Amalgam

Question 1

What is amalgamation?

Answer 1

Process of combining alloy materials with mercury

Question 2

Composition of amalgam

Answer 2

Silver, tin, copper, zinc, other materials, Mercury

Question 3

What does silver contribute to?

Answer 3

Strength of amalgam, long term brightness, decreases corrosion, decreases creep and setting time.

Too much silver causes excessive expansion during setting. Alloys with 70%+ silver not stronger than 70%-

Question 4

What does tin do? (Food and bad)

Answer 4

Promotes amalgamation with mercury, reduces expansion.

Excess of tin = contraction, decreases strength, increased setting time, corrosion, plasticity.

Question 5

What does copper do?

Answer 5

Improves strength, decreases setting time, decreases corrosion and creep, increases setting expansion, decreases plasticity.

Excess= tarnish, discolouration

Question 6

Properties of zinc

Answer 6

Removes unwanted oxides during manufacturing, “cleaner” amalgam, improves corrosion resistance, shiny, if contaminated with water will expand excessively.

Question 7

Properties, advantages and disadvantages of mercury

Answer 7

Is a matrix material=temporary liquid stage.
Ad- gives plasticity and softness, binds the particle of the alloy together, necessary for the setting reaction and hardening.
Dis- if in excess= low strength, high creep.

Question 8

Lathe cut and spherical cut alloy % and properties

Answer 8

Lathe cut = 50% - irregular shaped, fine, micro cut or course. Require high condensation pressure
Spherical cut = 42% - atomised, round, require less mercury and give more early strength but more micro leakage

Admix- provides best qualities of both

Question 9

Advantages of high copper alloys

Answer 9

Physical properties are improved, better corrosion resistance, less creep, better marginal integrity, easier polishing, superior clinical performance, elimination of gamma 2 phase in set amalgam

Question 10

What is corrosion?

Answer 10

Breakdown of restoration. To minimise, use high copper alloy, use correct trituration, condensation and avoid moisture contamination

Question 11

What is creep

Answer 11

Slow deformation over time. To minimise, use high copper alloy

Question 12

Reasons for excessive expansion/contraction.

Answer 12

Contraction - over trituration

Expansion - under trituration, poor condensation, moisture contamination

Question 13

Amalgam phases

Answer 13

Gamma (Ag+Sn) 
Gamma 1 (ag+hg) happens in mixing
Gamma 2 (an+hg) happens in mixing 
Epsilon (cu+sn) happens/sets in the mouth 
Eta (cu+sn) happens after 24hrs

Question 14

Which is the weakest phase?

Answer 14

Gamma 2. Corrodes easily.

Question 15

Properties of amalgam

Answer 15

Expansion
Contraction
Strength 
Tarnish and corrosion
Creep

Question 16

To maximise strength of amalgam you must:

Answer 16

Use high copper alloy, pre weighted
Triturate for correct time
Appropriate condensation pressure
Maintain dry field
Use small increments

Question 17

After condensation amalgam does….

Answer 17

Slight contraction may be observed

Then a slower expansion (gamma 1 crystals grow)

Question 18

Steps in amalgam placement

Answer 18

Trituration
Condensation
Adaptation
Carving, finishing, polishing

Question 19

Why place a liner at the base of your filling

Answer 19

To protect pulp or to aid in pulp recovery
Protect pulp from heat (thermal conductivity)
Ingredients of most filling materials are not biocompatible with pulp
Protect dentine and pulp from occlusal forces
Inhibits noxious products and bacteria through microleakage
(If filling leaks, base is protected)

Question 20

Advantages and disadvantages of amalgam

Answer 20

Ad- high strength, longevity, wear resistant, easy to use, maintains anatomical form, cheap, clinical proven success,

Dis- invasive, not bonded, expansion/contraction, electro galvanism and corrosion, mercury toxicity, aesthetics.