dental amalgam Flashcards Preview

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Flashcards in dental amalgam Deck (28):
1

What is the product of amalgamation?

alloy and mercury react to form silvery hard grey mass

2

why is the used of amalgam declining?

development of viable alternatives
concerns re. safety- mercury

3

what composition of amalgam was before 1896?

conventional amalgam

4

What composition post 1896?

high copper amalgam

5

What metals make up amalgam alloy?

Ag, Sn,Cu,Zn, Hg

6

What types of variations re. alloy morphology?

lathe cut
spherical

7

what element has strengthening effect on amalgam?

Cu

8

What element acts as scavenger in alloy production?

Zn

9

The setting reaction happens mostly on what element?

Ag3Sn

10

What dimensional changes occur in the first 30 minutes?

small shrinkage
Hg diffuses into alloy

11

What dimensional changes occur 30-60 minutes?

expansion- due to crystalisation

12

What is the overall effect of the amalgam setting reaction?

net expansion/contraction

13

What is the ISO limit of expansion and contraction?

0.1%

14

How long after placement is the restoration functional?

15-20 minutes

15

what long till restoration reaches final strength?q

24 hours

16

When is strength optimum?

When Hg is 44-48%

17

What helps to achieve optimum strength?

correct manipulation of material
removing mercury rich layer

18

What is creep?

plastic deformation under load
protrusions at restoration margins

19

What stage is largely responsible for creep?

gamma 2

20

what exacerbates creep?

corrosion of alloy
release of Hg in marginal crevice

21

What is corrosion?

electrochemical interaction of different alloy phases with saliva as electrolyte

22

What do products of corrosion do?

provide marginal seal

23

When is corrosion highest?

in high copper phase
gamma 2

24

What has mercury content of amalgam been linked to?

MS
Behavioural problems
Psychiatric disturbances

25

What aspects are of concern re. environmental pollution?

water of dental unit
release of Hg during trituration
crematoria

26

What techniques remove excess mercury?

packing and condensing

27

What does smaller particle of alloy achieve?

higher 1 and 24 hour strengths

28

What are the down sides to too small particles?

too rapid set
not enough working time to remove excess Hg