AMALGAM

AMALGAM

1. Product of amalgamation

2. Alloy and mercury react to form silver hard grey mass

3. 2 compositions: conventional + high copper

4. CONVENTIONAL

   • 65%Ag = Silver
   • 29%Sn = Tin
   • 6%Cu = copper
   • 2%Zn = Zinc
   • 3%Hg = Mercury

5. Today-traditional conventional superseded by high copper

6. HIGH COPPER

   • 40%Ag = Silver
   • 32%Sn = Tin
   • 30%Cu = copper
   • 2%Zn = zinc
   • 3% Hg = Mercury

7. Variations in alloy morphology:

8. LATHE CUT + SPHERICAL

9. Cu has strengthening affect

   • Zn acts as a SCAVENGER in alloy production
   • MIxing termed TRITURATION
   • Hg diffuses into alloy = >30mins small shrinkage
   • >30-60mins = expansion due to crystallisation
   • Overall effect is a net EXPANSION/CONTRACTION
   • Weak in thin sections

10. PLACEMENT TO FUNCTION

    • 15-20mins and 24 hrs final strength

11. PROPERTIES - CREEP

    • Plastic deformation under load
    • Clinically flows manifestations of protrusions at rest margins
    • # off producing DITCHING
    • GAMMA 2 largely responsible
    • Corrosion of allot exacerbates release of Hg in marginal crevice

12. PROPERTIES - CORROSION

    • Electromechanical interactions of different alloy phases with SALIVA as ELECTOLYTE
    • GAMMA 2 phase Anode
    • GAMMA 2 breaks down to Sn(tin) + Hg(mercury)
    • Not all bad as corrosion products provide marginal seal
    • In high copper phase undergoing most corrosion is Cu +sn

13. PROPERTIES - THERMAL

    • High thermal diffusity
    • Thermal expansion of dentine

14. BIOLOGICAL PROPERTIES

    • Hg compounds known to be toxic to CNS
    • No conclusive evidence but percieved elevated risk:
    • Hg dose HIGH DURING PLACEMENT+CARVING
    • Hg CONCENTRATES+CROSSES PLACENTA

15. MANIPULATIVE VARIABLES

    • Alloy:Hg ratio
    • Drier mix achieved by mechanical mix
    • packing+condensing removes excess Hg

16. MANUFACTURER VARIABLES

    • Particle size of alloy: small achieves higher1x24hr strenght
    • If extremely small- too rapid set+cannot remove Hg layer