Alloys in fpd /dental education courses


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Alloys in fpd /dental education courses

  1. 1. 1 Alloys used in fixed prosthodontics ALLOYS USED IN FIXED PROSTHODONTICS INDIAN DENTAL ACADEMY Leader in continuing dental education
  2. 2. 2 Metal • A crystalline material that consists of positively charged ions in an ordered, closely packed arrangement and bonded with a cloud of electrons. This type of bond, called a metallic bond, is responsible for many of the properties of metals- electrical and thermal conductivity, metallic luster, and (usually) high strength
  3. 3. 3 Characteristic Properties Of Metals • Hard • Lustrous • Dense • Good conductors of heat and electricity • Opaque • Malleable and ductile • give electro positive ions in solution
  4. 4. 4 Occurrence • Metals occur either as pure elements or in compounds with other elements . Example; Gold (Au) Silver (Ag) pure element Copper Obtained as Cu2S, CuS Iron Obtained as Fe2O3 compounds
  5. 5. 5 Classification Of Metals • Pure Metal or Mixture of Metals – Alloys • Base Metal or Noble Metal • Cast metal or wrought metal
  6. 6. 6 Another Classification Of Metals • Light Metal – e.g., Al. • Heavy Metal – e.g., Fe. • High Melting Metal – e.g., Co, Cr. • Low Melting Metal – e.g., Sn. • High Ductile and Malleable metal – e.g., Au.
  7. 7. 7 Microscopic Structure Of Metals • Most metals have crystalline structure in solid state which are held together by metallic bonds. • Metals also exist in liquid state eg: Hg, in which crystalline alignment is lost and the atoms move freely in mass of liquid metal.
  8. 8. 8 Solidification Of Pure Metal • Pure metal has a melting point-known as Fusion Temperature, and has specific heat. • To melt a crystalline substance (metal) some what more heat energy is required to convert it from solid to liquid. • This extra heat is stored away within the atoms in the form of latent heat of fusion.
  9. 9. 9 Mechanism • When the solid metal changes into liquid, its crystalline pattern disappears, and the atoms are randomly distributed in the mass of liquid and they have more energy and are therefore move about freely. • In the reverse process of changing into solid, temperature of the melt goes gradually (cooling); atoms make an attempt to reform the crystalline arrangement.
  10. 10. 10 Mechanism of Crystallization • A pure metal may crystallize in a tree-branch pattern to form what is called a NUCLEUS • The initial nuclei are small in size and few in number known as EMBRYO, which do not stabilize in the melt and soon disappear. • As the temperature of the metal gradually goes down, a stable NUCLEUS is formed.
  11. 11. 11 • Such nucleus formations are called DENDRITES. • The metal is therefore made of thousands of tiny crystals, such a metal is called polycrystalline and each crystal in the structure is called a GRAIN.
  12. 12.
  13. 13. 13 GRAIN SIZE •The grain size can be altered by heating. • When the metal is heated and rapidly quenched, small grains are formed • when they are allowed to cool slowly, large grains are formed • The more fine the grain structure, the more uniform and better are the properties.
  14. 14. 14 Crystal Space Lattice • The formed crystals in a metal are arranged in a orderly pattern – layer by layer in regular stacks. • The crystals of a metal is in the form of a space lattice. • The type of space lattice varies from metal to metal.
  15. 15. 15 Crystal Space Lattice
  16. 16.
  17. 17. 17 Alloys • Combination of two or more metals which are generally mutually soluble in the liquid condition. • A metallic material formed by the intimate blending of 2 or more metals some times a non- metal be added. • A substance composed of 2 or more elements at least one of which is a metal.
  18. 18. 18 Methods of alloying • Melting – together the base metal (main) and the alloying element, mixing them thoroughly, and allowing the mixture to cool and solidify. This is a common method. • Sintering or by powder metallurgy – Metals are powdered, mixed and pressed to the desired shape and then heated but not melted till the powders unite to form a solid mass.
  19. 19. 19 Objectives of alloying 1. To increase hardness and strength. 2. To lower the melting point. 3. To increase fluidity of liquid metal. 4. To increase resistance to tarnish and corrosion. 5. To make casting or working on the metal easy. 6. To change the microscopic structure of the metal. 7. To change the color of the metal. 8. To provide special electrical and magnetic properties.
  20. 20. 20 CLASSIFICATION OF ALLOYS 1. Acc to Uses » All metal inlays » Crown and bridges » Metal ceramic restorations » Removable partial dentures 2. Major element present…. » Ferrous alloys-iron » Gold and silver alloys » Babbit metals-tin and lead » Nickel alloys
  21. 21. 21 3. Nobility (ADA 1984)…..  High noble  Noble  Base metal  Au-Pd-Ag  Pd-Ag-Sn  Co-Cr-Mo  Ti-Al-V 4. Principle three elements….
  22. 22. 22 5. Based on Yield strength & elongation…  Soft  Medium  Hard  Extra hard Isomorpous Eutectic Peritectic Intermetallic compound 6. Based on dominant phase….
  23. 23. 23 7. Based on method of fabrication….  Cast metal  Wrought metal 8.Based on the number of metals….  Binary  Ternary  Quaternary
  24. 24. 24 SOLID SOLUTIONS OR ISOMORPHOUS STATE OR SINGLE PHASE • Solid solution is nothing but solution in the solid state. • It consists of a solute and a solvent. • Solvent is that metal whose space lattice persists and solute is the other metal. E.g. Au – Ag Au – Cu Au – Pt Au – Pd Ag – Pd
  25. 25. 25 The solid solution can be either : 1.SUBSTITUTIONAL SOLID SOLUTION – Regular or Ordered – Random or Disordered
  27. 27. 27 Conditions Favoring Solid-Solubility • Atom size - if the atom sizes of the mixing metal are same, it will produce solid solution type of alloy. • Valency - metals of the same valency will produce solid- solution alloy. • Crystal structure- Only metals with the same type of crystal lattice can form a series of solid solutions. • Chemical affinity - must be less to produce solid- solution alloy.
  28. 28. 28 A B metal solution Freezing temp Freezing range T E M P E R A T U R E Time in minutes Cooling curve of a solid solution
  30. 30. 30 PROPERTIES OF A SOLID SOLUTION ALLOY The solid solution possesses: • Increased hardness • Increased strength • Increased proportional limit • Decreased ductility • Decreased resistance to corrosion due to coring • Melting range rather than a point
  31. 31. 31 EUTECTIC ALLOYS • The eutectic alloy is one in which the components exhibit complete solubility in the liquid state but limited solid solubility • The term eutectic means lowest melting point. • In silver copper system the temperature of silver is around 960.5°C and that of copper is 1083° C. But that of the eutectic composition is 779.4° C.
  32. 32. 32 • a mixture of salt and ice • These in contrast to other alloys do not have a solidification range ; instead they have a solidification point. • It can be written as : LIQUID = α SOLID SOLUTION + ß SOLID SOLUTION
  34. 34. 34 PROPERTIES OF EUTECTIC ALLOYS • Since there is a heterogeneous composition, they are susceptible to electrolytic corrosion. • They are brittle, because the present of insoluble phases inhibits slip. • They have a low melting point and therefore are important as solders.
  35. 35. 35 PERITECTIC ALLOYS • Peritectic is a phase where there is limited solid solubility. • They are not of much use in dentistry except for silver tin system. • This type of reaction occurs when there is a big differences in the melting points of the components.
  36. 36. 36 Phase diagram of peritectic alloy
  37. 37. 37 Inter metallic Compounds • Inter metallic compounds are those when the metals are soluble in the liquid state but unite and form a chemical compound on solidifying. • E.g. – Ag3 – Sn, – Sn7 – Hg8 • They are called inter metallic compounds because the alloy is formed by a chemical reaction between a metal and metal.
  38. 38. 38 Heat Treatment • Heat treatment (not melting) of metals in the solid state is called SOLID STATE REACTIONS. • This is a method to cause diffusion of atoms of the alloy by heating a solid metal to a certain temperature and for certain period of time. • This will result in the changes in the microscopic structure and physical properties.
  39. 39. 39 • Important criteria in this process are: 1.Composition of alloy 2.Temperature to which it is heated 3.Time of heating 4.Method of cooling - cooling slowly in the air or quenching rapidly in cold water.
  40. 40. 40 Purpose of Heat Treatment • Shaping and working on the appliance in the laboratory is made easy when the alloy is soft. This is the first stage and is called softening heat treatment. • To harden the alloy for oral use, so that it will withstand oral stresses. The alloy is again heated and this time it is called hardening heat treatment.
  41. 41. 41 Types of Heat Treatment  Softening Heat treatment  Hardening Heat treatment  Solution Heat treatment  Age Hardening
  42. 42. 42 Softening heat treatment • Also known as ANNEALING. This is done for structures which are cold worked. • Technique - alloy is placed in an electric furnace at a temperature of 700°C for 10 minutes and then rapidly cooled (quenched). • Result of this is reduction in strength, hardness and pro-portional limit but increase in ductility. In other words the metal becomes soft. This is also known as HOMOGENIZATION TREATMENT.
  43. 43.
  44. 44. 44 Hardening heat treatment • This is done for cast removable partial dentures, saddles, bridges, but not for Inlays. • Technique - The appliance (alloy) is heat soaked at a temperature between 200-450°C for 15-30 minutes and then rapidly cooled by quenching.
  45. 45. 45 • The result of this is increase in strength, hardness and proportional limit but reduction in ductility. • Also known as ORDER HARDENING or PRECIPITATION HARDENING.
  46. 46. 46 Solution Heat Treatment Or Solution-Hardening • When the alloy is heat soaked, any precipitations formed during earlier heat treatment, will now once again become soluble in the solvent metal.
  47. 47. 47 Age Hardening • After solution heat treatment, the alloy is once again heated to bring about further precipitation and this time it shows in the metallography as a fine dispersed phase. • This also causes hardening of the alloy and is known as age hardening because the alloy will maintain its quality for many years.
  48. 48. 48 Different Metals Used….. Gold (Au) • provides a high level of corrosion and tarnish resistance • increases an alloy's melting range slightly. • improves workability, burnish ability, and raises the density . • However, gold imparts a very pleasing yellow color to an alloy (if present in sufficient quantity).
  49. 49. 49 Palladium • increase the strength, hardness (with copper), corrosion and tarnish resistance of gold-based alloys. • will elevate an alloy's melting range and improve its sag resistance. • has a very strong whitening effect • possesses a high affinity for hydrogen, oxygen, and carbon. • lowers the density of the gold-based alloys slightly but has little similar effect on silver-based metals.
  50. 50. 50 Platinum • Platinum increases the strength, melting range, and hardness of gold-based alloys while improving their corrosion, tarnish, and sag resistance. • It whitens an alloy and increases the density of non gold-based metals because of its high density.
  51. 51. 51 Iridium • serves as a grain refiner for gold- and palladium-based alloys • improve the mechanical properties as well as the tarnish resistance.
  52. 52. 52 Ruthenium • Ruthenium acts as a grain refiner for gold- and palladium- based alloys • Improve their mechanical properties and tarnish resistance (like iridium).
  53. 53. 53 Silver • lowers the melting range, improves fluidity, and helps to control the coefficient of thermal expansion in gold- and palladium-based alloys • Silver-containing porcelain alloys have been known to induce discoloration (yellow, brown, or green) with some porcelains.
  54. 54. 54 • Silver possesses a high affinity for oxygen absorption, which can lead to casting porosity • However, small amounts of zinc or indium added to gold and silver-based alloys help to control silver's absorption of oxygen. • Silver will also corrode and tarnish in the presence of sulfur. Although silver is a precious element, it is not universally regarded as noble in the oral cavity .
  55. 55. 55 Aluminium • lowers the melting range of nickel-based alloys. • Act as a hardening agent and influences oxide formation. • With the cobalt - chromium alloys used for metal ceramic restorations, aluminum is one of the elements that is "etched" from the alloy's surface to create micromechanical reten-tion for resin- bonded retainers (Maryland Bridges).
  56. 56. 56 Beryllium • Like aluminum, beryllium lowers the melting range of nickel-based alloys, improves castability, improves polishability, is a hardener, and helps to control oxide formation. • The etching of nickel-chromium-beryllium alloys removes a Ni-Be phase to create the micro retention so important to the etched metal resin-bonded retainer. • Questions have been raised as to potential health risks to both technicians and patients associated with beryllium-containing alloys .
  57. 57. 57 Boron • Boron is a deoxidizer. • For nickel-based alloys, it is a hardening agent and an element that reduces the surface tension of the molten alloy to improve castability. • The nickel-chromium beryllium-free alloys that contain boron will pool on melting, as opposed to the Ni-Cr-Be alloys that do not pool. • Boron reduces ductility and increases hardness.
  58. 58. 58 Chromium • Chromium is a solid solution hardening agent that contributes to corrosion resistance by its passivating nature in nickel- and cobalt-based alloys.
  59. 59. 59 Cobalt • Cobalt is an alternative to the nickel- based alloys, but the cobalt-based metals are more difficult to process. • Cobalt is included in some high- palladium alloys to increase the alloy's coefficient of thermal expansion and to act as a strengthener
  60. 60. 60 Copper • Copper serves as a hardening and strengthening agent, can lower the melting range of an alloy, and interacts with platinum, palladium, silver, and gold to provide a heat- treating capability in gold-, silver-, and palladium-based alloys. • Copper helps to form an oxide for porcelain bonding, lowers the density slightly, and can enhance passivity in the high palladium-copper alloys.
  61. 61. 61 Gallium • Gallium is added to silver-free porcelain alloys to compensate for the decreased coefficient of thermal expansion created by the removal of silver. (Concerns over silver's potential to discolor dental porcelain have greatly limited its use in systems other than palladium-silver )
  62. 62. 62 Indium • It is a less volatile oxide-scavenging agent (to protect molten alloy) • lowers the alloy's melting range and density • added to non gold-based alloys to form an oxide layer for porcelain bonding. • enhance tarnish resistance in high silver containing alloys.
  63. 63. 63 Iron • Iron is added to some gold-based porcelain systems for hardening and oxide production. • Iron is included in a few base metal alloys as well.
  64. 64. 64 Manganese • Manganese is an oxide scavenger and a hardening agent in nickel- and cobalt-based alloys.
  65. 65. 65 Molybdenum • Molybdenum improves corrosion resistance • influences oxide production • is helpful in adjusting the coefficient of thermal expansion of nickel-based alloys.
  66. 66. 66 Nickel • Nickel has been selected as a base for porcelain alloys because its coefficient of thermal expansion approximates that of gold and it provides resistance to corrosion. • Unfortunately, nickel is a sensitizer and a known carcinogen. • Estimates of nickel sensitivity among women in the United States range from 9% to 31.9% and from 0.8% to 20.7% among men .
  67. 67. 67 Tin • Tin is a hardening agent that acts to lower the melting range of an alloy. • It also assists in oxide production for porcelain bonding in gold and palladium- based alloys. • Tin is one of the key trace elements for oxidation of the palladium-silver alloys.
  68. 68. 68 Titanium • Like aluminum and beryllium, titanium is added to lower the melting range and improve castability. • Also acts as a hardener and influences oxide formation at high temperatures.
  69. 69. 69 Zinc • lowers the melting range of an alloy • acts as a deoxidizer • Zinc improves the castability of an alloy and contributes to hardness when combined with palladium.
  70. 70. 70 Historical Perspective Of Dental Casting Alloys History of dental casting alloys has been influenced by three major factors. 1. The technological changes of dental prosthesis 2. Metallurgical advancement 3. Price changes of noble metals since 1968
  71. 71. 71 major events in the history of dental casting alloys • Introduction of lost wax technique 1907 • Replacement of Co-Cr for Au in removable partial dentures 1933 • Development of resin veneers for Au alloys 1950 • Introduction of the porcelain fused to metal technique 1959 • Palladium based alloys as alternatives to Au alloys 1968 • Ni based alloys as alternatives to Au alloys 1971 • Introduction of all ceramic technologies 1980
  72. 72. 72 Desirable Properties Of Casting Alloys 1. Bio-compatibility 2. Ease of melting & casting 3. Ease of brazing, soldering & polishing 4. Little solidification shrinkage 5. Minimal reactivity with mould material 6. Good wear resistance
  73. 73. 73 7. High strength 8. Sag resistance 9. Tarnish & corrosion resistance 10.Economic considerations 11. Lab cost
  74. 74. 74 Metal Type All-metal prostheses Metal ceramic prostheses Partial denture frameworks High Noble (HN) Au-Ag-Pd Au-Pd-Cu-Ag HN metal ceramic alloys Pure Au (99.7%) Au-Pt-Pd Au-Pd-Ag (5-12 wt % Ag) Au-Pd-Ag (>12 wt% Ag) Au-Pd Au-Ag-Cu-Pd Noble (N) Ag-Pd-Au-Cu Ag-Pd Noble metal ceramic alloys Pd-Au Pd-Au-Ag Pd-Ag Pd-Cu-Ga Pd-Ga-Ag Predominantly Base metal (PB) CP Ti Ti-Al-V Ni-Cr-Mo-Be Ni-Cr-Mo Co-Cr-Mo Co-Cr-W Cu-Al CP Ti Ti-Al-V Ni-Cr-Mo-Be Ni-Cr-Mo Co-Cr-Mo Co-Cr-W CP Ti Ti-Al-V Ni-Cr-Mo-Be Ni-Cr-Mo Co-Cr-Mo Co-Cr-W Classification of casting metals for full metal and metal ceramic prosthesis and partial dentures
  75. 75. 75 13001215base metalCo-Cr 13101250base metalNi-Cr (Cr>20 wt %) 13901330base metalNi-Cr (Cr<20 wt %) 12701160base metalNi-Cr-Be (Cr<20 wt %) 1270990NobleAg-Pd 10451185NoblePd-Ag 12301145NoblePd-Cu 1270880NobleAu-Cu-Ag-Pd 960905High nobleAu-Cu-Ag-Pd 12601160High nobleAu-Pd 11401060High NobleAu-Pt Liquidus temperature (°C) Solidus temperature (°C) ADA classificationAlloy type Solidus and liquidus temperature of the commonly used classes of alloys :
  76. 76. 76Balance0-150-1074-880-6 Noble (Ag-based) Metal Ceramic Balance-1788 High Noble (Au-based) Metal Ceramic Balance-3060- Noble (Ag-based) Metal Ceramic Balance--3852 High Noble (Au-based) Metal Ceramic Balance14452515 Noble (Ag-based) IV Balance1425456 High Noble (Au-based) IV Balance-7025- Noble (Ag-based) III Balance839646 High Noble (Ag-based) III Balance9113.575 High Noble (Au-based) III Balance714177 High Noble (Au-based) II Balance6100.583 High Noble (Au-based) I Ga, In, and ZnCuAgPdAu Elemental composition (wt%) ClassificationAlloy type Typical compositions of Casting Alloys for Full-Metal, Resin-Veneered and Metal- Ceramic Prostheses
  78. 78. 78 GOLD AND GOLD BASED ALLOYS Type Au% Ag% Cu% Pt/Pd% Zn% I (soft) 85 11 3 - 1 II(Medium) 75 12 10 2 1 III (Hard) 70 14 10 5 1 IV (Extra hard) 65 13 15 6 1
  79. 79. 79 uses 1) Type I : for low stress inlays . 2) Type 2 : are the most widely used metals for inlays. 3) Type 3 : are used when there is less support from tooth structure and when the opposing stress are high like for crowns, bridges. 4) Type 4 : are used exclusively for construction of components of partial dentures and for this reason are referred to as partial denture casting alloys.
  80. 80. 80 Karat Karat value represents the number of parts by weight of gold per 24 parts of gold. Fineness Fineness indicate the number of part per thousand parts of gold.
  81. 81. 81 IV Corrosion resistance Proportional limitType I II III Hardness Strength Ductility INCREASES DOWNWARDS DECREASES DOWNWARDS Comparative properties;
  82. 82. 82 Mechanical Property Requirements in ANSI/ADA Specification No.5 for Dental Casting Alloys (1997) 310450-300Type 4 -12--240Type 3 -12-240180Type 2 -18-18080Type 1 Minimum (%) Minimum (%) Minimum (MPa) Maximum (MPa) Minimum (MPa) HardenedAnnealedHardenedAnnealed ElongationYield strength (0.2% offset) Alloy type
  83. 83. 83 The classification based on the color of the alloy 1. Yellow gold – Those with more than 60% Au 2. Low gold or economy gold – With 42-55% Au, also has yellow color 3. White gold – are those with gold more than 50%, but palladium gives the white color 4. Silver palladium with or without gold but mainly silver – Has white color 5. Palladium silver with mainly palladium gives white color.
  84. 84. 84 Japanese gold Also known as technique alloy used for training students in casting technology - has yellow color.  composition Cu - 53% Zn - 37% Al - 7% Others - 3%
  85. 85. 85 Grain refined alloys • The grain refined alloys are those that contain iridium or ruthenium in 100-150 parts per million. • The advantages of the refined alloys are : High yield strength High elongation Homogenous casting More resistance to corrosion
  86. 86. 86 HEAT TREATMENT OF GOLD ALLOYS  Softening heat treatment : • the alloy is heated in an electric furnace at a temperature of above 700°C for 10 min and then quenched rapidly in water. • The ductility and the corrosion resistance increase whereas the strength, hardness and the proportional limit decrease.  Homogenization heat treatment : • This is done when platinum and palladium are present, to remove coring. This involves heating to 700°C for ten minutes, followed by quenching.
  87. 87. 87  Stress relief anneal : – This is done when any adjustments are done to the appliance to remove the stresses. This involves heating in a low temperature to remove the stresses for a given period of time.  Hardening heat treatment : – This is done for type III and type IV alloys which contain sufficient amount of copper. This is due to solid state transformations. The casting is heated to above 450° C and allowed to cool slowly until 200°C, then quenching. This takes about 20 min.
  88. 88. 88 LOW GOLD CONTENT ALLOYS :  SILVER - PALLADIUM ALLOYS • Contains predominantly silver • Palladium upto 25% • May or may not contain gold and copper • Traces of zinc and indium  High casting temp  Low density  Good tarnish and corrosion resistance  Properties similar to type III and type IV gold.  ALUMINIUM BRONZE ALLOYS • Cu 81-88 wt% • Al 7-11 wt% • Ni 2-4 wt% • Fe 1-4 wt%
  89. 89. 89 Alloys for Metal Ceramic Restoration Definition Partial crown, full crown or fixed partial denture made with a metal substrate to which porcelain is bonded for esthetic enhancement via an intermediate metal oxide layer
  90. 90. 90 Property Requirements of metal ceramic alloys : • Fusion temperature should be 100°C greater than the fusion temperature of porcelain. • Contact angle between the ceramic and metal should be less than 60° • Should form oxides on the surface for bonding to porcelain. -Tin, Indium and Iron are added. • should have compatible co-efficient of thermal expansion(0.5 x 10-6 /°C). - Palladium • Adequate stiffness and strength • High sag resistance • Lab workability and Casting Accuracy – in order to provide clinically acceptable castings
  91. 91.
  92. 92.
  93. 93. 93 High Noble Alloys Gold-Platinum-Palladium Alloys Composition : • Gold: 75%-88% • Platinum: up to 8% • Palladium: up to 11 % • Silver: up to 5% (if present) • Trace elements like indium, iron, and tin for porcelain bonding. (If the palladium content exceeds that of platinum, then the alloys should be classified as Au-Pd-Pt.)
  94. 94. 94 Advantages • Excellent castability • Excellent porcelain bonding • Easy to adjust and finish • Excellent corrosion and tarnish resistance • Burnishable Disadvantages • High cost • Poor sag resistance • Low hardness (greater wear) • High density (fewer castings per ounce)
  95. 95. 95 Gold-Palladium-Silver Alloys Introduced in 1970 as will ceram w  composition - • Gold: 39%-53% • Palladium:25%-35% • Silver: 12%-22% • Tin ,Indium & Ruthenium  Advantages • Less expensive than Au-Pt-Pd alloys • Improved rigidity and sag resistance  Disadvantages • High coefficient of thermal expansion • Tarnish and corrosion resistant
  96. 96. 96 Gold-Palladium alloys  Composition • Gold – 44% -55% • Palladium – 35% - 45% • Gallium up to 5% • Iridium and tin up to 8% - 12%  Advantages • Excellent castability • Good bond strength & sag resistance • Tarnish and corrosion resistant • Lower density  Disadvantages • High cost • Not thermally compatible with high expansion dental porcelains
  97. 97. 97 Palladium-Silver alloys  Composition • Palladium – 55% - 60% • Silver – 28% - 30% • Indium and tin AdvantagesAdvantages • Good castabilityGood castability • Good porcelain bondingGood porcelain bonding • Excellent sag resistanceExcellent sag resistance • Low HardnessLow Hardness • BurnishabilityBurnishability • Good tarnish and corrosionGood tarnish and corrosion •Low densityLow density • Low costLow cost • Moderate nobility levelModerate nobility level • Suitable for long-span fixedSuitable for long-span fixed partial denturespartial dentures Noble Metal
  98. 98. 98 Disadvantages •High coefficient of thermalHigh coefficient of thermal expansionexpansion •Discoloration (yellow, brown,Discoloration (yellow, brown, or green) may occur with someor green) may occur with some dental porcelainsdental porcelains •Some castability problemsSome castability problems •Pd and Ag prone to absorbPd and Ag prone to absorb gasesgases •Require regular purging ofRequire regular purging of the porcelain furnacethe porcelain furnace •May form internal oxidesMay form internal oxides •Should not be cast in aShould not be cast in a carbon cruciblecarbon crucible •Non carbon phosphateNon carbon phosphate bonded investmentsbonded investments recommendedrecommended
  99. 99. 99 Palladium-cobalt alloys Composition • Palladium: 78%-88% • Cobalt: 4%-10% Advantages • Low cost • good sag resistance • Low density • Good polishability • easier to presolder than high Pd-Cu alloys Disadvantage • Produce a thick, dark oxide which may cause bluing of porcelain • Prone to gas absorption • Little information on long-term clinical
  100. 100. 100 High Palladium-Silver-Gold alloys  Composition • Palladium: 75%-86% • Silver: less than 1 %-7% • Gold: 2%-6% • Platinum: less than 1.0% (if present)  Advantages • Improved sag resistance • Light-colored oxide layer  Disadvantages • A relatively new alloy group • No data on long-term performance • Like other palladium-based alloys are prone to gaseous absorption • Should not be cast in carbon crucibles
  101. 101. 101 Palladium-Copper alloys Composition • Palladium: 70%-80% • Copper: 9%-15% • Gold: 1 %-2% (if present) • Platinum: 1 % (if present) Disadvantages • Produce dark, thick oxides May discolor (gray) some dental porcelains • Should not be cast in carbon crucibles • Prone to gaseous absorption
  102. 102. 102 Pd-Ga-Ag & Pd-Ga-Ag-Au Alloys • These are the most resistant of the noble alloys. • These were introduced because of their tendency to form lighter oxides than Pd-Cu or Pd-Co. • They are compatible with lower expansion porcelains like vita porcelain.
  103. 103. 103 PHYSICAL PROPERTIES OF HIGH NOBLE AND NOBLE METAL ALLOYS • All are biocompatible • Good resistance to tarnish and corrosion • Melting temperature of around 1000°C. • Density of 15gm/cm3 . • Hardness from soft to hard • Elongation which is a measure of ductility of about 20-39% • Linear coefficient of thermal expansion in the range of 14 – 18 x 10 -6 /°C. • Yield strength in the range of 103 – 572 MPa.
  104. 104. 104 BASE METAL ALLOYS  According to the ADA the following combinations are available : 1. Cobalt – chromium 2. Nickel – chromium 3. Nickel – chromium – beryllium 4. Nickel – cobalt – chromium 5. Titanium – aluminium – vanadium
  105. 105. 105 Nickel-chromium-beryllium alloys  Composition • Nickel: 62%-82% • Chromium: 11 %-20% • Beryllium: up to 2.0% • Also includes: aluminum carbon gallium iron manganese molybdenum silicon Titanium
  106. 106. 106 Advantages • Low cost • Low density permits more casting per ounce • High sag resistance • Can produce thin castings • Poor thermal conductor • Can be etched
  107. 107. 107  Disadvantages • Cannot use with nickel- sensitive patients • Beryllium exposure may be potentially harmful to technicians and patients • Proper melting and casting is a learned skill • Bond failure more common in the oxide layer • High hardness (may wear opposing teeth) • Difficult to solder • Difficult to cut through cemented castings The occupational health and safety administration (OSHA) specifies that exposure to Beryllium dust in air should be limited to a concentration of 2 ug /meter cube
  108. 108. 108 Nickel-chromium beryllium-free alloys  Composition • Nickel: 62%-77% • Chromium: 11 %-22% • Boron , Iron, Molybdenum, Tantalum. • May not cast as well asNi-Cr-Be alloys • Produce more oxides than Ni-Cr-Be alloys
  109. 109. 109 Cobalt-chromium alloys vitallium (1928)  TYPES • Type I -fusion temperature greater than 2400F. • Type II - fusion temperature less than 2400F. Composition • Cobalt: 53%-68% • Chromium: 25%-34% • Trace elements include molybdenum, ruthenium
  110. 110. 110 Disadvantages • More difficult to process than nickel-base alloys • High hardness (may wear the opposing dentition) • Oxidize more than both nickel-based alloys • No information on long-term clinical studies
  111. 111. 111 COMPARISON OF PROPERTIES OF THE VARIOUS TYPES OF BASE METAL ALLOYS HighHighFairExcellent Bond to porcelain ExtremelyModeratelyModerately HighMinimal Technique sensitivity GoodExcellentExcellentPoor-excellentSag resistance 103207145-22090 Elastic Modulus (GPa) (g/cm3 ) ExcellentFairExcellentExcellentBiocompatibility CPTiNi-Cr-BeCo-CrHigh noble alloyProperty
  112. 112. 112 COMPARISON OF THE PROPERTIES OF TYPE IV AND Co-Cr ALLOY : Simple adequate high Complicated adequate reasonable Heat treatment Tarnish resistance price 1.25 – 1.652.3Casting shrinkage Co-Cr require electrical induction or oxyacetylene Lower than 1000As high as 1500Melting temperature (o C) Both resist stresses without deformation. 500700Proportional limit (MPa) Co-Cr more rigid for the same thickness 100220Modulus of elasticity (GPa) Co-Cr clasps may fracture if adjustments are made. 15 (as cast) 8 (hardened) 2Ductility More flexibleStiffStiffness More difficult to polish but retains polish during services. 250 (Softer than enamel) 420 (Hard than enamel) Hardness (Vickers) More difficult to produce defect free castings for CO-Cr but dentures are lighter. 158Density (gms / Both acceptable750850Tensile Strength (Mpa) IV CommentsType GoldCo-CrProperties
  113. 113. 113 COMPARISON OF PROPERTIES OF TYPE III AND Ni-Cr ALLOY Ni-Cr more difficult to polish but retains polish during service. Burnishing is possible but high forces are required. 20 (as cast) 10 (hardened) 300 upto 30% Hardness (Vickers Ductility) Higher modulus of Ni-Cr advantage for larger restorations. 85220Modulus elasticity (GPa) Both high enough to prevent distortions when used. 290230Tensile strength (MPa) Ni-Cr alloys require electrical induction or oxyacetylene flame. Both adequate Lower than 1000 as high as 1350 Fusion temperature (oC) More difficult to produce defect free castings for Ni-Cr alloys. 158Density (gm/
  114. 114. 114 Titanium alloys • High biocompatibility • According to the American Society for Testing and Materials (ASTM), there are five unalloyed grades of CP Ti (Grades 1-4, and Grade 7), based on the concentration of • oxygen (0.18 wt% to 0.40 wt%) and • iron (0.2 wt% to 0.5 wt%). • Other impurities include nitrogen (0.03 wt% to 0.05 wt%), • carbon (0.1 m%), and hydrogen (0.015 wt%).
  115. 115. 115 • Grade 1 CP Ti is the purest and softest form • It has a moderately high tensile strength • moderately high stiffness • low density • low thermal expansion coefficient. • The elastic modulus of CP Ti is comparable to that of tooth enamel and noble alloys, but it is lower than that of other base metal alloys
  116. 116. 116 • Casting of titanium alloys is difficult due to a high casting temperature – 2000° c • Rapid oxidation and reactions with investments • Melting is done in specially designed furnaces with an argon atmosphere • Ti-6Al-4v has been used for PFM restorations • Used with low expansions porcelains
  117. 117. 117 SINTERED COMPOSITE • These composites consist of sintered high noble alloy sponge infiltrated with an almost pure gold alloy. • The result is a composite between the two gold alloys that is not cast, but fired onto a refractory die. • The porcelain does not bond through an oxide layer in these systems, but it bonds mechanically to a micro rough surface. • The advantages of this that any stress concentration on the ceramic is relieved by the excellent ductility of the metal
  118. 118. 118 CONCLUSION  Finally the guidelines for the selection of an alloy for a restoration should be based on : 1. A thorough understanding of the alloy 2. Avoid selecting an alloy based on its color unless all other factors are equal 3. Know the complete composition of alloys, and avoid elements that are allergic to the patient 4. Whenever possible use single phase alloys
  119. 119. 119 5. Using clinically proven products from quality manufacturers 6. Use alloy that have been tested for elemental release and corrosion and have the lowest possible release of elements. 7. Focus on long term clinical performance 8. Finally it is important for the dentist to remember and take up the responsibility of being responsible for the safety and efficacy of any restoration.
  120. 120. 120 Thank you For more details please visit