Test One: Dental Amalgam

Question 0

What is the composition of dental amalgam?

Answer 0

Silver alloy (Ag, Sn, Cu) and amalgam

Question 1

Two types of amalgam

Answer 1

Low copper alloys (13%); spherical or admix, sets faster, gamma2 converted to eta

Question 2

How does indium affect the alloy?

Answer 2

Decreases surface tension–increases wettibility which reduces need for Mercury, also reduces creep and breakdown while increasing strength

Question 3

How does palladium affect the alloy?

Answer 3

Reduces corrosion and increases luster

Question 4

What alloy shape sets the fastest?

Answer 4

Spherical (Tytin)

Question 5

Low copper rxn

Answer 5

Ag3Sn (gamma)+ Hg –> Ag3Sn+ Ag2Hg3 (gamma1)+ Sn7-8Hg (gamma2)

Question 6

High copper rxn

Answer 6

Start with original low copper rxn, then adding additional copper phase to get rid of gamma2
Sn7-8Hg (gamma2) + AgCu (eutetic) –> Cu6Sn5 (eta)+ Ag2Hg3 (gamma1)

Question 7

Why is copper added to the amalgam?

Answer 7

To decrease the amount of gamma2 (which is weak, corrosion prone, and leads to marginal breakdown)

Question 8

How is copper added?

Answer 8

Separate particle of Ag3Cu2 – eutectic (65 wt% Ag, 35% Cu) that is spherical in shape, or Add Cu to existing alloy particle

Question 9

What factors affect rate of amalgamation?

Answer 9

Trituration time and force, particle shape, and type of Cu addition

Question 10

What affects compressive strength?

Answer 10

Resistance form, spherical particles with high copper have the highest final strength and the fastest increase in strength over time

Question 11

How does tensile strength compare between dispersalloy and tytin?

Answer 11

Tensile strength increases more slowly and is overall lower for dispersalloy

Question 12

What do negative and positive dimensional change lead to?

Answer 12

Negative–>marginal leakage

Positive–>pain/fracture

Question 13

What can cause corrosion of amalgam?

Answer 13

Multiple phases, gamma 2 continuous phase

Question 14

How does corrosion affect an amalgam restoration?

Answer 14

Positive- can help with initial marginal seal

Negative- degradation of restoration

Question 15

Signs/ symptoms of mercury toxicity

Answer 15

Paresthesia, ataxia, joint pain, death

Question 16

Mercury exposures from the environment

Answer 16

Water: .05 inorganic
Air: .192 total
Fish: 4.7 total
Food: 20 inorganic
Amalgam: 1-2 elemental

Question 17

What are the risks for Mercury exposure for patients and staff?

Answer 17

Patient has very low exposure mainly during manipulation

Staff has a higher exposure risk because of daily use but no evidence of harm

Question 18

How to limit exposure in dental office

Answer 18

– use high vol vacuum during procedures
– cut wet, NEVER dry
– use a rubber dam
– close amalgamator cover when mixing
– NO ultrasonic condensers
– store scrap properly (under fixer, cool place) – NO TOUCH TECHNIQUE (even with gloves)