Amalgam

Question 1

With time, amalgam ___(expands or shrinks?) and composite ____ (expands or shrinks?)

Answer 1

With time, amalgam expands and composite shrinks (polymerization shrinkage)

Question 2

Major uses of amalgam

Answer 2

• Direct restorations
• core build up
• retrograde restorations

Question 3

Why is amalgam better over time?

Answer 3

• Because it expands (Creates natural sealing of the restoration)
• It corrodes over time, but this can be beneficial because corrosion products fill microgaps and prevent leakage)
• Contains silver, which is bacteriostatic (stops process of carie by killing bacteria)

Question 4

Amalgam is an alloy containing ___ as the major ingredient

Answer 4

Hg (mercury)

Question 5

Dental amalgam is an alloy of ___ with ____

Answer 5

Hg with Ag-Sn

Question 6

In the following reaction, what is the dental amalgam alloy?:

Dental amalgam alloy + mercury __> dental amalgam

Answer 6

Ag-Sn alloy

Question 7

What materials in amalgam provide mechanical reinforcement and better corrosion resistance?

Answer 7

The UNREACTED ALLOY particles which are embedded within the matrix.
More matrix = weaker
More filler = stronger

Question 8

What effect does a greater concentration of silver in dental amalgam have on the final product?

Answer 8

More silver = greater expansion.

Too much silver could cause tooth breakage.

Question 9

What is the ideal ratio of silver to tin in dental amalgam to avoid breakage?

Answer 9

3 atoms of silver to 1 of tin:
Ag3Sn
THE EXPANSION OF SILVER IS COUNTERBALANCED BY THE CONTRACTION OF TIN.

Question 10

two major types of amalgam

Answer 10

• low copper amalgam <6%

- High copper amalgam >6%

Question 11

Approximate composition of an acceptable amalgam alloy according to the ADA

Answer 11

-min 65% silver
-max 29% tin
-max 6-13% copper
max 2% zinc by weight

Question 12

Properties of Ag in amalgam

Answer 12

Ag is the main constituent in amalgam. Provides STRENGTH, DURABILITY, CORROSION RESISTANCE, color, INCREASES SETTING EXPANSION, DECREASES FLOW, and DECREASES SETTING TIME

Question 13

Properties of Sn in amalgam

Answer 13

Compensates for expansion of silver, makes amalgam easier to work, increases flow and setting time, DECREASES STRENGTH AND CORROSION RESISTANCE

Question 14

Properties of Cu in amalgam

Answer 14

Increases strength, hardness, corrosion resistance, CONTRIBUTES TO SETTING EXPANSION, reduces flow, and decreases setting time. Hardest metal in amalgam

Question 15

Properties of Zn in amalgam

Answer 15

Increases workability, unites with oxygen and other impurities to produce CLEAN AMALGAM.
WATER MAY REACT WITH ZN TO PRODUCE EXPANSION ZnO and H2 gas.
“amalgam janitor.” Takes oxidation for itself and “saves” silver

Question 16

What effect does silver have on the strength of amalgam?

Answer 16

increases

Question 17

What effect does silveer have on the durability of amalgam?

Answer 17

increases

Question 18

What effect does Copper have on hardness of amalgam?

Answer 18

increases

Question 19

What effect do silver, tin and copper have on the expansion of amalgam?

Answer 19

Silver: increases
Tin: decreases
Copper: increases

Question 20

What effect do silver, tin and copper have on the flow of amalgam?

Answer 20

Silver: decreases
Tin: increases
Copper: decreases

Question 21

What affect do silver, tin and copper have on the setting time of amalgam?

Answer 21

Silver: decreases
Tin: increases
Copper: decreases

Question 22

What affect do tin and zinc have on the workability of amalgam?

Answer 22

Tin: increases
Zinc: increases

Question 23

What effect does zinc have on the cleanliness of amalgam?

Answer 23

Increases. It saves silver from oxidation by taking it for itself instead

Question 24

3 microstructure types of amlgam and their descriptions

Answer 24

Lathe cut: irregular particles. Require more mercury to cover surface, ie. more matrix = less mech properties.
Spherical: Less mercury leading to better mech properties. However, difficult to achieve condensation.
Admixed: Most used today. Mixed spherical and irregular particles. The irregular particles pack together better

Question 25

Classifications of amalgam

Answer 25

Classified by:

• COPPER CONTENT (high or low)
• PARTICLE SIZE AND SHAPE (irregular, spherical)
• ZINC CONTENT (Zn-containing, Zn free)

Question 26

What composes the matrix of amalgam?

Answer 26

excess mercury (Hg)

Question 27

How is excess Hg-rich matrix eliminated?

Answer 27

by condensation

Question 28

Low-copper amalgam setting reaction

Answer 28

Ag3Sn + Hg --> Ag3Sn + Ag2Hg3 + Sn7Hg
ie.
Powder + liquid --> unreacted alloy + amalgam matrix
ie.
gamma + Hg --> gamma + gamma-1 +gamma-2

Question 29

Weakest phase in amalgam matrix?

Answer 29

gamma-2

Question 30

High-copper dental amalgam reaction

Answer 30

Ag3Sn + Hg –> Ag3Sn + Ag2Hg3/Cu + CuSn + Cu3Sn
ie.
gamma + Hg –> gamma + gamma-1 + E + n
THIS RXN ELIMINATES GAMMA-2

Question 31

Ways to reduce gamma-2 phase (Sn7Hg)

Answer 31

• lower final amalgam Hg content
• Proper condensation techniques
• Add Copper

Question 32

Dimensional changes in amalgam

Answer 32

• CONTRACTION during alloy dissolution
• EXPANSION during reaction, crystal formation
• EXPANSION due to H2O contamination

Question 33

Physical properties of amalgam:

1. thermal conductivity
2. electrical conductivity
3. coefficient of thermal expansion
4. radiopacity
5. Color

Answer 33

Physical properties of amalgam:

1. thermal conductivity: HIGH
2. electrical conductivity: HIGH
3. coefficient of thermal expansion: 25 ppm/C (double that of a tooth)
4. radiopacity: RADIOPAQUE
5. Color: LUSTROUS, SHINY, WHITE