Amalgam Characteristics

Question 1

Describe the strength of amalgam

Answer 1

Able to withstand stresses caused by biting - high compressive and tensile strength
Traditional amalgam has poor strength 1 hour after setting
After 24 hours it is adequate

Question 2

Describe the abrasion resistance of amalgam

Answer 2

High, so suitable for posterior resistance, ensuring the surface remains smooth
Too high for deciduous teeth

Question 3

Describe the creep of amalgam

Answer 3

Results in deformation, hence amalgam is visco-elastic
High in traditional amalgam rather than copper-enriched
Adversely affects the marginal integrity of the restorations which can lead to microleakage

Question 4

What factors decrease the strength of amalgam

Answer 4

Undermixing
Insufficient pressure applied when packing it into a cavity (low condensation pressure)
Slow rate of packing - increments do not bond
Corrosion - it becomes much weaker

Question 5

Describe the biocompatibility of amalgam

Answer 5

Concern about mercury toxicity

Still a consensus that there is no proven harm to humans in using this material - it is biocompatible

Question 6

What is creep

Answer 6

Creep is observed when a material, subjected to low level stresses, applied repeatedly over a long period of time, experiences flow which leads to its’ permanent deformation

Question 7

How does creep affect amalgam

Answer 7

Low level stresses cause the amalgam to protrude where it site above the normal level
Protruding material is vulnerable to subsequent applied stresses making it likely to fracture
This makes microleakage likely

Question 8

Describe amalgams bond to teeth

Answer 8

Doesn’t bond to dentine or enamel
Instead it is mechanically retained in cavities with undercuts
This means removing more hard tissue than for a composite resin

Question 9

Describe the thermal expansion of amalgam

Answer 9

3x greater than that of tooth tissue - not ideal as it makes the development of marginal gaps more likely

Question 10

Describe the thermal conductivity of amalgam

Answer 10

Ability to transmit heat is high, ideally it should be low so that amalgam acts as an insulating layer

Question 11

Describe the thermal diffusivity of amalgam

Answer 11

Value is high - ideally would be low
This means when a transient thermal stimuli is applied - drinking tea - amalgams temperature will change rapidly, posing a thermal risk to the pulp

Question 12

Which phase in amalgam is the most likely to initiate corrosion and why is this

Answer 12

Y2 as it is the most electronegative

Question 13

Is amalgam good aesthetically

Answer 13

No due to silver/grey colour

Question 14

Is amalgam radiopaque

Answer 14

Yes - easily detected by an x-ray

Question 15

Is amalgam anticariogenic

Answer 15

No

Question 16

Does amalgam have a smooth surface

Answer 16

Yes, if polished well

Question 17

Describe the setting shrinkage in amalgam

Answer 17

There is some shrinkage during the setting reaction but it is small