Amalgam

Question 1

Powder component of Amalgam

Answer 1

• 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

Question 2

Liquid component of Amalgam

Answer 2

• Liquid mercury- triple distilled so its is very pure

Question 3

Name the different γ components of amalgam and their properties

Answer 3

γ-Ag3Sn (high strength + corrosion resistance)
γ1- Ag2Hg3 (
γ2- Sn7Hg9

Question 4

Recite the setting reaction for amalgam

Answer 4

powder + liquid > unreacted particles of γ + amalgam matrix made of γ1 + γ2

Ag3Sn + Hg > Ag3Sn (unreacted) + Ag2Hg3 + Sn7Hg9

Question 5

Why is Zinc no longer used in Amalgam

Answer 5

• 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

Question 6

Describe the stages of Amalgam creep

Answer 6

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

Question 7

What factors affect amalgam strength

Answer 7

• 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

Question 8

Describe the difference when Copper is added to amalgam

Answer 8

γ becomes AgSnCu
γ2 becomes Cu6Sn5

gives a better early strength
less creep
better corrosion resistance
increased marginal durability