Precious metal alloys in dentistry


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Precious metal alloys in dentistry

  1. 1. Vinay Pavankumar .K 1ST Year P.G Department of Prosthodontics AECS Maaruti Dental College
  2. 2. Precious metal alloys Classification Composition Properties History Alloy Treatment of noble and high noble alloys
  3. 3. 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. Two or more metals that are mutually soluble in each other in the molten state.
  4. 4. Noble metal  Those metal elements that resist oxidation, tarnish, and corrosion during heating, casting, or soldering and when used intraorally; examples include gold and platinum. Good metallic surface that retain their surface in dry air. Eight noble metals Metallurgists consider silver a noble metal, but it is not considered a noble metal in dentistry
  5. 5. Precious metal alloy Precious metal: a metal containing primarily elements of the platinum group, gold, and silver. Precious metal alloy: an alloy predominantly composed of elements considered precious, i.e., gold, the six metals of the platinum group (platinum, osmium, iridium, palladium, ruthenium, and rhodium), and silver Term precious stems from the trading of these metals on the commodities market
  6. 6. HISTORICAL PERSPECTIVE ON PRECIOUS METAL & ALLOYS IN DENTISTRY C. Spence Bate at the 1883,annual meeting of the British Dental Association, in Plymouth, entitled `A Review of the Scientific Progress of Dental Surgery from 1771 to 1883, contains the passage: “We must congratulate ourselves on the great improvement that has taken place in the power of retaining diseased teeth and restoring to usefulness such as would, a few years ago, have been considered hopelessly irrecoverable. The extent of this process of repair can best be understood by saying that, independent of amalgam and cement stoppings, 20 000 ounces [620 kg] of fine gold is annually used in filling teeth ...”
  7. 7. As early as the seventh centry B.C Etruscan dental prostheses made by passing thin strips of gold round teeth on each side of a space from which a tooth or teeth had been lost and rivetting the strip so as to hold the substitute teeth in place.
  8. 8.  The discoveries were dated back to 550 B.C . A canine tooth like object made of two piece of calcite having hardness similar to natural teeth showing wear on the chewing surface & secured with gold wires wrapped around the neck of adjacent teeth
  9. 9.  The first printed book on dentistry, entitled 'ArtzneyBuchlein' ('The Little Pharmacopaeia'), was published by Michael Blum in Leipzig in 1530. Under this title or as 'Zene Artznei' ('Dental Medicine') “Scrape and clean the hole and the area of decay with a fine small chisel or a little knife or a file, or with another suitable instrument, and then to preserve the other part of the tooth, fill the cavity with gold leaves.”
  10. 10.  Maggilio in 1809 , a dentist at the university of Nancy , France, author of the book called “THE ART OF THE DENTIST”. The first reference to modern style implants. He has described the implant & placement. He made the tooth root shaped implant with 18 carat gold with three prongs at the end to hold it in place in the bone . The implant was placed in the freshly extracted socket site retained with the prongs. After the tissues healed the crown was attached with the help of post placed into the hole of root section of the implant. He placed the single stage gold implant.
  11. 11. In 1886 Harris treated a Chinese patient in Grass valley , California . He placed the tooth root shaped platinum post with lead coating, lasted for 27 yrs Reported in Dental Comos. In 1888, Charles Henry Land who fused porcelain on thin platinum caps for use as crowns. This technique is still used in making jacket crowns.  In 1890, a Massachusetts minister had his lower jaw resected & was restored with an extensive system of gold crowns soldered & joined to hinged device attached to the remaining dentition
  12. 12.  Bonwill in 1895 reported on the implantation of one or two tubes of gold or Iridium as a support for individual teeth or crown.  In 1898 R. E Payne at the National Dental Association meeting gave the first clinical demonstration by placing the silver capsule in the extracted tooth socket.  In 1896 B. F.Philbrook, attempted to make soft, fusible metal inlays by a lost wax process, he fitted several white metal inlays and one gold inlay.
  13. 13. In 1897 George B. Martin demonstrated gold dummy or artificial teeth, called `pontics', for use on fixed bridges; these were soldered to gold crowns on the abutment teeth. In 1900, J. G.Schottler used a method to restore the biting edges of front teeth by placing a platinum wire in the root canal, building the required shape on the tooth with wax. Invested and casted it in gold. In 1906 John A. Lenz obtained a patent for devising a method for lost wax casting a gold chewing surface onto a gold band made to fit around a tooth.
  14. 14. At a meeting of the New York Odontological Society on January 15, 1907, William H.Taggart of Chicago read a lecture entitled `A New and Accurate Method of Casting Gold Inlays' in which he described a lost wax technique which can truly be said to have revolutionized restorative and prosthetic dentistry
  15. 15.  In 1907, a Dr. Solbrig, in Paris. introduced his casting pliers which achieved enormous popularity for the rapid production of small inlays.  In 1913 Dr. Edward J. Greenfield, fabricated the hollow cylindrical basket root of 20 gauge iridioplatinum soldered with 24 carat gold.  The recent development of gold abutment retainaing screws and cylinder.
  16. 16. Gold Soft, rich yellow color and a strong metallic luster Most malleable and ductile 0.2% lead – brittle Soluble in aqua regia Alloyed with copper, silver, platinum – increases hardness , durability and elasticity
  17. 17. Platinum  Bluish white metal  Hardness similar to copper  Higher melting point ( 1772°C) than porcelain  Coefficient of thermal expansion close to porcelain  Lighten the color of yellow gold based alloys  Common constituent in precision prosthetic attachments
  18. 18. Silver (Ag) Malleable, ductile; white metal. Stronger and harder than gold, softer than copper. Absorbs oxygen in molten state-difficult to cast Forms series of solid solutions with palladium and gold .  Neutralizes reddish color of alloys containing copper
  19. 19. Palladium (Pd)  White metal darker than platinum  Density little more than half that of Pt and Au  Absorbs hydrogen gas when heated  Not used in pure state in dentistry  Whitens yellow gold based alloys.
  20. 20. Iridium(Ir ) Ruthenium(Ru ), Rhodium(Rh) & Osmium(Os) Grain refiners Improves mechanical properties and uniformity of properties within alloy Extremely high melting point of Ir - 2410°C and Ru - 2310°C – serve as nucleating centers Osmium(Os) has a very high melting point, and is very expensive, hence not used in dentistry.
  21. 21. Physical properties of noble and precious metals
  22. 22. Mechanical properties of noble and precious metals
  23. 23. History of Dental casting alloy  1907 : Lost wax process technique -W H Taggart.  1932 : Classification of gold based casting alloys.  1933 : Introduction of Co-Cr and Ni-Cr alloys.  1959 : Porcelain-fused to metal prothesis.  1971 : End of Bretton Woods system.  1976 : The medical and dental devices act.  1996 : European medical devices directive.  1998 : The clean air act.
  24. 24. Classification of dental casting alloys: According to their use: All metal inlays Crowns and bridges Metal ceramic prothesis Post and cores Removable partial dentures. Implants According to major elements : •Gold based •Palladium based •Silver based •Nickel based •Cobalt based •Titanium based According Dominant Phase system: • Single • Eutectic • Peritectic • Intermetallic
  25. 25. Alloy Classification by Noble Metal Content Alloy type Total noble metal content High noble (HN) Contain ≥40 wt% Au and ≥60 wt% of noble metal elements (Au, Pt, Pd, Rh , Ru, Ir, Os) Noble (N) Contain ≥25 wt% of noble metal elements Predominantly Base metal (PB) Contain <25wt% of noble metal elements
  26. 26. In 2003, the Council for Scientific Affairs revised the classification to include titanium in a separate category because of its extensive usage and similar properties with noble metals class Required noble content (%) Required gold content (%) Required titanium content (%) High noble alloys ≥60 ≥40 Titanium and titanium alloys ≥85 Noble alloys ≥25 Predominantly base metals ≥25 Givan A A, Precious Metals in Dentistry, Dent Clin N Am vol 51 2007;591-601
  27. 27. Classification of Mettallic Materials for Dental Application ISO 22674 (2006) Type Yield Strength (Mpa) Elongation (%) Examples of Application 0 -- -- Single fixed tooth fixed restorations 1 80 18 Single fixed tooth fixed restorations veneered or non veneered 2 180 10 For Single fixed tooth fixed restorations 3 270 5 For multiple unit fixed restorations 4 360 2 For appliances with this cross sections that are subject to very high forces 5 500 2 For thin removable partial dentures, parts with thin cross sections
  28. 28. According to yield strength and percentage elongation (proposed in ISO draft international standard 1562 for casting gold alloys 2002) Alloy type Hardness Yield strength (MPa) Percent elongation % Type 1: Low strength Soft 80 18 Type 2:Medium strength Medium 180 10 Type 3: high strength Hard 270 5 Type 4: Extra-high strength Extra hard 360 3
  29. 29. Classification of casting metals for full metal, Metal Ceramic and Partial Dentures Metal type All metal Metal Ceramic Partial Denture High noble Au-Ag-Pd Au-Pd-Cu-Ag Au-Pt-Pd Au-Pd-Ag (5-12 wt% Ag) Au-Pd-Ag (>12 wt% Ag) Au-Pd Au-Ag-Cu-Pd Noble Ag-Pd-Au-Cu Ag-Pd Pd-Au Pd-Au-Ag Pd-Ag Pd-Cu-Ga Pd-Ga-Ag
  30. 30. Desirable properties of casting alloys Biocompatibility Tarnish and Corrosion resistance Compatible thermal properties Castability Aesthetics Economical
  31. 31. Functional Mechanical Properties of Casting alloys  Elastic modulus Yield strength Ductility Hardness Fatigue Resistance
  32. 32. Selected properties of major types of high-noble alloys Alloy type Solidus- liquidus (C) Color Phase structure Elastic modulus (staticGPa) Vicker’s hardness (kg/mm2) Yield strength (tension, 0.2%, Mpa) Au-Pt (Zn) 1060– 1140 Yellow Multiple 65–96 165–210 360–580 Au-Pd (Ag) 1160– 1260 White Single 105 280 385 Au-Cu-Ag 905–960 White Single 100 210 450
  33. 33. Mechanical properties of noble and precious metal casting alloys
  34. 34.  Treatment of noble and high noble alloys  Type lll and type lV gold alloys can be hardened and softened.  Softening heat treatment/homogenizing-Solution heat treatment.  Hardening heat treatment-Age hardening.
  35. 35. Softening Heat Treatment  Increases ductility  reduces tensile strength ,proportional limit and hardness Method:  Casting placed in electric furnace  10 minutes,700°Cquenched in water resulting disordered solid solution  Indicated-alloys that are to be ground, shaped or otherwise cold worked either in or out of mouth.
  36. 36. Hardening of Noble metals Increases strength, proportional limit, and hardness, but decreases ductility If positioning of two elements become ordered-ordered solution Copper present in gold alloy helps in this process. Method: Soaking/ageing casting-15 to 30 minutes before water quenching 200°C to 450°C Ideally, before age hardening it should first be subjected to softening heat treatment
  37. 37. Alloys for metal ceramic prosthesis Classification of Noble PFM alloys Au Based Pd Based Au-Pt-Pd (21 K) Pd-Ag Au- Pd (13 K) Pd-Cu Au-Pd-Ag (13 K) Pd-Co
  38. 38. Noble alloys  Gold-copper-silver- palladium  Palladium-copper-gallium  Palladium-silver and silver- palladium High noble alloys  Gold-Platinum alloy  Gold-Palladium alloy  Gold-copper-silver-palladium alloys
  39. 39. Physical and Chemical properties 1. Noble metal content 2. Hardness 3. Yield strength 4. Elongation 5. Fusion temperature 6. Porcelain-Metal Compatibility 7. Color stability 8. Biocompatibility
  40. 40. Typical properties of alloys for PFM restorations
  41. 41. High noble alloys  Minimum of 60% noble metals (any combination of gold, palladium and silver) with a minimum of 40% by weight of gold.  Tin, indium and/or iron oxide layer formation chemical bond for the porcelain.
  42. 42. Gold-platinum alloy Developed alternative to palladium alloys For full cast as well as metal-ceramic restorations.  More prone to sagging, they should be limited to short span bridges.  A typical composition is Gold 85%;  Platinum12%;  Zinc 1%;  Silver (in few brands)
  43. 43. Gold-palladium alloy Used for full cast /metal-ceramic restorations. Palladium - high melting temperature - impart a white or gray color - improves sag resistance  These alloys usually contain indium, tin or gallium to promote an oxide layer. A typical composition  Gold 52%;  Palladium 38%;  Indium 8.5%;  Silver (in some brands).
  44. 44. Gold-copper-silver-palladium alloy  Have low melting temperature  Not used for metal-ceramic applications.  Greening of porcelain – due to silver  Copper tends to cause sagging during porcelain processing. A typical composition is  Gold 72%,  Copper 10%;  Silver 14%;  Palladium 3%.
  45. 45. Noble alloys  Contain at least 25% by weight of noble metal (gold, palladium or silver)  Have relatively high-strength, durability, hardness, ductility.  They may be yellow or white in color.
  46. 46. Gold–copper-silver-palladium alloy  More copper and silver  Have a fairly low melting temperature  More prone to sagging during application of porcelain.  Used mostly for full cast restorations rather than PFM applications.  A typical formula is: gold 45%  Copper 15%  Silver 25%  Palladium 5%
  47. 47. Palladium-copper-gallium alloys  Introduced in 1983  Very rigid excellent full cast or PFM restorations.  Contain copper  prone to sagging during porcelain firing.  Gallium  reduces the melting temperature A typical composition is  Palladium 79%  Copper 7%;  Gallium 6%  Hardness is comparable to base metal alloy but are not burnishable
  48. 48. Palladium-silver and silver-palladium alloys  Higher palladium alloys - PFM frameworks.  Higher silver alloys - susceptible to corrosion - greening of porcelain  High resistance to sagging  very rigid - good for long spans
  49. 49.  More castable (more fluid in the molten state)  Easier to solder and easier to work with than the base metal alloys.  Typical composition for Palladium- silver alloy:  Palladium 61%; silver 24%; Tin (in some) Silver-palladium alloy:  Silver 66%; Palladium 23%; gold (in some formulation)
  50. 50. Greening  Discoloration of porcelain  Due to silver ions  Mechanism not clear  Cervical region  Metal - ceramic interface  Prevented -silver free alloys  metal coating agents
  51. 51. Precious metals & dental implants GOLD UCLA-TYPE ABUTMENTS • 64% gold, 22% palladium • Melting range 2400˚F-2500˚F (1320˚C-1370˚C) • Gold alloy abutment screw retention increases the preloading force there by assuring precision fit to implant Ceraone & Mirus cone abutments • SEMI-BURNOUT CYLINDER Non-oxidizing, high precious gold platinum alloy with a plastic wax-up sleeve Cylinder base Alloy Melting range Coefficient of thermal linear expansion Plastic sleeve Burnout temperature Au 60%, Pt 24%, Pd 15%, Ir 1% 1400–1460°C/ 2552-2660°F 25–500°C 12.3 (10–6K-1) 25–600°C 12.7 (10–6K-1 700°C/1292°F
  52. 52. Review of literature  The study evaluated the cervical and internal fit of complete metal crowns that were cast and recast using palladium-silver alloy and 3 different marginal configurations used were straight shoulder, 20-degree bevel shoulder, and 45-degree chamfer.  Results showed - The new alloy provided significantly better adaptation than the recast alloy for both marginal and internal discrepancy measurements. Marginal designs did not shown any statistical differences when the new metal was used Lopes,S.Consani et al ,Influence of recasting palladium-silver alloy on the fit of crowns with different marginal configurations J Prosthet dent,2005;94,5:430-434
  53. 53. • This study evaluated the influence of a composite interlayer (at the metal–ceramic interface) on the shear bond strength of a metal–ceramic composite when compared with a conventional porcelain fused to metal (PFM). The shear bond strength results for all composites bonded to metal and to ceramic substrates were significantly higher (>150 MPa) than those registered in the upper range of conventional porcelain fused to metal (PFM) techniques (∼80 MPa). The use of a composite interlayer proved to enhance metal/ceramic adhesion in 160%. B. Henriques et al. Optimization of bond strength between gold alloy and porcelain through a composite interlayer obtained by powder metallurgy .Materials Science and Engineering A 528 (2011) 1415–1420
  54. 54. The aim of this study were to investigate the fatigue limits of two Pd– Ag alloys (Ivoclar Vivadent) with differing mechanical properties and varying proportions of secondary alloying elements, examine the effect of casting porosity on fatigue behavior,and determine the effect of casting size on microstructures and Vickers hardness Tension test bars, heat-treated to simulate dental porcelain application, were subjected to cyclic loading at 10 Hz, with R-ratio of −1 for amplitudes of compressive and tensile stress. Two replicate specimens were tested at each stress amplitude. Fracture surfaces were examined with a scanning electron microscope (SEM). Sectioned fatigue specimens and additional cast specimens simulating copings for a maxillary central incisor restoration were also examined with the SEM, and Vickers hardness was measured using 1 kg load. Casting porosity was evaluated in sectioned fatigue fracture specimens, using an image analysis program. •Baba.D.Li.N etal, Study of Pd–Ag dental alloys: examination of effect of casting porosity on fatigue behavior and microstructural analysis Journal of Materials Science: Materials in Medicine October 2010, Volume 21, Issue 10, pp 2723-2731
  55. 55. relatively low ratios of fatigue limit to 0.2% yield strength are similar to those found previously for high-palladium dental alloys, and are attributed to their complex microstructures and casting porosity. Complex fatigue fracture surfaces with striations were observed forboth alloys. Substantial further decrease in the number of cycles for fatigue failure only occurred when the pore size and volume percentage became excessive. While the heat-treated alloys had equiaxed grains with precipitates, the microstructural homogenization resulting from simulated porcelain firing differed considerably for the coping and fatigue test specimens; the latter specimens had significantly higher values of Vickers hardness. •Baba.D.Li.N etal, Study of Pd–Ag dental alloys: examination of effect of casting porosity on fatigue behavior and microstructural analysis Journal of Materials Science: Materials in Medicine October 2010, Volume 21, Issue 10, pp 2723-2731
  56. 56. CONCLUSION
  57. 57. References Anusavice, Phillips Science of Dental Materials, 12th edition, 2012, Elsevier publications, Florida, Pp 69-91, pp 367- 384 John F. McCabe & Angus W.G. Walls, Applied Dental Materials, 9th edition, 2008, Blackwell science publications, United kingdom, Pp 62-70 Craig G.R. Powers J.M., Restorative Dental Materials, 12th edition,2006, Elsevier publications, USA, Pp 359-37 O’Brien W.J., Dental materials and their selection, 3rd edition, 2002, Quintessence publications, Canada, pp 65-74, pp 192-200
  58. 58.  J.L. Ferracane, Materials in Dentistry, 2nd edition, 2001, Susan Katz publishers, USA, Pp 281-286  Donaldson.J.A, The Use of Gold in Dentistry,AN HISTORICAL OVERVIEW. PART I,GoldBull 1980;13(3):117-24; (4),160-5  Givan A A, Precious Metals in Dentistry, Dent Clin N Am vol 51 2007;591-601  Wataha J C, Alloys for prosthodontic restorations, J Prosthet Dent 2002;87:351-63  Wataha J C, Casting alloys, Dent Clin N Am 48 (2004) 499–512
  59. 59.  Lopes,Consani S et al, Influence of recasting palladium-silver alloy on the fit of crowns with different marginal configurations, J Prosthet dent;94,5:430-434  B. Henriques et al. Optimization of bond strength between gold alloy and porcelain through a composite interlayer obtained by powder metallurgy .Materials Science and Engineering A 528 (2011) 1415– 1420  Roach.M.D,Williamson R.S, Thomas J.A. Noble and Precious Metal Applications in Biomaterials with Emphasis on Dentistry ASM Handbook, 2012, Volume 23, Materials for Medical Devices. Pp 251-262  Helmut.K, Mirza.N, Manfred.S,Dental Gold Alloys composition, properties and applications Gold Bull,1981, 14, (2) 57-64