Amalgam

By: Naghman Zuberi

Dental AmalgamDental Amalgam

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Overview• Basic composition• Basic setting reactions• Classifications• Manufacturing• Variables in amalgam

performance

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Amalgam

• An alloy of mercury with another metal.

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Why Amalgam?

• Inexpensive• Ease of use• Proven track record

– >100 years• Familiarity• Resin-free

– less allergies than composite

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Constituents in Amalgam• Basic

– Silver– Tin– Copper– Mercury

• Other– Zinc– Indium– Palladium

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Basic Constituents

• Silver (Ag)– increases strength– increases expansion

• Tin (Sn)– decreases expansion– decreased strength– increases setting time

Phillip’s Science of Dental Materials 2003

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Basic Constituents• Copper (Cu)

– ties up tin• reducing gamma-2 formation

– increases strength– reduces tarnish and corrosion– reduces creep

• reduces marginal deterioration


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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


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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

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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

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Other Constituents• Palladium (Pd)

– reduced corrosion– greater luster– example

• Valiant PhD (Ivoclar Vivadent)– 0.5% palladium

Mahler J Dent Res 1990

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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


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Basic Setting Reactions

• Conventional low-copper alloys• Admixed high-copper alloys• Single composition high-copper alloys

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• Dissolution and precipitation• Hg dissolves Ag and Sn

from alloy• Intermetallic compounds

formed Ag-SnAlloy

Ag-SnAlloy

Ag-Sn Alloy

Mercury(Hg)

AgAgAg

Sn

SnSn

Conventional Low-Copper Alloys

Hg Hg

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


1 2

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

corrodes the least– forms 30% of volume

of set amalgamAg-SnAlloy

Ag-SnAlloy

Ag-Sn Alloy

Mercury

AgAgAg

Sn

SnSn

HgHg

Hg



1 2

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• Gamma 1 (1) = Ag2Hg3– matrix for unreacted alloy

and 2nd strongest phase– 10 micron grains

binding gamma ()

– 60% of volume

1



1 2

Ag-Sn Alloy

Ag-SnAlloy

Ag-SnAlloy

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Conventional Low-Copper Alloys• 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-SnAlloy

Ag-SnAlloy

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Admixed High-Copper Alloys

• Ag enters Hg from Ag-Cuspherical eutectic particles– eutectic

• an alloy in which the elementsare completely soluble in liquidsolution but separate into distinctareas upon solidification

• Both Ag and Sn enter Hgfrom Ag3Sn particles


AgAg33Sn + AgSn + Ag--Cu + HgCu + Hg AgAg33Sn + AgSn + Ag--Cu + AgCu + Ag22HgHg33 + Cu+ Cu66SnSn55 1

Ag-SnAlloy

Ag-SnAlloy

Mercury

AgAgAg

SnSn

Ag-Cu Alloy

AgHgHg

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

(eta) Cu6Sn5 ()• around unconsumed

Ag-Cu particles

Ag-SnAlloy

Ag-Cu Alloy

Ag-SnAlloy



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• Gamma 1 (1) (Ag2Hg3)surrounds () eta phase(Cu6Sn5) and gamma ()alloy particles (Ag3Sn) Ag-Sn

Alloy

1

Ag-Cu Alloy

Ag-SnAlloy



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Single CompositionHigh-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

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Single CompositionHigh-Copper Alloys

• Gamma 1 (1) (Ag2Hg3) crystalsgrow binding together partially-dissolved gamma () alloyparticles (Ag3Sn)

• Epsilon () (Cu3Sn) developscrystals on surface ofgamma 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

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Classifications• Based on copper content• Based on particle shape• Based on method of adding

copper

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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


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Particle Shape• Lathe cut

– low Cu– high Cu

• Admixture– high Cu

• Spherical– low Cu– high Cu

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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)

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Single Composition Lathe-Cut(SCL)

• More Hg needed than spherical alloys• High condensation force needed due to

lathe cut• 20% Cu

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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

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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

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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

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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


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Manufacturing Process

• Spherical alloys– melt alloy– atomize

• spheres form as particles cool– sizes range from 5 - 40 microns

• variety improves condensability


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Material-Related Variables

• Dimensional change• Strength• Corrosion• Creep

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Dimensional Change• Most high-copper amalgams undergo a

net contraction• Contraction leaves marginal gap

– initial leakage• post-operative sensitivity

– reduced with corrosion over time


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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


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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


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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

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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


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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

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Dentist-Controlled Variables

• Manipulation– trituration– condensation– burnishing– polishing

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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


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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

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Burnishing

• Pre-carve– removes excess mercury– improves margin adaptation

• Post-carve– improves smoothness

• Combined– less leakage

Ben-Amar Dent Mater 1987

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Early Finishing

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

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Polishing

• Increased smoothness• Decreased plaque retention• Decreased corrosion• Clinically effective?

– no improvement in marginal integrity• Mayhew Oper Dent 1986• Collins J Dent 1992

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Alloy Selection

• Handling characteristics• Mechanical and physical

properties• Clinical performance

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Handling Characteristics• Spherical

– advantages• easier to condense

– around pins• hardens rapidly• smoother polish

– disadvantages• difficult to achieve tight contacts• higher tendency for overhangs


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Handling Characteristics• Admixed

– advantages• easy to achieve tight contacts• good polish

– disadvantages• hardens slowly

– lower early strength

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Amalgam PropertiesCompressive

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

SingleComposition3

262 510 0.13 64


1Fine Cut, Caulk2 Dispersalloy, Caulk3Tytin, Kerr

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Thanks A Lot

Amalgam

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