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Dental Materials > Dental Amalgam > Flashcards

Dental Amalgam Flashcards

1
Q

What is dental amalgam?

A

an allow mixed with mercury

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2
Q

What is dental amalgam commonly used for?

A

posterior restorations

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3
Q

What is the alloy in dental amalgam made from?

A

silver
tin
copper solid particles

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4
Q

why is zinc added to dental amalgam ?

A

as a deoxidiser to make it less brittle

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5
Q

what is the composition of dental amalgam controlled by?

A

ISO standard

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6
Q

What is the setting reaction for dental amalgam?

A

set by reacting with mercury which results in phases

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7
Q

What are the dimensional changed during setting dental amalgam?

A

30 minutes - small shrinkage
30-60 minutes - expansion

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8
Q

What causes amalgam to shrink during setting?

A

mercury diffusing into the alloy

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9
Q

What causes dental amalgam to expand during setting?

A

crystallisation

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10
Q

What is the overall setting effect of dental amalgam?

A

net expansion/ contraction

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11
Q

What is the ISO limit on dental amalgam setting ?

A

+ or - 0.1% expansion/ contraction

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12
Q

At what time would you reach a functional compressive strength when setting dental amalgam?

A

15-20 minutes

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13
Q

At what time would you reach a final strength when setting dental amalgam?

A

24 hours

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14
Q

What minimum depth should be packed with dental amalgam?

A

2mm

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15
Q

How do you fill with dental amalgam?

A

in thin sections, overpack, then carve back the mercury layer

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16
Q

What happens in the particle is too small in dental amalgam?

A

too rapid a set so the mercury layer cannot be removed by manipulation

17
Q

What is plastic deformation (creep) caused by?

A

chewing/ grinding causes amalgam to flow and protrude from the cavity margin, forming edges

18
Q

What happens in low copper amalgam in the presence of saliva?

A

y2 phase breaks down and releases corrosion products and mercury

19
Q

What are advantages of corrosion products?

A

corrosion products can form a marginal seal

20
Q

Why cant pregnant woman have dental amalgam restorations?

A

mercury is toxic to the CNS

21
Q

What is the composition of conventional amalgam?

A

silver 65%
tin 29%
copper 8%
other trace metals

22
Q

What is the composition of high copper amalgam?

A

silver 40%
tin 32%
copper 30%
other trace metals

23
Q

What are the advantages of high copper dental amalgam?

A

more strength
corrosion resistance
durability
resistance to tarnish

24
Q

How is high copper amalgam cut?

A

spherical form by atomisation

25
Q

How is conventional amalgam cut?

A

cut ingots into particles

Dental Materials (9 decks)

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