Dental Amalgam

Question 1

what is amalgam?

Answer 1

mixture of any metal/alloy with mercury (Hg)

Question 2

what is an amalgamation reaction?

Answer 2

the chemical reaction when mixing mercury with alloy

Question 3

dental amalgam is a mixture of what?

Answer 3

dental alloy and mercury

Question 4

advantages of dental amalgam? 3

Answer 4

high compressive strength
easy to manipulate
low cost

Question 5

disadvantages of amalgam? 3

Answer 5

poor aesthetics
potential for thermal irritation
creep

Question 6

what is creep?

Answer 6

deformation under a load over time

Question 7

what are the two compositions of dental amalgam?

Answer 7

conventional
high copper

Question 8

what are the major components of dental amalgam? 5

Answer 8

silver Ag
tin Sn
copper Cu
zinc Zn
mercury Hg

Question 9

what is the differences between the setting reaction of conventional and high copper dental amalgam?

Answer 9

absence of gamma 2 phase in high copper (tin-mercury)
replaced with copper-tin phase

Question 10

what effect does copper have on dental amalgam?

Answer 10

it has a strengthening effect

Question 11

what is the purpose of zinc in the setting reaction of dental amalgam?

Answer 11

prevents oxidation of the alloy during melting

Question 12

what does trituration mean?

Answer 12

mixing

Question 13

what is happening for the 1st 30mins of the setting reaction to dental amalgam?

Answer 13

small shrinkage while Hg diffuses into the alloy

Question 14

what is happening between 30 and 60 mins?

Answer 14

expansion due to crystallisation

Question 15

what is important to control during the setting reaction of dental amalgam?

Answer 15

moisture control

Question 16

what dimensional changes occur to the setting reaction of amalgam if moisture contaminates the zinc containing alloy?

Answer 16

delayed expansion due to liberation of Hydrogen

larger expansion

Question 17

the strength of dental amalgam develops fast or slow

Answer 17

slowly

Question 18

dental amalgam is relatively weak in the first ?-?mins

Answer 18

15-20

Question 19

it can take up to how many hours for dental amalgam to become high strength?

Answer 19

24hrs

Question 20

dental amalgam has a better transverse, compressive or tensile strength?

Answer 20

compressive

Question 21

where is dental amalgam weak?

Answer 21

thin sections

Question 22

what are 2 possible effects of excessive creep?

Answer 22

ditching
gingival overhangs

Question 23

what is the most corrodible phase of dental amalgam setting reaction? what happens?

Answer 23

gamma 2 breaks down into Hg and tin that are free and ingested

in high copper tin and copper and free

Question 24

what can inhibit the corrosion process of dental amalgam?

Answer 24

phosphate buffer solution so saliva may provide protection

Question 25

dental amalgam has high thermal conductivity. what can protect the pulp from thermal irritation

Answer 25

an insulating lining material

Question 26

placement and removal of dental amalgam is banned for what patients?

Answer 26

pregnant

Question 27

how does the particle size of the alloy effect dental amalgam?

Answer 27

smaller means higher 1 & 24hr strengths
if extremely small too rapid set -> cant remove excess Hg -> inferior properties

Question 28

how does alloy particle shape effect dental amalgam?

Answer 28

if lathe-cut (irregular) - requires more Hg to achieve plasticity

if spherical (regular) - needs less Hg than lathe-cut thus superior properties