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 – 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

– SnO2, SnCl – gamma-2 phase – high copper • 6 - 24 months

– SnO2 , SnCl, CuCl – eta-phase (Cu6Sn5)

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 (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 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 % Creep Tensile Strength Strength (MPa) (24 hrs) (MPa)

Amalgam Type 1 hr 7 days

Low Copper1 145 343 2.0 60

Admixture2 137 431 0.4 48

Single 262 510 0.13 64 Composition3

1Fine Cut, Caulk 2 Dispersalloy, Caulk 3Tytin, Kerr Phillip’s Science of Dental Materials 2003 Survey of Practice Types Civilian General Dentists

32% Amalgam Amalgam Free Users

68%

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

3% 7%

39% Amalgam Users

51%

Amalgam Direct Composite Indirect Composite Other

12% 3% 8% Amalgam Free

Haj-Ali Gen Dent 2005 77% Profile of Amalgam Users Civilian Practitioners

Do you use amalgam in Do you place fewer amalgams your practice? than 5 years ago?

22% 12% No No Yes Yes

78% 88%

DPR 2005 Review of Clinical Studies (Failure Rates in Posterior Permanent Teeth)

% Annual Failure 8

6

4

2

0 Amalgam Direct Comp Ceramic CAD/CAM Gold GI Comp Inlays Inlays Inlays Inlays & Onlays

Longitudinal Cross-Sectional

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

% Annual Failure

15

Standard Deviation 10 Longitudinal and Cross-Sectional Data 5

0

GI ART Tunnel Amalgam CAD/CAMCast Gold Compomer Direct Comp Comp Inlays Ceramic Inlays 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 – [email protected]