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) • 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 Overview • History • Basic composition • Basic setting reactions • Classifications • Manufacturing • Variables in amalgam performance Click here for briefing on dental amalgam (PDF) History • 1833 – Crawcour brothers introduce amalgam 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 History • 1960’s – conventional low-copper lathe-cut alloys • smaller particles – first generation high-copper alloys • Dispersalloy (Caulk) – admixture of spherical Ag-Cu eutectic particles with conventional lathe-cut – eliminated gamma-2 phase Mahler J Dent Res 1997 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 Amalgam • An alloy of mercury with another metal. 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) Constituents in Amalgam • Basic – Silver – Tin – Copper – Mercury • Other – Zinc – Indium – Palladium Basic Constituents • Silver (Ag) – increases strength – increases expansion • Tin (Sn) – decreases expansion – decreased strength – increases setting time Phillip’s Science of Dental Materials 2003 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 Basic Constituents • Mercury (Hg) – activates reaction – only pure metal that is liquid at room temperature – spherical alloys Click here for ADA Mercury Hygiene Recommendations • 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 Phillip’s Science of Dental Materials 2003 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 H2O + Zn ZnO + H2 Phillip’s Science of Dental Materials 2003 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 Other Constituents • Palladium (Pd) – reduced corrosion – greater luster – example • Valiant PhD (Ivoclar Vivadent) – 0.5% palladium Mahler J Dent Res 1990 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 – Sn8Hg called gamma 2 • voids Phillip’s Science of Dental Materials 2003 Basic Setting Reactions • Conventional low-copper alloys • Admixed high-copper alloys • Single composition high-copper alloys Conventional Low-Copper Alloys • Dissolution and precipitation • Hg dissolves Ag and Sn Ag-Sn Alloy from alloy Hg Hg Sn Ag Ag Ag • Intermetallic compounds Sn Ag-Sn Sn Ag-Sn Alloy Alloy formed Mercury (Hg) Ag3Sn + Hg Ag3Sn + Ag2Hg3 + Sn8Hg 1 2 Phillip’s Science of Dental Materials 2003 Conventional Low-Copper Alloys • Gamma ( ) = Ag3Sn Hg – unreacted alloy Ag-Sn Alloy – strongest phase and Hg Hg Ag Sn Ag corrodes the least Ag Sn – forms 30% of volume Ag-Sn Sn Ag-Sn Alloy Alloy of set amalgam Mercury Ag3Sn + Hg Ag3Sn + Ag2Hg3 + Sn8Hg 1 2 Phillip’s Science of Dental Materials 2003 Conventional Low-Copper Alloys • Gamma 1 ( 1) = Ag2Hg3 Ag-Sn Alloy – matrix for unreacted alloy and 2nd strongest phase – 10 micron grains 1 Ag-Sn Ag-Sn binding gamma ( ) Alloy Alloy – 60% of volume Ag3Sn + Hg Ag3Sn + Ag2Hg3 + Sn8Hg 1 2 Phillip’s Science of Dental Materials 2003 Conventional Low-Copper Alloys • Gamma 2 ( 2) = Sn8Hg Ag-Sn Alloy – weakest and softest phase – corrodes fast, voids form – corrosion yields Hg which reacts with more gamma ( ) Ag-Sn Ag-Sn Alloy – 10% of volume Alloy 2 – volume decreases with time due to corrosion Ag3Sn + Hg Ag3Sn + Ag2Hg3 + Sn8Hg 1 2 Phillip’s Science of Dental Materials 2003 Admixed High-Copper Alloys • Ag enters Hg from Ag-Cu spherical eutectic particles Ag-Cu Alloy – eutectic • Hg an alloy in which the elements Hg Ag Ag are completely soluble in liquid Ag Ag solution but separate into distinct Sn areas upon solidification Ag-Sn Sn Ag-Sn Alloy Alloy • Both Ag and Sn enter Hg Mercury from Ag3Sn particles Ag3Sn + Ag-Cu + Hg Ag3Sn + Ag-Cu + Ag2Hg3 + Cu6Sn5 1 Phillip’s Science of Dental Materials 2003 Admixed High-Copper Alloys • Sn diffuses to surface of Ag-Cu particles Ag-Cu Alloy – reacts with Cu to form (eta) Cu6Sn5 ( ) Ag-Sn • Ag-Sn around unconsumed Alloy Alloy Ag-Cu particles Ag3Sn + Ag-Cu + Hg Ag3Sn + Ag-Cu + Ag2Hg3 + Cu6Sn5 1 Phillip’s Science of Dental Materials 2003 Admixed High-Copper Alloys • Gamma 1 ( ) (Ag Hg ) 1 2 3 Ag-Cu Alloy surrounds ( ) eta phase (Cu6Sn5) and gamma ( ) alloy particles (Ag Sn) 3 Ag-Sn Ag-Sn Alloy Alloy 1 Ag3Sn + Ag-Cu + Hg Ag3Sn + Ag-Cu + Ag2Hg3 + Cu6Sn5 1 Phillip’s Science of Dental Materials 2003 Single Composition High-Copper Alloys • Gamma sphere ( ) (Ag3Sn) with epsilon coating ( ) Ag-Sn Alloy Ag (Cu3Sn) Sn Sn Ag • Ag and Sn dissolve in Hg Ag-Sn Alloy Ag-Sn Alloy Mercury (Hg) Ag3Sn + Cu3Sn + Hg Ag3Sn + Cu3Sn + Ag2Hg3 + Cu6Sn5 1 Phillip’s Science of Dental Materials 2003 Single Composition High-Copper Alloys • Gamma 1 ( 1) (Ag2Hg3) crystals grow binding together partially- Ag-Sn Alloy dissolved gamma ( ) alloy particles (Ag3Sn) • Epsilon (Cu Sn) develops ( ) 3 Ag-Sn Alloy crystals on surface of Ag-Sn Alloy gamma particle (Ag3Sn) 1 in the form of eta ( ) (Cu6Sn5) – reduces creep – prevents gamma-2 formation Ag3Sn + Cu3Sn + Hg Ag3Sn + Cu3Sn + Ag2Hg3 + Cu6Sn5 1 Phillip’s Science of Dental Materials 2003 Classifications • Based on copper content • Based on particle shape • Based on method of adding copper 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 Particle Shape • Lathe cut • Spherical – low Cu – low Cu • New True • Cavex SF Dentalloy – high Cu – high Cu • Tytin, Valiant • ANA 2000 • Admixture – high Cu • Dispersalloy, Valiant PhD 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) 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) 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) 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) 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) 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 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 Material-Related Variables • Dimensional change • Strength • Corrosion • Creep 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 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 Strength • Develops slowly – 1 hr: 40 to 60% of maximum