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Dental Materials > dental amalgam > Flashcards

dental amalgam Flashcards

1
Q

What is the product of amalgamation?

A

alloy and mercury react to form silvery hard grey mass

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2
Q

why is the used of amalgam declining?

A

development of viable alternatives

concerns re. safety- mercury

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3
Q

what composition of amalgam was before 1896?

A

conventional amalgam

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4
Q

What composition post 1896?

A

high copper amalgam

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5
Q

What metals make up amalgam alloy?

A

Ag, Sn,Cu,Zn, Hg

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6
Q

What types of variations re. alloy morphology?

A

lathe cut

spherical

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7
Q

what element has strengthening effect on amalgam?

A

Cu

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8
Q

What element acts as scavenger in alloy production?

A

Zn

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9
Q

The setting reaction happens mostly on what element?

A

Ag3Sn

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10
Q

What dimensional changes occur in the first 30 minutes?

A

small shrinkage

Hg diffuses into alloy

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11
Q

What dimensional changes occur 30-60 minutes?

A

expansion- due to crystalisation

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12
Q

What is the overall effect of the amalgam setting reaction?

A

net expansion/contraction

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13
Q

What is the ISO limit of expansion and contraction?

A

0.1%

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14
Q

How long after placement is the restoration functional?

A

15-20 minutes

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15
Q

what long till restoration reaches final strength?q

A

24 hours

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16
Q

When is strength optimum?

A

When Hg is 44-48%

17
Q

What helps to achieve optimum strength?

A

correct manipulation of material

removing mercury rich layer

18
Q

What is creep?

A

plastic deformation under load

protrusions at restoration margins

19
Q

What stage is largely responsible for creep?

A

gamma 2

20
Q

what exacerbates creep?

A

corrosion of alloy

release of Hg in marginal crevice

21
Q

What is corrosion?

A

electrochemical interaction of different alloy phases with saliva as electrolyte

22
Q

What do products of corrosion do?

A

provide marginal seal

23
Q

When is corrosion highest?

A

in high copper phase

gamma 2

24
Q

What has mercury content of amalgam been linked to?

A

MS
Behavioural problems
Psychiatric disturbances

25
Q

What aspects are of concern re. environmental pollution?

A

water of dental unit
release of Hg during trituration
crematoria

26
Q

What techniques remove excess mercury?

A

packing and condensing

27
Q

What does smaller particle of alloy achieve?

A

higher 1 and 24 hour strengths

28
Q

What are the down sides to too small particles?

A

too rapid set

not enough working time to remove excess Hg

Dental Materials (13 decks)

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