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BDS2.5 Dental Materials - operative dentistry > Dental Amalgam > Flashcards

Dental Amalgam Flashcards

1
Q

What is amalgam?

A

alloy + mercurary

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2
Q

What is dental amalgam?

A

alloy containing silver, tin and certain elements and mercury

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3
Q

What is the reaction of alloy and mercury called?

A

amalgamation

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4
Q

What is the predominant element in alloy?

A

silver

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5
Q

What does silver combine with?

A

tin, the main reaction

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6
Q

Why is mercury added?

A

increase rate of reaction - pre-amalgamation

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7
Q

What does zinc preferentially react with?

A

oxygen

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8
Q

What would you call an alloy with less than 0.01% zinc?

A

zinc free alloys

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9
Q

What percent are zinc containing alloys?

A

more than or equal to 0.01%

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10
Q

When does zinc produce hydrogen gas?

A

when reacted with water

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11
Q

Why is moisture control important (specifically with zinc)?

A

zinc reacts with water to produce hydrogen gas and excessive delayed expansion

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12
Q

Do the majority of alloys have zinc?

A

no

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13
Q

What form of mercury is used and why?

A

pure form otherwise inferior physical properties result

adversely affect the setting characteristics of the amalgam

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14
Q

Is mercury distilled?

A

yes, 3 times

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15
Q

What is the appearance of contaminated mercury?

A

dull appreance - we know encapsulate

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16
Q

What are the 3 phases of amalgamation? (mercury with alloy)

A
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17
Q

What is the unreacted core surrounded by?

A

amalgam matrix

(gamma 1 silver/mercury and gamma 2 tin/mercury)

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18
Q

What depth of the outer layer react with alloy particles?

A

3-5 um

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19
Q

What is gamma 1?

20
Q

What is the gamma 2 phase?

A

tin-mercury phase

21
Q

What is the most critical phase?

A

gamma 2 phase

22
Q

What are the features of the gamma 2 phase?

A

most chemically electrically active component

physical properties inferior to gamma and gamma 1 phases

more prone to corrosion

poor tensile strength

23
Q

What phases are the green, purple and blue in the amalgam?

A

green = gamma 1 (silver/mercury)
purple = gamma 2 (tin/mercury)
blue = gamma (silver/tin)

24
Q

What is tensile strength?

A

ability of a material to withstand pulling forces in an axial direction

25
Q

What shape do you test tensile strength on?

26
Q

What is creep?

A

gradual dimensional change under load

27
Q

What phase is more susceptible to creep?

28
Q

What can creep lead to?

29
Q

What is ditching?

A

the amalgam has move over time, thinned out at the margin - can chip

creates channels called a ditch

30
Q

What is the percent of creep with amalgam?

31
Q

What does high copper amalgams attempt to eliminate?

A

gamma 2 phase

32
Q

What percent is high copper amalgams?

A

above 13% content

33
Q

What is the result of high copper amalgams?

A

higher mechanical strength properties

more rapid set to full strength

reduction in creep

reduced susceptibility to corrosion

34
Q

What is compressive strength?

A

ability of a material to withstand axially loaded pushing forces (applied along long axis)

35
Q

What are the setting reactions of high copper dental amalgam?

A

essentially the same as conventional alloys

36
Q

In high copper amalgam setting reactions, what phase has little to nothing left in the final amalgam?

37
Q

In high copper amalgam, what 2 thing preferentially react?

A

copper and tin

38
Q

What complex is formed in the high copper amalgam setting reaction?

A

silver-tin-copper complex

little to no gamma 2 left

39
Q

In high copper amalgam, hat surrounds the silver/tin/copper complex?

A

copper/tin

40
Q

What are the types of high copper amalgam alloy?

A

dispersed phase

ternary alloys

41
Q

Describe the dispersed phase of high copper amalgam alloy?

A

copper dispersed throughout the alloy

alloy particles either contain silver-tin or silver-copper

silver content may be kept the same as conventional alloys

increased strength

42
Q

Describe ternary alloys (high copper content amalgam alloy)

A

contain 3 elements usually silver, tin and copper all in one particle

compositional

43
Q

What is the effect of eliminating gamma 2 in high copper alloys?

A

greater microleakage

increased postoperative sensitivity

increased risk of recurrent caries

may be overcome by bonding in situ

44
Q

What is the role of gamma 2 in amalgam?

A

corrosion product of gamma2 fill the marginal micro gap at cavity interface

decrease microleakage

45
Q

What are the 3 types of alloy?

A

lathe cut

spherical

admixed

46
Q

What is the lathe cut alloy like?

A

irregular particles produced - affects reactivity with mercury

blend various particle sizes to reduce reactivity

47
Q

What is admixed alloys like?

A

combination of irregular and spherical particles

sometimes called blended

BDS2.5 Dental Materials - operative dentistry (22 decks)

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