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Direct Restoration > Fall Lecture 1: Dental Amalgam: Physical and Mechanical Properties, Composition, and Handling > Flashcards

Fall Lecture 1: Dental Amalgam: Physical and Mechanical Properties, Composition, and Handling Flashcards

1
Q

Alloy:

A

2 or more metals to give greater strength or resistance to corrosion, 2 or more metals with non-metals

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2
Q

2 examples of alloys:

A

bronze, brass

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3
Q

Bronze:

A

copper, tin, and other metals (aluminium, etc.) and non-metals such as arsenic, phosphorus, or silicon

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4
Q

Brass:

A

copper, zinc

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5
Q

Dental amalgam alloy:

A

silver, tin, copper, zinc

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6
Q

Which metal is kept separate from the rest in the amalgam capsules?

A

mercury

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7
Q

Dental amalgam alloy:

A

silver, tin, copper, mercury (may also contain: zinc, palidium)

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8
Q

When does dental amalgam become an amalgam?

A

when it mixes with mercury

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9
Q

3 types of dental amalgam alloy:

A

Conventional lathe-cut alloy, spherical alloy, admix alloy (mixture of lathe-cut and spherical particles)

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10
Q

Formulation of alloy we use is based on:

A

what G.V. Black Presented in 1885

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11
Q

How did dental alloys change in the 60’s?

A

high copper content and spherical particles

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12
Q

Lathe-cut alloys:

A

irregularly shaped particles produced by milling or lathe cutting of cast of _?___ amalgam alloy

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13
Q

Spherical alloys:

A

made in a gas chamber, less mercury than lathe cut = better props, low mercury helps the spherical powder, smaller volume ratio than lathe powder

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14
Q

Alloys w buttery/soft consistency:

A

spherical

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15
Q

Issue with filing Class 2 resto with spherical alloy:

A

buttery, soft, very plastic, good proximal (Class 2) contact can be tough to get, need great clinical technique

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16
Q

Why can spherical be used for core build up material?

A

high early strength, strong after 10-15m

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17
Q

Which have higher final strength, admix alloys or spherical alloys?

A

spherical, core build up must be strong

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18
Q

Benefit of admix:

A

denser final amalgam

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19
Q

Most common material in dental amalgam:

A

admix alloy

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20
Q

Admix alloy requires:

A

more force, better for proximal contacts, stregnth is time dependent, initially relatively weak, delay final polishing at least 24h

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21
Q

These alloys have low copper:

A

lathe-cut and spherical

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22
Q

These alloys have high copper:

A

admix and spherical

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23
Q

Does spherical have low or high copper?

A

can be either

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24
Q

Silver provides:

A

strength

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25
Q

Fxn of tin in amalgam:

A

dec expansion

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26
Q

Composition of dental amalgam, high to low:

A

Ag, Sn, Cu, Zn (STCZ)

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27
Q

TF? It is important that the amalgam expand after it is set.

A

F. should not expand (tin)

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28
Q

Copper fxn:

A

strength, (low to high range)

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29
Q

Low copper percentage:

A

3%

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30
Q

High copper

A

up to 30%

31
Q

Copper decreases corrosion by:

A

decreasing gamma 2 phase

32
Q

What eliminates the gamma 2 phase?

A

copper

33
Q

Zinc fxn:

A

scavenger, deoxidizer during melting, inc plasticity, more susceptible to moisture contamination, delayed expansion

34
Q

TF? Zn free amalgam is better, than with Zn.

A

F.

35
Q

These alloys are brittle and difficult to blend uniformly

A

sliver/tin alloys (copper replaces the silver to increase strength)

36
Q

First silver/copper alloy was made in:

A

early 60’s

37
Q

Silver/ copper alloy is aka:

A

dispersed phase or admix high-copper alloy

38
Q

Amalgam we use:

A

Valiant PHD XT, phase dispersed (Ivoclar Vivadent), low mercury, high copper, extended stetting time (7-10min)

39
Q

State of the art amalgam:

A

high copper amalgam

40
Q

% Cu required to be a high copper amalgam:

A

9-30%

41
Q

Benefits of high copper amalgam:

A

inc strength and marginal integrity, elimination of gamma 2 phase

42
Q

Is an 8% copper amalgam considered a ‘high copper’ amalgam?

A

no

43
Q

Why does high copper amalgam perform the best in clinic?

A

elimination of gamma 2 phase

44
Q

Gamma phase:

A

unreacted particles (sliver, tin particles, strong, suspended in matrix of gamma 1 phase, reaction product of silver and mercury, less strong and more corrosion susceptible (?)

45
Q

Which amalgam reaction has a gamma 2 phase?

A

conventional or low copper amalgam reaction, weakest, most corrosion susceptible phase

46
Q

Phases, strong to weak:

A

gamma, 1, then 2

47
Q

If a tin/mercury compound is present is this low copper or high copper reaction?

A

low copper

48
Q

What compound is eliminated with the elimination of the gamma 2 phase?

A

Sn7Hg (weakest compound eliminated, high copper reaction stronger)

49
Q

Low copper amalgam development:

A

dissolution, precipitation of g1 crystals, Hg consumption and growth of g1 and g2, final set

50
Q

Greater unconsumed silver tin will lead to greater/decreased strength:

A

greater

51
Q

Creep:

A

low creep, better restoration, time dependent deformation due to stress on material (high Cu amalgam: improved marginal integrity, decreased breakdown in margin, less creep)

52
Q

Amalgams w delayed expansion after moisture contamination:

A

zinc-containing amalgams, tin helps to reduce expansion (wks to mths)

53
Q

___ gas causes the restoration to expand after wks to mths

A

hydrogen

54
Q

When to use zinc-free amalgam?

A

moisture control difficult

55
Q

compressive strength of amalgam, high or low?:

A

very high

56
Q

tensile and shear strength of amalgam are higher/lower than its compressive:

A

lower

57
Q

Tarnish:

A

amalgam surface is dulled or discolored, formation of oxide layers

58
Q

Corrosion

A

actual deterioration of a metal, chemical rxn bw metal and env (H20, air, saliva) forming metal compounds or corrosion products

59
Q

Zinc works as:

A

scavenger, deoxidizes

60
Q

increase tin:

A

increase tarnish and corrosion

61
Q

Increased copper

A

decrease tarnish and corrosion

62
Q

percolation of amalgam:

A

influx of salivary fluid bw microscopic gap bw resto and tooth

63
Q

High copper amalgams have fast/slow rate of percolation:

A

slow, no g2 phase in high copper amalgam

64
Q

this phase corrodes the most

A

g2 phase

65
Q

Percolation takes (this long) in high copper amalgams:

A

6 mo

66
Q

These metals have all the opposite effects as each other:

A

Sn and Cu

67
Q

Effects of Sn:

A

dec strength, dec setting expansion, inc creep, inc flow, dec compressive strength, inc tarnish and corrosion

68
Q

Which metal has all the same properties as Cu except for tarnish and corrosion?

A

Ag

69
Q

Which amalgam has more copper?

A

admix

70
Q

What causes the delayed expansion?

A

zinc

71
Q

What reduces the oxide layer?

A

zinc

72
Q

__ increases corrosion, while __ decreases corrosion:

A

tin, copper

73
Q

This helps to create self sealing:

A

percolation

74
Q

This is (basically) the corrosive phase:

A

g2 phase

Direct Restoration (23 decks)

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