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Dental Amalgam

Dental Amalgam. Col Kraig S. Vandewalle USAF Dental Evaluation & Consultation Service. Official Disclaimer. The opinions expressed in this presentation are those of the author and do not necessarily reflect the official position of the US Air Force or the Department of Defense (DOD)

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Dental Amalgam

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  1. Dental Amalgam Col Kraig S. Vandewalle USAF Dental Evaluation & Consultation Service

  2. Official Disclaimer • The opinions expressed in this presentation are those of the author and do not necessarily reflect the official position of the US Air Force or the Department of Defense (DOD) • Devices or materials appearing in this presentation are used as examples of currently available products/technologies and do not imply an endorsement by the author and/or the USAF/DOD

  3. Overview • History • Basic composition • Basic setting reactions • Classifications • Manufacturing • Variables in amalgam performance Click here for briefing on dental amalgam (PDF)

  4. History • 1833 • Crawcour brothers introduceamalgam to US • powdered silver coins mixed with mercury • expanded on setting • 1895 • G.V. Black develops formula for modern amalgam alloy • 67% silver, 27% tin, 5% copper, 1% zinc • overcame expansion problems

  5. History • 1960’s • conventional low-copper lathe-cut alloys • smaller particles • first generation high-copper alloys • Dispersalloy (Caulk) • admixture of spherical Ag-Cueutectic particles with conventional lathe-cut • eliminated gamma-2 phase Mahler J Dent Res 1997

  6. History • 1970’s • first single composition spherical • Tytin (Kerr) • ternary system (silver/tin/copper) • 1980’s • alloys similar to Dispersalloy and Tytin • 1990’s • mercury-free alloys Mahler J Dent Res 1997

  7. Amalgam • An alloy of mercury with another metal.

  8. Why Amalgam? • Inexpensive • Ease of use • Proven track record • >100 years • Familiarity • Resin-free • less allergies than composite Click here for Talking Paper on Amalgam Safety (PDF)

  9. Constituents in Amalgam • Basic • Silver • Tin • Copper • Mercury • Other • Zinc • Indium • Palladium

  10. Basic Constituents • Silver (Ag) • increases strength • increases expansion • Tin (Sn) • decreases expansion • decreased strength • increases setting time Phillip’s Science of Dental Materials 2003

  11. Basic Constituents • Copper (Cu) • ties up tin • reducing gamma-2 formation • increases strength • reduces tarnish and corrosion • reduces creep • reduces marginal deterioration Phillip’s Science of Dental Materials 2003

  12. Basic Constituents • Mercury (Hg) • activates reaction • only pure metal that is liquid at room temperature • spherical alloys • require less mercury • smaller surface area easier to wet • 40 to 45% Hg • admixed alloys • require more mercury • lathe-cut particles more difficult to wet • 45 to 50% Hg Click here for ADA Mercury Hygiene Recommendations Phillip’s Science of Dental Materials 2003

  13. Þ H2O + Zn ZnO + H2 Other Constituents • Zinc (Zn) • used in manufacturing • decreases oxidation of other elements • sacrificial anode • provides better clinical performance • less marginal breakdown • Osborne JW Am J Dent 1992 • causes delayed expansion with low Cu alloys • if contaminated with moisture during condensation • Phillips RW JADA 1954 Phillip’s Science of Dental Materials 2003

  14. Other Constituents • Indium (In) • decreases surface tension • reduces amount of mercury necessary • reduces emitted mercury vapor • reduces creep and marginal breakdown • increases strength • must be used in admixed alloys • example • Indisperse (Indisperse Distributing Company) • 5% indium Powell J Dent Res 1989

  15. Other Constituents • Palladium (Pd) • reduced corrosion • greater luster • example • Valiant PhD (Ivoclar Vivadent) • 0.5% palladium Mahler J Dent Res 1990

  16. Basic Composition • A silver-mercury matrix containing filler particles of silver-tin • Filler (bricks) • Ag3Sn called gamma • can be in various shapes • irregular (lathe-cut), spherical,or a combination • Matrix • Ag2Hg3 called gamma 1 • cement • Sn8Hgcalled gamma 2 • voids Phillip’s Science of Dental Materials 2003

  17. Basic Setting Reactions • Conventional low-copper alloys • Admixed high-copper alloys • Single composition high-copper alloys

  18. Ag3Sn + HgÞAg3Sn + Ag2Hg3 + Sn8Hg   1 2 Phillip’s Science of Dental Materials 2003 Conventional Low-Copper Alloys • Dissolution and precipitation • Hg dissolves Ag and Snfrom alloy • Intermetallic compoundsformed Ag-Sn Alloy Hg Hg Ag Sn Ag Ag Sn Sn Ag-Sn Alloy Ag-Sn Alloy Mercury (Hg)

  19. Ag3Sn + HgÞAg3Sn + Ag2Hg3 + Sn8Hg   1 2 Phillip’s Science of Dental Materials 2003 Conventional Low-Copper Alloys • Gamma () = Ag3Sn • unreacted alloy • strongest phase and corrodes the least • forms 30% of volume of set amalgam Hg Ag-Sn Alloy Hg Hg Ag Sn Ag Ag Sn Sn Ag-Sn Alloy Ag-Sn Alloy Mercury

  20. Ag3Sn + HgÞAg3Sn + Ag2Hg3 + Sn8Hg   1 2 Phillip’s Science of Dental Materials 2003 Conventional Low-Copper Alloys • Gamma 1 (1) = Ag2Hg3 • matrix for unreacted alloyand 2nd strongest phase • 10 micron grainsbinding gamma () • 60% of volume Ag-Sn Alloy 1 Ag-Sn Alloy Ag-Sn Alloy

  21. Ag-Sn Alloy Ag-Sn Alloy Ag-Sn Alloy 2 Ag3Sn + HgÞAg3Sn + Ag2Hg3 + Sn8Hg   1 2 Phillip’s Science of Dental Materials 2003 Conventional Low-Copper Alloys • Gamma 2 (2) = Sn8Hg • weakest and softest phase • corrodes fast, voids form • corrosion yields Hg which reacts with more gamma () • 10% of volume • volume decreases with time due to corrosion

  22. Ag-Cu Alloy Hg Hg Ag Ag Ag Ag Sn Sn Ag-Sn Alloy Ag-Sn Alloy Mercury Admixed High-Copper Alloys • Ag enters Hg from Ag-Cu spherical eutectic particles • eutectic • an alloy in which the elements are completely soluble in liquid solution but separate into distinct areas upon solidification • Both Ag and Sn enter Hg from Ag3Sn particles • Ag3Sn + Ag-Cu + HgÞAg3Sn + Ag-Cu + Ag2Hg3 + Cu6Sn5   1  Phillip’s Science of Dental Materials 2003

  23. Ag-Cu Alloy Ag-Sn Alloy Ag-Sn Alloy Admixed High-Copper Alloys • Sn diffuses to surface of Ag-Cu particles • reacts with Cu to form (eta)Cu6Sn5 () • around unconsumedAg-Cu particles • Ag3Sn + Ag-Cu + HgÞAg3Sn + Ag-Cu + Ag2Hg3 + Cu6Sn5   1  Phillip’s Science of Dental Materials 2003

  24. Admixed High-Copper Alloys • Gamma 1 (1) (Ag2Hg3) surrounds () eta phase (Cu6Sn5) and gamma ()alloy particles (Ag3Sn)  Ag-Cu Alloy Ag-Sn Alloy Ag-Sn Alloy 1 • Ag3Sn + Ag-Cu + HgÞAg3Sn + Ag-Cu + Ag2Hg3 + Cu6Sn5   1  Phillip’s Science of Dental Materials 2003

  25. Ag-Sn Alloy Ag-Sn Alloy Ag-Sn Alloy • Ag3Sn + Cu3Sn + HgÞAg3Sn + Cu3Sn + Ag2Hg3 + Cu6Sn5     1  Phillip’s Science of Dental Materials 2003 Single Composition High-Copper Alloys • Gamma sphere () (Ag3Sn) with epsilon coating ()(Cu3Sn) • Ag and Sn dissolve in Hg  Ag Sn Sn Ag Mercury (Hg)

  26. Ag-Sn Alloy Ag-Sn Alloy Ag-Sn Alloy • Ag3Sn + Cu3Sn + HgÞAg3Sn + Cu3Sn + Ag2Hg3 + Cu6Sn5     1  Phillip’s Science of Dental Materials 2003 Single Composition High-Copper Alloys • Gamma 1 (1) (Ag2Hg3) crystalsgrow binding together partially-dissolved gamma () alloyparticles (Ag3Sn) • Epsilon () (Cu3Sn) develops crystals on surface of gamma particle (Ag3Sn) in the form of eta () (Cu6Sn5) • reduces creep • prevents gamma-2 formation  1

  27. Classifications • Based on copper content • Based on particle shape • Based on method of adding copper

  28. Copper Content • Low-copper alloys • 4 to 6% Cu • High-copper alloys • thought that 6% Cu was maximum amount • due to fear of excessive corrosion and expansion • Now contain 9 to 30% Cu • at expense of Ag Phillip’s Science of Dental Materials 2003

  29. Lathe cut low Cu New TrueDentalloy high Cu ANA 2000 Admixture high Cu Dispersalloy, Valiant PhD Spherical low Cu Cavex SF high Cu Tytin, Valiant Particle Shape

  30. Method of Adding Copper • Single Composition Lathe-Cut (SCL) • Single Composition Spherical (SCS) • Admixture: Lathe-cut + Spherical Eutectic (ALE) • Admixture: Lathe-cut + Single Composition Spherical (ALSCS)

  31. Single Composition Lathe-Cut (SCL) • More Hg needed than spherical alloys • High condensation force needed due to lathe cut • 20% Cu • Example • ANA 2000 (Nordiska Dental)

  32. Single Composition Spherical (SCS) • Spherical particles wet easier with Hg • less Hg needed (42%) • Less condensation force, larger condenser • Gamma particles as 20 micron spheres • with epsilon layer on surface • Examples • Tytin (Kerr) • Valiant (Ivoclar Vivadent)

  33. Admixture: Lathe-cut + Spherical Eutectic (ALE) • Composition • 2/3 conventional lathe cut (3% Cu) • 1/3 high Cu spherical eutectic (28% Cu) • overall 12% Cu, 1% Zn • Initial reaction produces gamma 2 • no gamma 2 within two years • Example • Dispersalloy (Caulk)

  34. Admixture: Lathe-cut + Single Composition Spherical (ALSCS) • High Cu in both lathe-cut and spherical components • 19% Cu • Epsilon layer forms on both components • 0.5% palladium added • reinforce grain boundaries on gamma 1 • Example • Valiant PhD (Ivoclar Vivadent)

  35. Manufacturing Process • Lathe-cut alloys • Ag & Sn melted together • alloy cooled • phases solidify • heat treat • 400 ºC for 8 hours • grind, then mill to 25 - 50 microns • heat treat to release stresses of grinding Phillip’s Science of Dental Materials 2003

  36. Manufacturing Process • Spherical alloys • melt alloy • atomize • spheres form as particles cool • sizes range from 5 - 40 microns • variety improves condensability Phillip’s Science of Dental Materials 2003

  37. Material-Related Variables • Dimensional change • Strength • Corrosion • Creep

  38. Dimensional Change • Most high-copper amalgams undergo a net contraction • Contraction leaves marginal gap • initial leakage • post-operative sensitivity • reduced with corrosion over time Phillip’s Science of Dental Materials 2003

  39. Dimensional Change • Net contraction • type of alloy • spherical alloys have more contraction • less mercury • condensation technique • greater condensation = higher contraction • trituration time • overtrituration causes higher contraction Phillip’s Science of Dental Materials 2003

  40. Strength • Develops slowly • 1 hr: 40 to 60% of maximum • 24 hrs: 90% of maximum • Spherical alloys strengthen faster • require less mercury • Higher compressive vs. tensile strength • Weak in thin sections • unsupported edges fracture Phillip’s Science of Dental Materials 2003

  41. Corrosion • Reduces strength • Seals margins • low copper • 6 months • SnO2, SnCl • gamma-2 phase • high copper • 6 - 24 months • SnO2 , SnCl, CuCl • eta-phase (Cu6Sn5) Sutow J Dent Res 1991

  42. Creep • Slow deformation of amalgam placed under a constant load • load less than that necessary to produce fracture • Gamma 2 dramatically affects creep rate • slow strain rates produces plastic deformation • allows gamma-1 grains to slide • Correlates with marginal breakdown Phillip’s Science of Dental Materials 2003

  43. Creep • High-copper amalgams have creep resistance • prevention of gamma-2 phase • requires >12% Cu total • single composition spherical • eta (Cu6Sn5) embedded in gamma-1 grains • interlock • admixture • eta (Cu6Sn5) around Ag-Cu particles • improves bonding to gamma 1 Click here for table of creep values

  44. Dentist-Controlled Variables • Manipulation • trituration • condensation • burnishing • polishing

  45. Trituration • Mixing time • refer to manufacturerrecommendations • Click here for details • Overtrituration • “hot” mix • sticks to capsule • decreases working / setting time • slight increase in setting contraction • Undertrituration • grainy, crumbly mix Phillip’s Science of Dental Materials 2003

  46. Condensation • Forces • lathe-cut alloys • small condensers • high force • spherical alloys • large condensers • less sensitive to amount of force • vertical / lateral with vibratory motion • admixture alloys • intermediate handling between lathe-cut and spherical

  47. Burnishing • Pre-carve • removes excess mercury • improves margin adaptation • Post-carve • improves smoothness • Combined • less leakage Ben-Amar Dent Mater 1987

  48. Early Finishing • After initial set • prophy cup with pumice • provides initial smoothness to restorations • recommended for spherical amalgams

  49. Polishing • Increased smoothness • Decreased plaque retention • Decreased corrosion • Clinically effective? • no improvement in marginal integrity • Mayhew Oper Dent 1986 • Collins J Dent 1992 • Click here for abstract

  50. Alloy Selection • Handling characteristics • Mechanical and physicalproperties • Clinical performance Click here for more details

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