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Dental Materials > Amalgam > Flashcards

Amalgam Flashcards

1
Q

Why use amalgam

A 
Inexpensive
Easy to use
>100 yr history
Familiarity
Resin free this less allergies
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2
Q

What are the basic constituents of amalgam

A

Silver
Tin
Copper
Mercury

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3
Q

How does silver affect amalgam

A

Increases strength and expansion

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4
Q

How does tin affect amalgam

A

Decreases expansion, strength

Increases setting time

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5
Q

How does addition of copper affect amalgam

A 
Ties up tin
Decreases gamma 2
Increases strength
Reduces tarnish and erosion
Reduces creep (marginal deterioration)
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6
Q

What does mercury do for amalgam

A
  • activates reaction

- liquid at room temp

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7
Q

do spherical alloys require more or less mercury than admixed

A

spherical less (45 vs 50%) because they have smaller surface area and are easier to wet

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8
Q

Why is zinc sometimes used in amalgam

A

Decreases oxidation of other elements and less marginal breakdown

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9
Q

Palladium does what to amalgam

A

reduce corrosion

greater luster

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10
Q

What amalgam that we use has palladium

A

Valiant PhD

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11
Q

How much mercury is mixed with alloy

A

50/50

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12
Q

What are the three particle shapes for amalgam

A

lathe cut, spherical, admix

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13
Q

Tytin have what particle shapes

A

spherical

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14
Q

Dispersalloy, Original D, and Valiant PhD has what type of particle shape

A

admix

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15
Q

In amalgam equations what is gamma

A

the unreacted Alloy

forms 30% of volume of set amalgam

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16
Q

What is gamma 1

A

2nd strongest
60% of volume
Ag2Hg3
creates matrix around unreacted alloy

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17
Q

gamma 2

A

weakest and softestphase
Sn8Hg
as corrodes over time Hg is released which reacts with the alloy so volume of gamma 2 decreases over time

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18
Q

Describe admix alloy componets

A 
2 types of particles spherical and lathe cut
spherical Ag-Cu
lathe cut
AG SN
The copper ties up the tin
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19
Q

How do single composition high copper alloys differ

A

the gamma spheres have a copper tin coating that reduce creep and prevents gamma 2 formation

20
Q

What dimensional change do high copper amalgams undergo

A

net contraction
.3% shrinkage
contraction leaves marginal gap but is reduced overtime with corrosion

21
Q

What factors affect amalgam contraction

A

type of alloy:spherical have more due to less hg
condensation+more condensation + greater contraction
trituration time
more trituration causes higher contraction

22
Q

Amalgam strength variables

A

Time: at 1 hr 40-60% at 24 hrs 90%
Spherical alloys strengthen faster
need bulk for strength. Brittle at thinner sections

23
Q

How does corrosion affect amalgam restorations

A

Reduces strength
acts to seal margins
low copper 6months
high copper up to 24 months

24
Q

Which kinds of Am have been shown to last longest? Shortest

A

Shortest
low copper zinc free
longest
high copper with zinc

25
Q

Describe an overtrituated mix

A

hot
decreased setting time
increased contraction

26
Q

Describe an undertriturated mix

A

grainy and crumbly

27
Q

What kind of condensation forces do you use on lathe cut

A

small condensers with high force

28
Q

what kind of condensing do you use for spherical

A

large condensers using vertical/lateral vibratory motion

29
Q

how do you condense admix

A

intermediate between spherical and lathe cut

30
Q

Why should you burnish amalgams and when should you

A

pre carve to remove excess Hg and improve margin
post car to improve smoothness
doing both gives less leakage

31
Q

Does polishing improve marginal integrity

A

Collins J Dent 92 say no

32
Q

What are the advantages of spherical alloys

A

Easier to condense
hardens rapidly
smoother polish

33
Q

what are the disadvantages of spherical alloy

A

hardens rapidly
hard to get tight proximal contacts
higher tendency for overhang
higher shrinkage

34
Q

what are the advantages of admixed

A

easy to achieve tight contacts
good polish
hardens slowly

35
Q

What are the disadvantages of admix

A

hardens slowly with lower early strength

36
Q

Should we bond amalgam?

A

Cochrane: No difference in Am survival or post op sensitivity
summit 2004: bonded complex am were as retentive as using pins
conclusion: Probably only use for complex

37
Q

whats the avg daily dose from 8-10 Am surfaces of mercury

A

1-2 micrograms

38
Q

What are the threshold mercury levels for pre clinical effects and dangerous effects

A

preclinical 30micrograms

dangerous 80 micrograms

39
Q

what is the biologic activity of mercury

A

binds to sulfhydryl groups

no carcinogenicity but can cause birth defects

40
Q

what form of mercury is most toxic

A

alylmethyl

minimal bay japan posoning

41
Q

when removing Am how does the Hg vapor release compare to the established exposure level threshold

A

far below, < 5%

42
Q

any evidence to link Am to diseases

A

nope

43
Q

what is the exa ruling on Am

A

install am separators to reduce Am entering sewer
prohibit use of oxidizing agents for flushing of vacuum systems
prohibit rinsing or flushing of Am waste down a drain

44
Q

Whats the minimata convention

A

Global agreement to protect human health from releases of Hg. Phase down use of Am

45
Q

What does the ban on Am do to Dental Economics

A

Increase res price ~19%
decrease number of res placed
increase in untreated car

Dental Materials (9 decks)

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