Amalgam

Question 1

What is the controversy with amalgam

Answer 1

Concerns over health risk as mercury is one of its constituents
No conclusion on whether it is responsible for various diseases

Question 2

What is amalgam

Answer 2

An alloy formed by the reaction of mercury (liquid) and silver, tin, copper and other metals (powder)

Question 3

What is the composition of amalgam

Answer 3

70% Silver
25% Tin
3% Copper
1% Zinc
1% Mercury

Question 4

How can amalgam be classified

Answer 4

By composition - traditional or copper enriched

By type of powder particles - lathe-cut or spherical

Question 5

What are the functions of the powders in amalgam and how much weight does this take up

Answer 5

50% by weight
Silver and tin - Ag3Sn, known as the y phase, reacts with mercury to form amalgam
Copper - increases strength and hardness
Zinc - preferentially reacts with oxygen
Mercury in powder - accelerates the setting reaction

Question 6

What are the functions of the liquids in amalgam and how much weight do they take up

Answer 6

50% by weight
Hg
Triple distilled (very pure)
Reacts with other metals

Question 7

Describe the setting reaction of amalgam

Answer 7

AgSn powder reacts with Hg liquid
This produces silver-mercury GAMMA-1 phase and tin-mercury GAMMA-2 phase
It leaves unreacted AgSn - the GAMMA phase

Question 8

Describe lathe-cut amalgam particles

Answer 8

Course, medium and fine

Formed by filling solid ingots of amalgam

Question 9

Describe spherical amalgam, particles

Answer 9

Range of particle sizes

Formed by spraying molten amalgam into an inert atmosphere

Question 10

Describe the setting dimensional changes of hand-mixed amalgam

Answer 10

Initially contracts and then expands

Question 11

Describe the setting dimensional changes of mechanically mixed amalga,

Answer 11

Undergoes a small contraction which is achieved quite quickly and then maintained

Question 12

Why are most amalgams zinc free

Answer 12

Zinc can interact with saliva and blood forming bubbles of H2 within the amalgam
This pressure builds up causing expansion
Downwards pressure causes pulpal pain
Upwards pressure causes the restoration to sit above the surface

Question 13

What are the different handling factors of amalgam

Answer 13

Proportioning of powder and liquid
How well they are mixed in the amalgamator
How well it is packed into the cavity
How skilfully carving and polishing are carried out

Question 14

What can affect the performance of amalgam

Answer 14

Handling factors
Cavity design
Corrosion
Variations between brands

Question 15

What are the advantages of using amalgam with spherical particles

Answer 15

Less Hg needed
Higher tensile strength
Higher early compressive strength 
Less sensitive to condensation
Easier to carve into shape