Amalgam

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  • Topic: Silver, Zinc, Copper
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  • Published : December 16, 2012
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Dental amalgam
Sandra Bērziņa

Definitions
Amalgam: alloy of mercury with one or
more other metals
Amalgam alloy: alloy which combines with
mercury to form amalgam
Dental amalgam alloy: alloy that is
combined with mercury to form amalgam
used for dental purposes

Dental amalgam
• Dental amalgam has been the most widely
used material for the restoration of
posterior teeth due to:
– High strength and durability
– Ease of use
– Good physical characteristics

• However, its use has decreased over the
past decade due to concerns regarding:
– Esthetics
– Mercury content

History
• Amalgam was first used by the Chinese.
There is a mention of Silver – Mercury
paste by Su Kung (A.D. 659) in the
Chinese materia medica
• 1826
– introduction of Silver – Mercury paste (pated`argent) by Peter O. Taveau of Paris, France

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

Classification
According to content
– Silver amalgam: Silver more than 65%
– Copper amalgam: 70% Hg and 30% Cu
According to presence or absence of Zn
Zinc containing alloys – more than 0.01% Zn
Zinc free alloys – less than 0.01% Zn

Classification
• According to Copper content
– Low copper alloys (2-4-6% Cu)
– High copper alloys (9-30% Cu)
According to the shape of alloy particles
- Lathe cut
- Spherical
- Admixture

Classification

Spherical

Cu

Cu

Admixed

Lathe cut

Cu

Cu

Classification
• According to number of metals in alloy
– Binary alloy (Ag; Sn)
– Ternary alloy (Ag; Sn; Cu)
– Quaternary alloy (Ag; Sn; Cu; In)

Manufacturing Process
• Lathe-cut alloys



Ag & Sn melted together
alloy cooled




heat treat





phases solidify

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

Amalgam content
• Basic
– Silver
– Tin
– Copper
– Mercury

• Other
– Zinc
– Indium
– Palladium

Basic Constituents
• Silver (Ag)







increases strength
increases expansion
increases corrosion resistance
whitens alloy
decreases creep
decreases setting time

• Tin (Sn)





decreases expansion
decreases strength
decreases corrosion resistance
increases setting time

Basic Constituents
• Copper (Cu)
– ties up tin
• reducing gamma-2 formation








increases strength
increases expansion
increases corrosion resistance
reduces tarnish and corrosion
reduces setting time
reduces creep
• reduces marginal deterioration

Basic Constituents
• Mercury (Hg)
– activates reaction
– only pure metal that is liquid
at room temperature

Other Constituents
• Zinc (Zn)
– used in manufacturing


decreases oxidation of other elements

– provides better clinical performance


less marginal breakdown

– causes delayed expansion with low Cu alloys


if contaminated with moisture during condensation
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

Other Constituents
• Palladium (Pd)
– reduced corrosion
– greater luster

Composition (% by weight)
Metal...
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