Amalgam

Dental AmalgamDental Amalgam

Col Kraig S. VandewalleUSAF 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-Cueutectic 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


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


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


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

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


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


Basic Setting Reactions

• Conventional low-copper alloys

• Admixed high-copper alloys

• Single composition high-copper alloys

• Dissolution and precipitation • Hg dissolves Ag and Sn

from alloy• Intermetallic compounds

formed Ag-Sn Alloy

Ag-Sn Alloy

Ag-Sn Alloy

Mercury (Hg)

AgAgAg

Sn

Sn

Sn

Conventional Low-Copper Alloys

Hg Hg

AgAg33Sn + HgSn + Hg AgAg33Sn + AgSn + Ag22HgHg33 + Sn + Sn88HgHg


1 2


• Gamma () = Ag3Sn– unreacted alloy– strongest phase and

corrodes the least– forms 30% of volume

of set amalgam

Ag-Sn Alloy

Ag-Sn Alloy

Ag-Sn Alloy

Mercury

Ag

AgAg

Sn

Sn

Sn

HgHg

Hg



1 2


• Gamma 1 (1) = Ag2Hg3

– matrix for unreacted alloyand 2nd strongest phase

– 10 micron grainsbinding gamma ()

– 60% of volume

1



1 2

Ag-Sn Alloy

Ag-Sn Alloy

Ag-Sn Alloy


• 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



1 2

2

Ag-Sn Alloy

Ag-Sn Alloy

Ag-Sn Alloy

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


AgAg33Sn + Ag-Cu + HgSn + Ag-Cu + Hg AgAg33Sn + Ag-Cu + AgSn + Ag-Cu + Ag22HgHg33 + Cu + Cu66SnSn55 1

Ag-Sn Alloy

Ag-Sn Alloy

Mercury

Ag

AgAg

SnSn

Ag-Cu Alloy

AgHgHg


• Sn diffuses to surface of Ag-Cu particles – reacts with Cu to form

(eta) Cu6Sn5 ()• around unconsumed

Ag-Cu particles

Ag-Sn Alloy

Ag-Cu Alloy

Ag-Sn Alloy




• Gamma 1 (1) (Ag2Hg3)

surrounds () eta phase (Cu6Sn5) and gamma ()

alloy particles (Ag3Sn) Ag-Sn Alloy

1

Ag-Cu Alloy

Ag-Sn Alloy



Single Composition High-Copper Alloys

• Gamma sphere () (Ag3Sn) with epsilon coating () (Cu3Sn)

• Ag and Sn dissolve in Hg

Ag-Sn Alloy

Ag-Sn AlloyAg-Sn Alloy

Mercury (Hg)

Ag

SnAg

Sn

AgAg33Sn + CuSn + Cu33Sn + HgSn + Hg AgAg33Sn + CuSn + Cu33Sn + AgSn + Ag22HgHg33 + Cu + Cu66SnSn55


1

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

Ag-Sn Alloy

Ag-Sn AlloyAg-Sn Alloy

1

AgAg33Sn + CuSn + Cu33Sn + HgSn + Hg AgAg33Sn + CuSn + Cu33Sn + AgSn + Ag22HgHg33 + Cu + Cu66SnSn55


1

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


Particle Shape

• 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

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


Manufacturing Process

• Spherical alloys– melt alloy– atomize

• spheres form as particles cool

– sizes range from 5 - 40 microns• variety improves condensability


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


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


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


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


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 manufacturerrecommendations

• Click here for details

• Overtrituration– “hot” mix

• sticks to capsule

– decreases working / setting time– slight increase in setting contraction

• Undertrituration– grainy, crumbly mix


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 physicalproperties

• 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


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 Copper1 145 343 2.0 60

Admixture2 137 431 0.4 48

Single Composition3

262 510 0.13 64


1Fine Cut, Caulk 2 Dispersalloy, Caulk 3Tytin, Kerr

Survey of Practice TypesCivilian General Dentists

68%

32%

Amalgam Users

Amalgam Free

Haj-Ali Gen Dent 2005

Frequency of Posterior Materialsby Practice Type

39%

51%

3% 7%

Amalgam Direct Composite Indirect Composite Other

3%

77%

8%

12%

Amalgam Users

Amalgam Free

Haj-Ali Gen Dent 2005

Profile of Amalgam UsersCivilian Practitioners

78%

22%

Do you use amalgam in your practice?

Yes

No

DPR 2005

88%

12%

Do you place fewer amalgams than 5 years ago?

Yes

No

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

0

2

4

6

8

Amalgam DirectComp

CompInlays

CeramicInlays

CAD/CAMInlays

GoldInlays &Onlays

GI

Longitudinal Cross-Sectional

Hickel J Adhes Dent 2001

% Annual Failure

0

5

10

15

Amalg

am

Direct

Com

p

Compo

mer

Comp

Inlay

s

Ceram

ic In

lays

CAD/CAM

Cast G

old GI

Tunn

elART

% Annual Failure

Manhart Oper Dent 2004 Click here for abstract

Standard Deviation

Longitudinal and Cross-Sectional Data

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

Acknowledgements• Dr. David Charlton

• Dr. Charles Hermesch

• Col Salvador Flores

Questions/CommentsCol Kraig Vandewalle

– DSN 792-7670

– [email protected]

Amalgam

Documents

alloy of mercury

admixed highcopper alloys

precipitation hg dissolves

ag2hg3agsn alloy matrix

basic constituents mercury

modern amalgam alloy

low cu alloys

mercury lathe