AMALGAM

AMALGAM

Product of amalgamation
Alloy and mercury react to form silver hard grey mass
2 compositions: conventional + high copper
CONVENTIONAL
1. 65%Ag = Silver
2. 29%Sn = Tin
3. 6%Cu = copper
4. 2%Zn = Zinc
5. 3%Hg = Mercury
Today-traditional conventional superseded by high copper
HIGH COPPER
1. 40%Ag = Silver
2. 32%Sn = Tin
3. 30%Cu = copper
4. 2%Zn = zinc
5. 3% Hg = Mercury
Variations in alloy morphology:
LATHE CUT + SPHERICAL
Cu has strengthening affect
1. Zn acts as a SCAVENGER in alloy production
2. MIxing termed TRITURATION
3. Hg diffuses into alloy = >30mins small shrinkage
4. >30-60mins = expansion due to crystallisation
5. Overall effect is a net EXPANSION/CONTRACTION
6. Weak in thin sections
PLACEMENT TO FUNCTION
1. 15-20mins and 24 hrs final strength
PROPERTIES - CREEP
1. Plastic deformation under load
2. Clinically flows manifestations of protrusions at rest margins
3. # off producing DITCHING
4. GAMMA 2 largely responsible
5. Corrosion of allot exacerbates release of Hg in marginal crevice
PROPERTIES - CORROSION
1. Electromechanical interactions of different alloy phases with SALIVA as ELECTOLYTE
2. GAMMA 2 phase Anode
3. GAMMA 2 breaks down to Sn(tin) + Hg(mercury)
4. Not all bad as corrosion products provide marginal seal
5. In high copper phase undergoing most corrosion is Cu +sn
PROPERTIES - THERMAL
1. High thermal diffusity
2. Thermal expansion of dentine
BIOLOGICAL PROPERTIES
1. Hg compounds known to be toxic to CNS
2. No conclusive evidence but percieved elevated risk:
3. Hg dose HIGH DURING PLACEMENT+CARVING
4. Hg CONCENTRATES+CROSSES PLACENTA
MANIPULATIVE VARIABLES
1. Alloy:Hg ratio
2. Drier mix achieved by mechanical mix
3. packing+condensing removes excess Hg
MANUFACTURER VARIABLES
1. Particle size of alloy: small achieves higher1x24hr strenght
2. If extremely small- too rapid set+cannot remove Hg layer

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