Amalgam

Question 1

what are the two types of composite?

Answer 1

pre 1986 - conventional

post 1986 - high copper

Question 2

what % copper in a low copper alloy? high copper alloy?

Answer 2

low - 5%

high - 30%

Question 3

morphology of alloys?

Answer 3

lathe cut

spherical

Question 4

what happens in the amalgam setting reaction?

Answer 4

Ag3Sn undergoes setting reaction
Cu gives strengthening effect on amalgam
Zinc acts as scavenger

Question 5

trituration - ISO limit?

Answer 5

limit to +/- 0.19% expansion/contraction

Question 6

what happens with poor moisture control and a zinc alloy?

Answer 6

zinc plus water gives zinc oxide and hydrogen

Question 7

how much time between placement to function?

Answer 7

15-20 mins

Question 8

after how long does it set to its final strength?

Answer 8

24 hours

Question 9

Compressive strength is more than what?

Answer 9

the tensile strength

amalgam weak in thin sections

Question 10

Hg gives strength of?

Answer 10

44-48%

Question 11

when does creep occur?

Answer 11

when plastic deformation is under strength

Question 12

what is creep?

Answer 12

clinically - amalgam flows manifesting as protrusions at restoration margins

Question 13

what happens to amalgam as a result of creep?

Answer 13

fractures off producing ditching

Question 14

what causes creep?

Answer 14

the gamma 2 phase is largely responsible

corrosion of the alloy

Question 15

what happens during corrosion of the alloy?

Answer 15

releases Hg in marginal crevice

= localised expansion of amalgam

Question 16

what is corrosion?

Answer 16

electrochemical interactions of different alloy phases with saliva as the electroylte

Question 17

what is the gamma 2 phase?

Answer 17

gamma 2 phase is tin mercury phase = mercury free and ingested

Question 18

what do corrosion products provide?

Answer 18

marginal seal

Question 19

what phase undergoes the most corrosion?

Answer 19

high copper phase = CuSn phase

Question 20

thermal properties of amalgam?

Answer 20

high thermal diffusivity

3 fold coefficient of thermal expansion of dentine = heat in mouth is transient

Question 21

biological properties of amalgam?

Answer 21

mercury known to be toxic to CNS. High content of hg in the urine/blood of those with amalgam restorations than those without.

Question 22

links of amalgam with what conditions?

Answer 22

multiple sclerosis
behavioral problems
psychiatric disturbances

Question 23

how can mercury pollute the clinical environment?

Answer 23

water of dental unit

release of hg during trituration

Question 24

range of mercury:alloy ratio?

Answer 24

5:8 to 10:8 alloy:mercury

Question 25

how are drier mixes achieved?

Answer 25

achieved by mechanical mixing

Question 26

how to remove excess mercury?

Answer 26

packing and condensation

Question 27

dispensation of amalgam?

Answer 27

weight - most accurate - rarely used
volume dispensers
alloy tablets
proportioning/mixing devices
now is encapsulated

Question 28

smaller particle size gives?

Answer 28

higher 1 and 24 hour strengths

Question 29

extremely small particles?

Answer 29

too rapid to set