Powder component of Amalgam
- Silver + Tin (intermetallic compound form) Ag3Sn
- Copper (increase strength and hardness)
- Zinc (scavenger in production - forms slag) - now not really used***
- Powdered mercury in pre- amalgamated materials
Liquid component of Amalgam
- Liquid mercury- triple distilled so its is very pure
Name the different γ components of amalgam and their properties
γ-Ag3Sn (high strength + corrosion resistance)
γ1- Ag2Hg3 (
γ2- Sn7Hg9
Recite the setting reaction for amalgam
powder + liquid > unreacted particles of γ + amalgam matrix made of γ1 + γ2
Ag3Sn + Hg > Ag3Sn (unreacted) + Ag2Hg3 + Sn7Hg9
Why is Zinc no longer used in Amalgam
- zinc reacts with saliva and incorporates Hydrogen gas
- The gas causes downward pressure which creates plural pain
- it also causes upward pressure and therefore which causes the amalgam to sit proud
Describe the stages of Amalgam creep
1) Amalgam is subjected to small repetitive stress
2) it deforms and sits proud of surface
3) the margins become ditched and leaves exposed tooth margins to secondary caries
What factors affect amalgam strength
- Amalgam strength ok after 24 hours
- undermining
- excessive mercury content
- poor condensation pressure
- slow rate of packing (increments don’t bond together)
- corrosion by oral fluids
Describe the difference when Copper is added to amalgam
γ becomes AgSnCu
γ2 becomes Cu6Sn5
gives a better early strength
less creep
better corrosion resistance
increased marginal durability
