloys starts at solidus temperature and is completed at liquidus temperature. An alloy must be heated above its liquidus to be cast successfully. Alloys with the lower the solidus temperature is preferred as the lower shrinkage occurs during cooling. 14 Mujtaba Ashraf

15. Hardness : The hardness of an alloy should be sufficient enough to resist wear by the opposing tooth or restoration. At the same time, it should not be high enough to cause wear of the opposing enamel (VHN of enamel is 340 kg/mm ² ). Hardness of an alloy should not be less than 125 kg/mm ² or greater than 340 kg/mm ² . 15 Mujtaba Ashraf

16. Ease of fabrication: The material should be easily manipulated and the procedure for fabrication should not be too complicated and lengthy. 16 Mujtaba Ashraf

17. Castability: To achieve accurate details in a cast framework or prosthesis, the molten metal must able to wet the investment mold material very well and flow into the most intricate regions of the mold without any appreciable interaction with the investment and without forming porosity within the surface or sub surface region. 17 Mujtaba Ashraf

18. Finishing of cast metal: Some metals are harder, hence more difficult to finish and polish. Some noble metal alloys are more ductile and malleable, hence care should be taken during finishing of the casting. The hardness of an alloy is a good indicator of the difficulty in grinding and finishing of the alloy. 18 Mujtaba Ashraf

19. Porcelain Bonding: The alloy used in metal-ceramic restorations should be able to form a thin, adherent layer of oxide on its surface to enable proper bonding with ceramic. The alloy must have a coefficient of thermal expansion/contraction closely matching to that of ceramic so as to create compressive stresses to enhance fracture resistance of the ceramic. 19 Mujtaba Ashraf

20. Composition of Dental Casting Alloys Various metallic elements are combined in different proportions to produce alloys with adequate properties for dental applications. The metals that are used to make dental alloys are broadly of two major groups: Noble metals and Base metals 20 Mujtaba Ashraf

21. Noble Metal Alloys The periodic table of the elements shows eight noble metals: gold, the platinum group metals (platinum, palladium, rhodium, ruthenium, iridium, osmium), and silver. However, silver is more reactive in the oral cavity and is not considered a noble metal. 21 Mujtaba Ashraf

22. 22 Mujtaba Ashraf

23. GOLD Gold, a soft, yellow metal, is the most ductile and malleable of all metals but it has much lower strength. Density 19.3g/cm ³ Melting point 1063 ° C Resistance to corrosion High burnishability Low yield strength 23 Mujtaba Ashraf

24. Platinum, a bluish-white metal is tough, ductile and malleable. Its hardness is similar to that of copper Density 21.37g/cm ³ Melting point 1755°C (highest) Elevates fusion temperature Elevates strength Whitens the alloy PLATINUM 24 Mujtaba Ashraf

25. PALLADIUM Palladium, a white metal It whitens the alloy, any gold alloy containing more than 6% palladium will be white. Density 11.4g/cm3 Melting point 1555 ° C Enhance mechanical properties such as hardness and tensile strength Disadvantage: At elevated temperature, it has a great affinity for hydrogen gas. Consequently high Pd content castings may causes internal porosity by absorbing large amount gas, if not cast under ideal conditions. 25 Mujtaba Ashraf

26. Other Noble Metals Iridium (Ir) and ruthenium are used in small amounts in dental alloys as grain refiners to keep the grain size small. A small grain size is desirable because it improves the mechanical properties and uniformity of properties within an alloy Osmium (Os) has very high melting point and extreme cost, so are not used in dental casting alloys . 26 Mujtaba Ashraf

27. Rhodium (Rh) also has a high melting point (1966°C) and has been used in alloys with platinum to form wire for thermocouples. These thermocouples help measure the temperature in porcelain furnaces used to make dental restorations. 27 Mujtaba Ashraf

28. Base Metal Alloys Base metals used in dental alloys include silver, copper, zinc, indium, tin, gallium, and nickel. Uses Fabrication of partial denture frame work As casting and wrought alloys Surgical instruments Periodontal splints 28 Mujtaba Ashraf

29. SILVER (Ag) Silver is a malleable, ductile white metal. It is the best-known conductor of heat and electricity. Stronger and harder than gold but softer than copper. Density 10.4gms/cm 3 Melting point 961 o C It is unaltered in clean, dry air at any temperature, but combines with sulfur, chlorine, phosphorus, and vapors containing these elements or their compounds. Foods containing sulfur compounds cause severe tarnish on silver, and for this reason silver is not considered a noble metal in dentistry. 29 Mujtaba Ashraf

30. COPPER (Cu) Copper is a malleable and ductile metal with high thermal and electrical conductivity A characteristic red color. Copper forms a series of solid solutions with both gold and palladium and is therefore an important component of noble dental alloys. Melting point of 1083°C Density of 8.96 gm/cm³ 30 Mujtaba Ashraf

31. ZINC (Zn) Zinc is a blue-white metal with a tendency to tarnish in moist air. In its pure form, it is a soft, brittle metal with low strength. When heated in air, zinc oxidizes readily to form a white oxide of relatively low density. This oxidizing property is exploited in dental alloys. Although zinc may be present in quantities of only 1% to 2% by weight, it acts as a scavenger of oxygen when the alloy is melted. Thus zinc is referred to as a deoxidizing agent. 31 Mujtaba Ashraf

32. INDIUM (In) Indium is a soft, gray-white metal. Low melting point of 156.6° C. Indium is not tarnished by air or water. It is used in some gold-based alloys as a replacement for zinc and is a common minor component of some noble ceramic dental alloys. 32 Mujtaba Ashraf

33. TIN (Sn) Tin is a lustrous, soft, white metal Not to tarnish in normal air. Some gold-based alloys contain limited quantities of tin, usually less than 5% by weight. Tin is also an ingredient in gold-based dental solders. It combines with platinum and palladium to produce a hardening effect, but also increases brittleness. 33 Mujtaba Ashraf

34. GALLIUM (Ga) Gallium is a grayish metal. Stable in dry air but tarnishes in moist air. It has a very low melting point of 29.8° C Density of only 5.91 g/cm3. Gallium is not used in its pure form in dentistry, but is used as a component of some gold- and palladium based dental alloys, especially ceramic alloys. The oxides of gallium are important to the bonding of the ceramic to the metal. 34 Mujtaba Ashraf

35. NICKEL (Ni) Nickel has limited application in gold- and palladium-based dental alloys, but is a common component in nonnoble dental alloys. Melting point 1453° C Density of 8.91 g/cm3. When used in small quantities in gold-based alloys, nickel whitens the alloy and increases its strength and hardness. 35 Mujtaba Ashraf

36. Classification of Noble Metal Alloys All noble metal alloys have either gold or platinum as the principal metal by weight percentage. There are several classifications for dental casting alloys. The first (i.e. alloy type by nobility) being the simple classification given by ADA in 1984. Three categories are described high noble (HN), noble (N), and predominantly base metal (PB ) . 36 Mujtaba Ashraf

37. Alloy type by nobility A. Category I - High noble (HN) Alloys contain > 60 wt% of noble metals (Au > 40 wt%) B. Category II noble (N) Alloys contain > 25 wt% of noble metals. C. Category III predominantly base metal (PB) alloys contain < 25 wt% of noble metals. 37 Mujtaba Ashraf

38. Properties of High noble alloys These alloys are the most expensive as gold, palladium and platinum are expensive Have relatively high densities that make them easier to cast Due to high liquidus ( high melting point) allows them to serve as alloys for porcelain bonded restoration. Low corrosion properties 38 Mujtaba Ashraf

39. Properties of Noble alloys Moderate densities 10 to 12g/cm3 Corrosion resistance slight lower than HN alloy Cost of these alloys are less than NH alloy Used for crown or bridges with or without porcelain covering. 39 Mujtaba Ashraf

40. Properties of base metal alloys Extremely high yield strengths and hardness, makes difficult to polish. Less corrosion resistance. Less biocompatible . 40 Mujtaba Ashraf

41. Classification by Bureau of Standard, 1927 : Alloys can also be classified into four types according to their composition, their use, and the amount of stress they will be subjected to. This is the most prevalent classification. The hardness increases from type I to type IV. 41 Mujtaba Ashraf

42. Type I (soft-low strength): Used for fabrication of castings subjected to minimal stress. Minimum yield strength is 80 Mpa Minimum percent elongation 18% Used as inlays and class III and class V restorations. These alloys are easily burnishable. 42 Mujtaba Ashraf

43. B. Type II (medium- medium strength); Used for fabrication of castings subjected to moderate stresses Used for inlays, full crowns, onlays, and thick 3/4th crowns. The minimum yield strength is 180 Mpa. The minimum percent elongation is 10%. 43 Mujtaba Ashraf

44. C. Type III (hard high strength): For castings subjected to high stress . Used for fabrication of onlays, thin copings, thin 3/4th crowns, pontics, full crowns, and saddles. The minimum yield strength is 270 Mpa. The minimum percent elongation is 5%. 44 Mujtaba Ashraf

45. D. Type IV (extra hard- very high strength): Used for castings subjected to very high stresses such as saddles, bars, clasps, partial denture framework, and long span bridge framework. The minimum yield strength is 300 Mpa. The minimum percent elongation is 3%. Types 1 and 2 alloys are often referred to as inlay alloys. Types 3 and 4 alloys are generally called crown and bridge alloys. 45 Mujtaba Ashraf

46. The alloys for metal-ceramic restorations can be used for all-metal (or resin-veneer) prostheses, whereas the alloys for all-metal restorations should not be used for metal-ceramic restorations. The reasons are as follows: The alloys may not form thin, stable oxide layers to promote atomic bonding to porcelain. (2)Their melting range may be too low to resist sag deformation or melting at porcelain filing temperatures. ( 3 ) Their thermal contraction coefficients may not be close enough to those of commercial porcelains 46 Mujtaba Ashraf

47. Carat and Fineness For many years, noble alloys were described on the basis of their gold content, in terms of carat and fineness. Both refer only to the gold content of the alloy. Carat represents 1/24 th part of the whole. For example, 24-carat gold is pure (100% gold), whereas 22-carat gold (91.67% gold) is an alloy containing 22 parts pure gold and 2 parts of other metals. Fineness represents the number of parts of gold in 1000 parts of the alloy. Pure gold is 1000 fine. The use of these terms is less common nowadays. 47 Mujtaba Ashraf

48. ADA Specification No. 5 formerly classified gold alloys as types 1 to 4 depending on the content of gold, palladium, and platinum. The content of noble metals by weight ranges from 83% (type 1) to 75% (type 4). Both the current ADA Specification No. 5 (1997) and ISO Standard 1562 (2004) have classified four types of casting alloys using similar minimal yield strength and percent elongation values for each type of alloy. Gold Based Alloy 48 Mujtaba Ashraf

49. Gold Based alloys are generally yellow in color . Type 1 gold alloys Relatively Soft Au-83%; Ag-10%; Pd-0.5%; Cu-6%; Ga,In, & Zn-Balance Soft and designed for inlays supported by teeth and not subjected to significant mastication forces. 49 Mujtaba Ashraf

50. Type 2 gold alloys Medium strength Au-77%; Ag-14%; Pd-1%; Cu-7%; Ga,In, & Zn-Balance Widely used for inlays because of their superior mechanical properties, but they have less ductility than type 1 alloys. Used for conventional inlays onlays or full mouth crowns. 50 Mujtaba Ashraf

51. Type 3 gold alloys High Strength Au-75%; Ag-11%; Pd-3.5%; Cu-9%; Ga, In, & Zn-Balance Used for constructing crowns and onlays for high-stress areas. Increasing the Pt or Pd content raises the melting temperature, which is beneficial when components are to be joined. 51 Mujtaba Ashraf

52. Type 4 gold alloys Extra High Strength Au-56%; Ag-25%; Pd-4%; Cu-14%; Ga, In, & Zn-Balance Used in high-stress areas such as bridges and partial denture frameworks. The cast alloy must be rigid to resist flexure. Possess high yield strength to prevent permanent distortion, and be ductile enough for adjustment if the clasp of a framework has been distorted or needs adjustment. 52 Mujtaba Ashraf

53. Mujtaba Ashraf 53 High Noble and Noble Alloys for Metal Ceramic Prostheses Porcelain and ceramic materials have been used for fabricating esthetic dental restorations since the early 1800s. The first published reports describing the successful use of porcelain fused to alloys appeared in the mid-1950s.

54. Mujtaba Ashraf 54 Gold–platinum–palladium (Au–Pt–Pd) alloys This was the first casting alloy formulated for use with metal-ceramic restorations. This high noble alloy has a gold content of 8l%-87%; Pt 4.5%-10%, and Pd 5%-11%. The casting temperature is around l330 ° C-1335 ° C.

55. Mujtaba Ashraf 55 As with other high noble alloys, it has high corrosion resistance. This alloy is used exclusively for metal-ceramic prostheses (single crowns and short span bridges), it is contraindicated in long span bridges since its sag resistance is low and it is susceptible to dimensional change.

56. Mujtaba Ashraf 56 Gold–palladium–silver (Au–Pd–Ag) alloys The Au–Pd–Ag alloys were developed in an attempt to overcome the major disadvantages of the Au–Pt–Pd alloys: High cost, low hardness, and poor sag resistance. Subdivided in two smaller groups: High silver (More than 12% Ag) and Low silver (5%-11.99% Ag) The principle disadvantage of these alloys is the potential for their silver content to discolor porcelain

57. Mujtaba Ashraf 57 Greening It is the general term applied to porcelain that is discolored due to contamination with silver. Tuccillo suggested that silver may be responsible for staining when it evaporates as a positively charged ion during porcelain firing.

58. Mujtaba Ashraf 58 During firing the silver atoms enter the body of the porcelain or diffuse through the glazed surface and cause green, yellow-green, or yellow-orange to brown discoloration.

59. Mujtaba Ashraf 59 Prevention of greening: Regular use of a graphite block to maintain a reducing atmosphere near the alloy which inhibits the formation of silver oxide. A pure gold film is fired on the alloy surface; this reduces the amount of free silver ions available on the alloy surface for vaporization.

60. Mujtaba Ashraf 60 Gold–palladium (Au–Pd) alloys The Au–Pd alloys were developed to address the two main problems associated with silver-containing alloys: Porcelain discoloration and a high coefficient of thermal expansion. Introduced by J.F. Jelenko & Co in 1977 Contains 45%-52% Au and 37%-45% Pd

61. Mujtaba Ashraf 61 These alloys exhibit a “white gold” color and have been commercially successful. The only significant disadvantage is having a degree of thermal expansion incompatible with some high expansion porcelains causes crack formation. In an effort to address this problem, a number of Au–Pd alloys have recently been developed that contain less ( <5% silver) Due to these alloys low silver content, porcelain does not discolor, castability is improved, and the coefficient of thermal expansion is increased

62. Mujtaba Ashraf 62 Palladium–silver (Pd–Ag) alloys In 1974 the first “gold-free” noble-metal metal-ceramic alloys, the Pd–Ag alloys, were introduced. They were specifically developed to offer an economical alternative to more expensive gold-based alloys.

63. Mujtaba Ashraf 63 The compositions Pd-Ag alloys fall within a narrow range of 53% to 61% Pd and 28% to 40% Ag. Tin and/or indium are usually added to increase alloy hardness and to promote oxide formation and adequate bonding to porcelain.

64. Mujtaba Ashraf 64 The high silver content compared with that of gold-based alloys, the silver discoloration effect is most severe for these alloys. Gold metal conditioners or ceramic coating agents may minimize this effect. The elastic modulus for Pd–Ag alloys is the most favorable of all of the noble-metal metal-ceramic alloys as a result Pd–Ag alloys have excellent sag resistance.

65. Mujtaba Ashraf 65 High-palladium alloys Several types of high-palladium alloys were introduced in the 1980s. These alloys were primarily developed for economic reasons and to address biocompatibility concerns of nickel-based casting alloys, and to minimize the possibility of porcelain discoloration . The most popular types have been Pd–Cu, Pd–Co, and Pd–Ga .

66. Mujtaba Ashraf 66 Palladium-Gallium-Silver Palladium-gallium-silver alloys is the most recent of the noble metal alloys. Advantages Slightly lighter colored oxide than the Pd-Cu alloys. Thermally compatible. Low hardness

67. Mujtaba Ashraf 67 Base Metal Alloys Metals that oxidize or dissolve readily to release ions. Base metal alloys are primarily made of cobalt, nickel, and/or titanium; though minor amounts of noble metals may also be present.

68. Mujtaba Ashraf 68 These alloys are more complex, science they may contain 6-8 elements in addition to their primary constituents including: molybdenum, chromium, aluminum, vanadium, iron, carbon, beryllium, manganese, gallium, silicon, etc.

69. Mujtaba Ashraf 69 *(adapted from Naylor and O’Brien Compositional classification of base-metal metal-ceramic alloys

70. Mujtaba Ashraf 70 Historically, the base-metal alloys were divided into four groups: nickel–chromium–beryllium, nickel–chromium, nickel–high-chromium, and cobalt–chromium

71. Mujtaba Ashraf 71 Nickel–chromium–beryllium, nickel–chromium, nickel–high-chromium are used for fabrication of crowns and bridges (with and without ceramic). while cobalt–chromium predominantly used for removable partial dentures and dental implants.

72. Mujtaba Ashraf 72 Nickel–chromium (Ni–Cr) alloys Most common base metal alloy used in metal-ceramic prostheses. The composition includes: Nickel (61.5%-77.5% Chromium (12.8%-22%) Molybdenum (4%-14%) Aluminum (0%-4%), and Iron (0%-5%) Ni-Cr-Be alloys also contain 0%-2% beryllium

73. Mujtaba Ashraf 73 Yield strength is 260-830 MPa Hardness ranges between 175VHN -380 VHN Tensile strength 400-1200 MPa Modulus of elasticity 150-210 GPa Percentage elongation is 8%-28%

74. Mujtaba Ashraf 74 Chromium contributes to the corrosion resistance. Molybdenum decreases coefficient of thermal expansion. Nickel and aluminum form an intermetallic compound i.e Ni ₃Al that contributes to strength and hardness. Nickel is also a known allergen, more so in females (4.5%) than males (1.5%). It results in contact dermatitis and hypersensitivity OSHA regulations allow 15 μ g/m ³ of Ni in air.

75. Mujtaba Ashraf 75 Beryllium is primarily added to lowering the melting range of the alloy, enhances fluidity, and improves grain structure.

76. Mujtaba Ashraf 76 Beryllium is known to be toxic, more so to the laboratory technician during alloy melting. Toxicity that is termed as berylliosis may be exhibited from mild to moderate symptoms as contact dermatitis to severe chemical pneumonitis. Permissible maximum concentration of Be in air is 5 μ g/m ³ , while Occupational Safety and Health Act (OSHA) guidelines permit an exposure of a maximum of 2 μg/m ³.

77. Mujtaba Ashraf 77 Reasons for the use of nickel-chromium alloys in dentistry: Nickel is combined with chromium to form a highly corrosion resistant alloy. It is low cost alloy as compared to Gold based alloys. Alloys such as Ticonium-100 have been used in removable partial denture frameworks for many years with few reports of allergic reactions. Nickel alloys have excellent mechanical properties , such as high elastic modulus (stiffness), high hardness, and a reasonably high elongation (ductility).

78. Mujtaba Ashraf 78 Cobalt–chromium (Co–Cr) alloys In 1907 Haynes patented cobalt-chromium. In 1929 Co-Cr alloys were used in dental appliances. Cobalt is the main constituent of cobalt-based metal-ceramic alloys, with chromium added for strength and to provide corrosion resistance via passivation.

79. Mujtaba Ashraf 79 The composition of Co-Cr alloy is Cobalt (52%-28%) Chromium (15%-28%) Tungsten (10%-14%) Other trace elements are Ga 0%-7%, Ru (0%-6%), Fe (0%-1%) Cu (0%-1%)

80. Mujtaba Ashraf 80 Yield strength is 460-640 MPa Elastic modulus is 145-220 Gpa Elongation is 6%-15% Hardness is 330-465 VHN and Tensile strength is 520-820 MPa.

81. Mujtaba Ashraf 81 Cobalt–chromium alloys are the most common base-metal alternative for patients known to be allergic to nickel. Second highest melting point of all dental casting alloy. Disadvantages of Co-Cr alloys: Difficult laboratory procedures ( casting, finishing, polishing). Incompatibility in CTE between Co-Cr alloy and porcelain.

82. Mujtaba Ashraf 82 Co-Cr alloys are used for the metal framework of cast partial dentures, since they are much less ductile than Ni-Cr. These-alloys are not used for metal ceramic prostheses, since the oxide layer formed on these alloys are susceptible to delamination and adversely affect the bonding with porcelain

83. Mujtaba Ashraf 83 TITANIUM (Ti) AND TITANIUM ALLOYS Titanium was discovered in the late 1700s and is the fourth most abundant metal in the earth’s crust . Process for extracting of Titanium was introduced by Kroll in 1936.

84. Mujtaba Ashraf 84 Titanium has a number of advantages, such as light weight, adequate strength, good corrosion resistance, excellent biocompatibility. Titanium alloys are being used as dental implants For implant prosthesis, cast partial dentures and metal ceramic prostheses.

85. Mujtaba Ashraf 85 Titanium based alloys containing 90% titanium, 6% aluminum and 4% vanadium, hence this alloy is termed as Ti-6Al-4Va

86. Mujtaba Ashraf 86 Due to its high melting range ( upto 1668 °C), Ti-based alloys are difficult to cast and requires a special Centrifugal induction casting machine and argon atmosphere. Pure Cp-Ti has tensile strength of 240-890MPa Hardness 125-350VHN

87. Mujtaba Ashraf 87 Titanium has highest melting point of all metals and alloys used in dentistry High fusion temperature and low CTE. High corrosion resistance Titanium forms porous and non-adherent oxide layer which does not form reliable porcelain to metal bond.

88. Mujtaba Ashraf 88 GUIDELINES FOR THE SELECTION OF ALLOYS Choosing an alloy for prosthodontic restorations is a formidable task. Although there is no proven formula for selection, practitioners may find the following guidelines helpful.

89. Mujtaba Ashraf 89 Develop an understanding of alloys 1. Avoid selecting an alloy based on its color unless all other factors are equal. 2. Know the complete composition of alloys, and avoid elements to which the patient is allergic. Know the alloys that the laboratory uses; specify a specific alloy in the laboratory prescription.

90. Mujtaba Ashraf 90 3. When possible, use single-phase alloys over multiple-phase alloys. 4. Keep track of alloys used in the patient with the Identalloy system or something similar. At minimum, the name of the alloy and the manufacturer should be recorded.

91. Mujtaba Ashraf 91 Use clinically proven products from quality Manufacturers 5. Use alloys from companies that research and manufacture their own alloys. These companies will be able to provide the most accurate information, the best service, and the best answers when problems arise.

92. Mujtaba Ashraf 92 6. Use alloys that have been tested for elemental release and corrosion and that have the lowest possible release of elements. 7. Use a dental laboratory that is knowledgeable about its alloys and willing to discuss issues about them. Be comfortable with the alloys that the laboratory uses.

93. Mujtaba Ashraf 93 Develop a clinical philosophy 8. Focus on the long-term clinical performance and long-term costs of restorations rather than on short term costs.

94. Mujtaba Ashraf 94 9. Consider the clinical situation (esthetics, occlusion, space, and systemic allergy) when selecting an alloy. Select the alloy that meets the needs of the patient. Avoid a “one size fits all” approach. 10. Remember that the practitioner is ultimately responsible for the safety and efficacy of any restoration.

95. Mujtaba Ashraf 95 Conclusion It is not always possible or feasible to use noble or precious metals and alloys for fabrication of restorations. Moreover, most removable partial dentures are fabricated from chrome-cobalt alloys. Base metal alloys do have applications in dentistry, though noble metal alloys are superior in performance. Some patients may be allergic to some components of the base metal alloys and care should taken when fabricating such prostheses.

96. Mujtaba Ashraf 96 References Phillips Science Of Dental Material 10 th & 11 th Edition Restorative Dental Materials – Craig 13 th Edition Dental Materials And Their Selection- 3rd Edition By William J. O'brien Wataha Jc. Alloys For Prosthodontic Restorations. J Prosthet Dent 2002 Metal-ceramic Alloys In Dentistry: Howard W. Roberts; J Prosthet Dent Base Metal Alloys Used for Dental Restorations and Implants: Michael Roach

97. Mujtaba Ashraf 97