4. Dental Amalgam

Which one of the following is not a classification of amalgam?

• Copper content

• Zinc content

• Particle size

• Filler content

What crystals are associated with Gamma 1 Phase setting reaction?

• Sn7-8Hg

• Ag2Hg3

• Cu6Sn5

• Ag3Sn

Answer explanation

Sn7-8Hg is Gamma 2

Ag2Hg3 is Gamma 1

Cu6Sn5 is Eta

Ag3Sn is Gamma

What percentage is Cu in a high copper alloy?

• 40-60

• 27-30

• 13-30

• 43-46

Answer explanation

High copper alloy is around 13% Cu

Which of the following is NOT a physical property of amalgam?

• Thermal conductivity

• Creep

• Electrical conductivity

• Opalescence

Answer explanation

The physical properties are thermal, electrical, and creep.

High Copper Admixed has a lower compressive strength than high copper spherical. It also has a higher creep percentage.

• True

• False

What is the max amount of creep at 4 hr according to ANSI/ADA specifications?

• 5%

• 1%

• 13%

• 6%

Answer explanation

Maximum allowable is 1% in case of a low Cu amalgam.

One issue with Zinc-containing amalgam is it’s delayed expansion when exposed to saliva.

• True

• False

Answer explanation

Presence of Zinc in the alloy produces delayed amalgam expansion if fluids are present.

A solution to this is the use of isolation or zinc-free alloys.

Which is NOT a disadvantage of dental amalgam?

• Unaesthetic

• Allergy

• Galvanic effect

• Short life span of material

Answer explanation

Longevity is actually an advantage of amalgam. It can last from 20-25 years ideally or at least 10 years.

What is the OSHA maximum threshold limit value for vaporized Hg?

• 50 ug/m^3

• 3 ug/m^3

• 35 ug/m^3

• 33 ug/m^3

Methyl Mercury is an example of:

• Elemental Hg

• Hg Vapor

• Inorganic Hg

• Organic Hg

Answer explanation

Methyl mercury is an example of organic Hg which you can get from eating fish.

Hg vapor is elemental.