Dental Amalgam

By: Naghman Zuberi

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

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Phillips 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

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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
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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

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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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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
Ag-Sn
Alloy
Alloy
Mercury
(Hg)
Sn

Ag3Sn + Hg Ag3Sn + Ag2Hg3 + Sn8Hg

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Conventional Low-Copper Alloys

Gamma () = Ag3Sn

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
Ag-Sn
Alloy

Mercury

Ag3Sn + Hg Ag3Sn + Ag2Hg3 + Sn8Hg

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Phillips Science of Dental Materials 2003

Conventional Low-Copper Alloys

Gamma 1 (1) = Ag2Hg3

matrix for unreacted alloy

and 2nd strongest phase
10 micron grains
binding gamma ()
60% of volume

Ag-Sn Alloy

1
Ag-Sn
Alloy

Ag-Sn
Alloy

Ag3Sn + Hg Ag3Sn + Ag2Hg3 + Sn8Hg

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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

Ag-Sn Alloy

Ag-Sn
Alloy

Ag-Sn
Alloy

Ag3Sn + Hg Ag3Sn + Ag2Hg3 + Sn8Hg

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Phillips 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 Ag3Sn particles

Hg

Ag Ag
Ag

Ag-Sn
Alloy

Sn

Hg
Ag

Sn
Ag-Sn
Alloy

Mercury

Ag3Sn + Ag-Cu + Hg Ag3Sn + Ag-Cu + Ag2Hg3 + Cu6Sn5

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Phillips 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 ()

around unconsumed
Ag-Cu particles

Ag-Sn
Alloy

Ag-Sn
Alloy

Ag3Sn + Ag-Cu + Hg Ag3Sn + Ag-Cu + Ag2Hg3 + Cu6Sn5

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Phillips Science of Dental Materials 2003

Admixed High-Copper Alloys

Gamma 1 (1) (Ag2Hg3)
surrounds () eta phase
(Cu6Sn5) and gamma ()
alloy particles (Ag3Sn)

Ag-Cu Alloy

Ag-Sn
Alloy

Ag-Sn
Alloy

Ag3Sn + Ag-Cu + Hg Ag3Sn + Ag-Cu + Ag2Hg3 + Cu6Sn5

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Single Composition
High-Copper Alloys
Gamma sphere () (Ag3Sn)
Ag-Sn Alloy

with epsilon coating ()

Ag
(Cu3Sn)
Sn
Sn
Ag
Ag-Sn Alloy
Ag and Sn dissolve in Hg
Ag-Sn Alloy
Mercury (Hg)

Ag3Sn + Cu3Sn + Hg Ag3Sn + Cu3Sn + Ag2Hg3 + Cu6Sn5

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Phillips Science of Dental Materials 2003

Single Composition
High-Copper Alloys
Gamma 1 (1) (Ag2Hg3) crystals
grow binding together partiallydissolved gamma () alloy
particles (Ag3Sn)

Epsilon () (Cu3Sn) develops

crystals on surface of
gamma particle (Ag3Sn)
in the form of eta () (Cu6Sn5)

Ag-Sn Alloy

Ag-Sn Alloy
Ag-Sn Alloy

reduces creep
prevents gamma-2 formation

Ag3Sn + Cu3Sn + Hg Ag3Sn + Cu3Sn + Ag2Hg3 + Cu6Sn5

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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

Spherical

low Cu
high Cu

Admixture

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

heat treat

phases solidify
400 C for 8 hours

grind, then mill to 25 - 50 microns

heat treat to release stresses of grinding

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Phillips 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

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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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Phillips 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

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Phillips 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
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Phillips 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)

Naghman Zuberi

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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Phillips 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

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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 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

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Phillips 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
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Burnishing
Pre-carve
removes excess mercury
improves margin adaptation

Post-carve

improves smoothness

Combined

less leakage

Naghman Zuberi

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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Phillips Science of Dental Materials 2003

Handling Characteristics
Admixed
advantages
easy to achieve tight contacts
good polish

disadvantages
hardens slowly
lower early strength

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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
Naghman
ZuberiCaulk
3Tytin, Kerr
2 Dispersalloy,

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Phillips Science of Dental Materials 2003

Thanks A Lot
Naghman Zuberi

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