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 • • 1895 powdered silver coins mixed with mercury – expanded on setting – 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 • require less mercury – smaller surface area easier to wet » 40 to 45% Hg Click here for ADA Mercury Hygiene Recommendations – 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  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 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) – 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-Sn Alloy Ag Sn Sn Ag Sn Ag Ag-Sn Alloy Mercury (Hg)

Ag  3 Sn + Hg  Ag 3 Sn + Ag  2  Hg 1 3 + Sn 8  Hg 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 Ag-Sn Alloy Ag Sn Sn Ag Sn Ag Ag-Sn Alloy Mercury Hg

Ag  3 Sn + Hg  Ag 3 Sn + Ag  2  Hg 1 3 + Sn 8  Hg 2 Phillip’s Science of Dental Materials 2003

Conventional Low-Copper Alloys

• Gamma 1 ( 

1

) = Ag 2 Hg 3 – matrix for unreacted alloy and 2nd strongest phase – 10 micron grains binding gamma (  ) – 60% of volume

Ag-Sn Alloy Ag-Sn Alloy



1 Ag-Sn Alloy

Ag  3 Sn + Hg  Ag 3 Sn + Ag  2  Hg 1 3 + Sn 8  Hg 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 volume decreases with time due to corrosion

Ag-Sn Alloy Ag-Sn Alloy



2 Ag-Sn Alloy

Ag  3 Sn + Hg  Ag 3 Sn + Ag  2  Hg 1 3 + Sn 8  Hg 2 Phillip’s Science of Dental Materials 2003

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 Ag 3 Sn particles

Ag-Cu Alloy Hg Ag-Sn Alloy Hg Ag Sn Ag Ag Ag Sn Ag-Sn Alloy Mercury

Ag  3 Sn + Ag-Cu + Hg  Ag  3 Sn + Ag-Cu + Ag 2  Hg 1 3 + Cu 6 Sn  5 Phillip’s Science of Dental Materials 2003

Admixed High-Copper Alloys

• Sn diffuses to surface of Ag-Cu particles – reacts with Cu to form (eta) Cu 6 Sn 5 (  ) • around unconsumed Ag-Cu particles 

Ag-Sn Alloy Ag-Cu Alloy Ag-Sn Alloy

Ag  3 Sn + Ag-Cu + Hg  Ag  3 Sn + Ag-Cu + Ag 2  Hg 1 3 + Cu 6 Sn  5 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-Sn Alloy Ag-Cu Alloy Ag-Sn Alloy



1

Ag  3 Sn + Ag-Cu + Hg  Ag  3 Sn + Ag-Cu + Ag 2  Hg 1 3 + Cu 6 Sn  5 Phillip’s Science of Dental Materials 2003

Single Composition High-Copper Alloys

• Gamma sphere (  ) (Ag 3 Sn) with epsilon coating (  ) (Cu 3 Sn) • Ag and Sn dissolve in Hg 

Ag-Sn Alloy Ag Ag-Sn Alloy Sn Ag Sn Ag-Sn Alloy Mercury (Hg)

Ag  3 Sn + Cu 3  Sn + Hg  Ag 3  Sn + Cu 3  Sn + Ag 2  Hg 1 3 + Cu 6 Sn  5 Phillip’s Science of Dental Materials 2003

Single Composition High-Copper Alloys

• Gamma 1 ( 

1

) (Ag 2 Hg 3 ) crystals grow binding together partially dissolved 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 ) – reduces creep – prevents gamma-2 formation 

Ag-Sn Alloy Ag-Sn Alloy



1 Ag-Sn Alloy

Ag  3 Sn + Cu 3  Sn + Hg  Ag 3  Sn + Cu 3  Sn + Ag 2  Hg 1 3 + Cu 6 Sn  5 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 PhD • 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 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 – – SnO 2 , SnCl gamma-2 phase – high copper • 6 - 24 months – SnO 2 , SnCl, CuCl – 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 – – slight increase in setting contraction • Undertrituration – decreases working / setting time 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 Type

Amalgam Properties

Compressive Strength (MPa) 1 hr 7 days % Creep Tensile Strength (24 hrs) (MPa) Low Copper 1 Admixture 2 145 137 343 431 2.0

0.4

60 48 Single Composition 3 1 Fine Cut, Caulk 2 Dispersalloy, Caulk 3 Tytin, Kerr 262 510 0.13

64 Phillip’s Science of Dental Materials 2003

Survey of Practice Types

Civilian General Dentists

32%

Amalgam Free Amalgam Users

68%

Haj-Ali Gen Dent 2005

Frequency of Posterior Materials

by Practice Type

7% 3% 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 your practice?

22%

No Yes Do you place fewer amalgams than 5 years ago?

12%

No 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 Comp Inlays Longitudinal Ceramic Inlays CAD/CAM Inlays Gold Inlays & Onlays Cross-Sectional GI

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 Am al ga Di m re ct C om p Co m po m Co er m p In Ce la ra ys m ic In la ys CA D/ CA M Ca st G ol d GI Tu nn el ART

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]