19 AUG 2020 · AMALGAM COMPOSITION
Silver, tin, copper, mercury, zinc, palladium, indium
MERCURY
- Spherical cut – 40-45% – requires less mercury, small surfaces are easier to wet
- Lathe cut – 45%-50% - requires more mercury, more difficult to wet
SILVER ― 40-70% or 65% content
- Increases strength
- Increases expansion
TIN – 25-27%
- Opp to silver
- decreases strength
- decreses expansion
- increases setting time
GAMMA PHASES
Alloy containing mercury
Ag-Sn + Hg ⟶ AgHg + SnHg
Silver Tin + Mercury ⟶ Silver Mercury + Tin Mercury
४ γ1 γ2
(STRONGEST PHASE) (ABUNDANT PHASE) (WEAKEST PHASE)
γ2 - gamma 2 phase - SnHg - Tin Mercury
➢ Disadvantage - Brittle and Corrodes
➢ Advantage - Self Sealing
COPPER – 6%, 13%
Ag-Sn + Cu + Hg ⟶ AgHg + CuSn
४ γ1 eta η
To get eta phase - need 13% Copper ie. high copper amalgam
Q. The copper ratio that eliminates gamma phase 2 = 13 %.
ZINC – 1%
o In Factory, Silver and Tin, they may form oxide
o ∴ they add Zinc (used as oxide scavenger)
o Provides better clinical performance, less marginal breakdown.
o But, In restoration, zinc if contaminated by moisture, it will cause delayed expansionー seen 3-4 days post restoration ー due to release of hydrogen gas.
o Moisture contamination of Zn can be caused during
aー during trituration.
b ー during restoration.