Dental Amalgam: Material Properties and its Use in Clinical Dentistry

Question 1

What is an amalgam?

Answer 1

Amalgam is any alloy of mercury with another metal or other metals.

Question 2

What are the types of amalgam that are used in dentistry?

Answer 2

Copper amalgam no longer used

Conventional amalgam

High copper amalgam

Question 3

What is the composition of the alloy powder in dispersalloy amalgam that we use?

Answer 3

Silver (69%), tin (18%), zopper (12%) and zinc (1%)

Question 4

What is the amalgam forming reaction called?

Answer 4

Amalgamation

Question 5

Why is the mixing time 8 seconds?

Answer 5

The composition with the amalgamator we use needs 8 seconds for complete mixture. If a different composition or type of amalgam was used it would require different amount of time.

Question 6

What are the dentist-controlled viariables of application of amalgam?

Answer 6

Trituation (mixing)

Condensation (extra pressure is required to adapt to cavity wall and margin and to get rid of excess mercury)

Burnishing (Carving and burnishing)

Polishing

Question 7

What happens to amalgam if it is undertriturated?

Answer 7

It becomes grainy and crumbly

Question 8

What happens it amalgam is overtriturated?

Answer 8

It sets too quickly

Question 9

What are the types of alloy shaped?

Answer 9

Lathe cut alloys and spherical alloys exist. Lathe cut require small condensers and high force

Spherical alloys

Question 10

What is the purpose of burnishing?

Answer 10

Burnishing removes excess mercury with pressure and improves margin adaptation

Post carving improves smoothness

Combined there is less leakage?

Question 11

What is the most common cause of amalgam failure?

Answer 11

Most important reason for failure of amalgam is premature loading. 1 hour must be given before patient eats.

Question 12

What is the purpose of polishing amalgams?

Answer 12

Increases smoothness

Decreased plaque retention

Decreased corrosion

Clinically effective

Question 13

What happens during amalgamation?

Answer 13

Dissolves the surface of alloy particles to form a plastic mass. Setting and hardening occur as the liquid mercury is consumed in the formation of new solid phases.

Question 14

What are the uses of amalgam?

Answer 14

Direct, permanent posterior restorations

Large foundation restorations

Cares for croensd or fixed partial denture restorations

Question 15

What are the weaknesses of amalgam?

Answer 15

Amalgam is brittle material (wweak under tension strong under compression)

Prone to corrosion

Creep

Question 16

Why is tin used in amalgam?

Answer 16

Because tin gives it a soft consistency at room temperature. (high reactivity and low melting temperature)

Question 17

What is the purpose of high copper in amalgams?

Answer 17

It removes gamma2 phase

Question 18

What are the ADA specs for dimensional changes that take place in dental amalgam?

Answer 18

Amalgam neither contract nor expand more than 20 microns/cm between 5 minutes and 24 hours beginning of trituration

Question 19

What causes contraction of amalgam?

Answer 19

Contraction results as the particles dissolve and the gamma1 grows.

If there is sufficient liquid mercury present to provide a plastic matrix expansion will occur when gamma1 crystals impinge against one another.

Question 20

What does low Hg:alloy ratio lead to?

Answer 20

Lower mercury:alloy ratios and higher condensation pressures leads to less mercury in the mix and thus results in contraction.

Longer trituration times used of smaller particle size alloys leads to accelerated setting and this leads to contraction

Modern amalgams contract automatically due to low Hg:Alloy ratios

Question 21

What is the most easily corroded amalgam phase?

Answer 21

The gamma2 phase

Question 22

What is the most favourable strength characteristics of amalgam?

Answer 22

Resistance to compression forces is the most favourable strength characteristic of amalgam

Question 23

What is creep?

Answer 23

Time dependent plastic deformation