Amalgam

Question 1

what is the composition of traditional amalgam?

6

Answer 1

powder - silver, tin, copper, zinc, mercury
liquid - mercury

Question 2

what is the function of the constituents of traditional amalgam?

6

Answer 2

silver/tin - gamma phase, reacts with liquid Hg to form amalgam
copper - increases strength and hardness
zinc - reacts with oxygen
mercury powder - accelerate the tting reaction
mercury liquid - very pure and reacts with metals

Question 3

what are the different particle types? how are they formed? and describe them

2

Answer 3

lathe cut - coarse, medium, fine, formed by filing ingots
spherical - range of sizes, formed by spraying molten metal into inert atmosphere

Question 4

what is the setting reaction of amalgam in simple terms?

Answer 4

Ag3Sn(γ) + Hg -> Ag3Sn(γ) + Ag2Hg3(γ1) + Sn7Hg9(γ2)

Ag2Hg3(γ1) + Sn7Hg9(γ2) is the amalgam matrix

Question 5

describe each gamma phase in amalgam’s structure

3

Answer 5

γ - good strength and corrosion resistance
γ1 - good corrosion resistance
γ2 - weak and poor corrosion resistance

γ1 holds γ and γ2 together

Question 6

what is the difference in setting dimensional changes with traditional and modern mixed amalgams?

Answer 6

traditional amalgam initially contracts then expands
modern amalgam contracts a small amount then maintains it

traditional = hand mixed, modern = mechnically mixed

Question 7

why is zinc used less in amalgam?

Answer 7

interacts with saliva/blood
* Zn + H2O -> ZnO + H2
bubbles of H2 formed within amalgam
* pressure build up causes expansion
* downward pressure causes pulpal pain

Question 8

what are the advantages of spherical particles?

5

Answer 8

less Hg required
higher tensile strength
higher early compressive strength
less sensitive to condensation
easier to carve

Question 9

what factors decrease the strength of amalgam?

5

Answer 9

undermixing
too high Hg content after condensation
too low condensation pressure
slow rate of packing - increments don’t bond
corrosion

Question 10

what is creep?

Answer 10

when a material experiences low-level stresses that are applied repeatedly over a period of time

Question 11

is amalgam biocompatible?

Answer 11

yes because there is no evidence that it harms humans

Question 12

what are the thermal properties of amalgam?

Answer 12

thermal expansion - 3x greater than tooth tissue
thermal conductivity - high so may need a liner in deep cavities
thermal diffusivity - high so when a thermal stimuli is applied, amalgam’s temperature rises quickly and can damage the pulp

Question 13

what is used to mix amalgam? describe it

Answer 13

amalgamator/capsule mixer
* capsule is loaded with amalgam powder and liquid mercury separated by a membrane
* once started, membrane is punctured and ultrasonic vibrations ensure even mixing

Question 14

what can provide the conditions for corrosion of amalgam?

3

Answer 14

saliva, pH changes, drinks consumption

Question 15

how do you decrease amalgam’s corrosivity?

Answer 15

copper enriched, polished margins
avoiding galvanic cells

Question 16

what are the different types of copper enriched amalgam?

2

Answer 16

dispersion modified
single composition types

Question 17

what is the composition of dispersion modified copper enriched amalgam?

Answer 17

• Ag-Cu spheres added to conventional lathe cut alloy
• γ and γ1 particles present
• Cu6Sn5 forms a halo around Ag/Cu spheres
• all γ2 is consumed so less corrosive

Question 18

what is the setting reaction for dispersion modified copper enriched amalgam?

Answer 18

1. γ + Hg -> γ + γ1 + γ2
2. γ2 + Ag-Cu -> Cu6Sn5 + γ1

Question 19

what is the composition of single composition copper enriched amalgam?

Answer 19

powder Ag - Sn - Cu
liquid Hg
particles are lathe cut or spherical

Question 20

what is the setting reaction for single composition copper enriched amalgam?

Answer 20

Ag-Sn-Cu + Hg -> Ag-Sn-Cu + γ1 + Cu6Sn5

Question 21

what are the benefits of copper enriched?

4

Answer 21

stronger at early stages and in long term
less creep
higher corrosion resistance
increased durability of margins

Question 22

what are the advantages of amalgam?

5

Answer 22

strong
hard
durable
radiopaque
user friendly

Question 23

what are the disadvantages of amalgam?

4

Answer 23

corrosion
leakage - doesn’t bond to tooth
poor aesthetics
mercury - toxic

Question 24

what are the properties of amalgam?

13

Answer 24

• high strength
• high abrasion resistance
• susceptible to creep
• setting shrinkage
• thermal expansion
• high thermal conductivity
• high thermal diffusivity
• corrosive
• biocompatible
• poor aesthetics
• radiopaque
• not anticariogenic
• smooth surface if polished but can deteriorate