Dental Amalgam Col Kraig S Vandewalle USAF Dental

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 H 2 O + Zn Þ Zn. O + H 2 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 Ph. D (Ivoclar Vivadent) – 0. 5% palladium Mahler J Dent Res 1990

Basic Composition • A silver-mercury matrix containing filler particles of silver-tin • Filler (bricks) – Ag 3 Sn called gamma • can be in various shapes – irregular (lathe-cut), spherical, or a combination • Matrix – Ag 2 Hg 3 called gamma 1 • – cement Sn 8 Hg 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 from alloy • Intermetallic compounds formed Ag-Sn Alloy Hg Hg Ag Ag Ag Sn Sn Ag-Sn Alloy Mercury (Hg) Sn Ag 3 Sn + Hg Þ Ag 3 Sn + Ag 2 Hg 3 + Sn 8 Hg 1 2 Phillip’s Science of Dental Materials 2003

Conventional Low-Copper Alloys • Gamma ( ) = Ag 3 Sn – – – unreacted alloy strongest phase and corrodes the least forms 30% of volume of set amalgam Hg Ag-Sn Alloy Hg Hg Ag Ag-Sn Alloy Sn Sn Ag Ag Sn Mercury Ag-Sn Alloy Ag 3 Sn + Hg Þ Ag 3 Sn + Ag 2 Hg 3 + Sn 8 Hg 1 2 Phillip’s Science of Dental Materials 2003

Conventional Low-Copper Alloys • Gamma 1 ( 1) = Ag 2 Hg 3 – – – matrix for unreacted alloy and 2 nd strongest phase 10 micron grains binding gamma ( ) 60% of volume Ag-Sn Alloy 1 Ag-Sn Alloy Ag 3 Sn + Hg Þ Ag 3 Sn + Ag 2 Hg 3 + Sn 8 Hg 1 2 Phillip’s Science of Dental Materials 2003

Conventional Low-Copper Alloys • Gamma 2 ( 2) = Sn 8 Hg – – – weakest and softest phase corrodes fast, voids form corrosion yields Hg which reacts with more gamma ( ) 10% of volume decreases with time due to corrosion Ag-Sn Alloy 2 Ag-Sn Alloy Ag 3 Sn + Hg Þ Ag 3 Sn + Ag 2 Hg 3 + Sn 8 Hg 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 • 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 Ag 3 Sn particles Hg Ag Ag-Sn Alloy Sn Hg Ag Sn Mercury Ag-Sn Alloy Ag 3 Sn + Ag-Cu + Hg Þ Ag 3 Sn + Ag-Cu + Ag 2 Hg 3 + Cu 6 Sn 5 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) Cu 6 Sn 5 ( ) • around unconsumed Ag-Cu particles Ag-Sn Alloy Ag 3 Sn + Ag-Cu + Hg Þ Ag 3 Sn + Ag-Cu + Ag 2 Hg 3 + Cu 6 Sn 5 1 Phillip’s Science of Dental Materials 2003

Admixed High-Copper Alloys • Gamma 1 ( 1) (Ag 2 Hg 3) surrounds ( ) eta phase (Cu 6 Sn 5) and gamma ( ) alloy particles (Ag 3 Sn) Ag-Cu Alloy Ag-Sn Alloy 1 Ag-Sn Alloy Ag 3 Sn + Ag-Cu + Hg Þ Ag 3 Sn + Ag-Cu + Ag 2 Hg 3 + Cu 6 Sn 5 1 Phillip’s Science of Dental Materials 2003

Single Composition High-Copper Alloys • Gamma sphere ( ) (Ag 3 Sn) Ag-Sn Alloy with epsilon coating ( ) Ag (Cu 3 Sn) Sn Sn Ag Ag-Sn Alloy • Ag and Sn dissolve in Hg Ag-Sn Alloy Mercury (Hg) Ag 3 Sn + Cu 3 Sn + Hg Þ Ag 3 Sn + Cu 3 Sn + Ag 2 Hg 3 + Cu 6 Sn 5 1 Phillip’s Science of Dental Materials 2003

Single Composition High-Copper Alloys • Gamma 1 ( 1) (Ag 2 Hg 3) crystals grow binding together partiallydissolved gamma ( ) alloy particles (Ag 3 Sn) • Epsilon ( ) (Cu 3 Sn) develops crystals on surface of gamma particle (Ag 3 Sn) in the form of eta ( ) (Cu 6 Sn 5) – – Ag-Sn Alloy 1 reduces creep prevents gamma-2 formation Ag 3 Sn + Cu 3 Sn + Hg Þ Ag 3 Sn + Cu 3 Sn + Ag 2 Hg 3 + Cu 6 Sn 5 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 – low Cu • – New True Dentalloy high Cu • ANA 2000 • Admixture – high Cu • Dispersalloy, Valiant Ph. D • Spherical – low Cu • – Cavex SF high Cu • Tytin, Valiant

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 Ph. D (Ivoclar Vivadent)

Manufacturing Process • Lathe-cut alloys – – Ag & Sn melted together alloy cooled • – heat treat • – – phases solidify 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 – 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

Corrosion • Reduces strength • Seals margins – low copper • 6 months – – – Sn. O 2, Sn. Cl gamma-2 phase high copper • 6 - 24 months – Sn. O 2 , Sn. Cl, Cu. Cl – eta-phase (Cu 6 Sn 5) Sutow J Dent Res 1991

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

Creep • High-copper amalgams have creep resistance – prevention of gamma-2 phase • requires >12% Cu total – single composition spherical • eta (Cu 6 Sn 5) embedded in gamma-1 grains – interlock – admixture • eta (Cu 6 Sn 5) around Ag-Cu particles – improves bonding to gamma 1 Click here for table of creep values

Dentist-Controlled Variables • Manipulation – – trituration condensation burnishing polishing

Trituration • Mixing time – refer to manufacturer recommendations • 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

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

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

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

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

Alloy Selection • Handling characteristics • Mechanical and physical properties • Clinical performance Click here for more details

Handling Characteristics • Spherical – advantages • easier to condense – around pins • hardens rapidly • smoother polish – disadvantages • difficult to achieve tight contacts • higher tendency for overhangs Phillip’s Science of Dental Materials 2003

Handling Characteristics • Admixed – advantages • easy to achieve tight contacts • good polish – disadvantages • hardens slowly – lower early strength

Amalgam Properties Compressive Strength (MPa) % Creep Tensile Strength (24 hrs) (MPa) Amalgam Type 1 hr 7 days Low Copper 1 145 343 2. 0 60 Admixture 2 137 431 0. 4 48 Single Composition 3 262 510 0. 13 64 1 Fine Cut, Caulk 3 Tytin, Kerr 2 Dispersalloy, Phillip’s Science of Dental Materials 2003

Survey of Practice Types Civilian General Dentists Amalgam Free Amalgam Users Haj-Ali Gen Dent 2005

Frequency of Posterior Materials by Practice Type Amalgam Users Amalgam Free Haj-Ali Gen Dent 2005

Profile of Amalgam Users Civilian Practitioners Do you use amalgam in your practice? No Do you place fewer amalgams than 5 years ago? No Yes DPR 2005

Review of Clinical Studies (Failure Rates in Posterior Permanent Teeth) % Annual Failure Hickel J Adhes Dent 2001

Review of Clinical Studies (Failure Rates in Posterior Permanent Teeth) % Annual Failure Standard Deviation Longitudinal and Cross-Sectional Data Manhart Oper Dent 2004 Click here for abstract

Acknowledgements • Dr. David Charlton • Dr. Charles Hermesch • Col Salvador Flores Questions/Comments Col Kraig Vandewalle – DSN 792 -7670 – ksvandewalle@nidbr. med. navy. mil