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Dental Materials > Amalgam and properties > Flashcards

Amalgam and properties Flashcards

1
Q

What are some advantages of amalgam as restorative material?

A

inexpensive, easily prepared direct material, margin sealing, longevity

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2
Q

What are some disadvantages of amalgam as restorative material?

A

poor aesthetics, weakening of tooth structure, no adhesive bonding, sensitive to manipulation, brittle, mercury waste

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3
Q

What are the two components of dental amalgam?

A

alloy + Hg

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4
Q

What is the mercury/alloy ratio?

A

0.5 or 1:2

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5
Q

What is the weight percent of mercury in an amalgam capsule?

A

42-45 wt%

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6
Q

What factors change the setting process?

A

composition, shape and size of alloy particles

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7
Q

What are the major take aways from the ADA standard No 1 requirement for amalgam?

A

composition, other elements cannot exceed 0.1 wt%,

small creep and dimensional change, and a high compressive strength

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8
Q

What are the major elements of amalgam?

A

Ag (primary), Sn (secondary), cpper, and zinc

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9
Q

What are the three phases the complex structure of the particles possess?

A

gamma (most important), beta, and epsilon

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10
Q

What is characteristic of a filling or lathe-cut?

A

machined from cast ingot (lump of melted metal)

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11
Q

What is characteristic of spherical method of particle making?

A

molten alloy blown through nozzle

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12
Q

How many sizes are typically observed from spherical method?

A

3

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13
Q

Is there a wide range of sizes from lathe-cute?

A

Yes

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14
Q

Why is there a wide range of sizes in lathe-cut?

A

optimum condensation

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15
Q

Do spherical particles that are wetted have a higher or lower mercury:alloy ratio than lathe-cut?

A

lower

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16
Q

At what percent is a product considered high-copper?

A

> 12

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17
Q

What is the advantage of high-copper products?

A

longevity and decreased creep

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18
Q

Is zinc-free alloy economically feasible?

A

No

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19
Q

Does zinc help or render machining lathe-cut particles?

A

it facilitates it and improves corrosion resistance

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20
Q

What are the benefits of heat treating alloy for dental amalgam?

A

eliminates non-uniformity, relieves stress, and lowers for the control of setting time

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21
Q

Is there free mercury found after the setting reaction?

A

No, only found in reaction phase

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22
Q

Is gamma 1 or 2 absent in set material?

A

2

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23
Q

What gamma is the major reaction phase in low and high-copper amalgams

A

gamma 1

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24
Q

What is characteristic in the first step of dental amalgam setting reaction?

A

form gamma 1 & 2

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25
Q

What is characteristic of the second step of dental amalgam setting reaction?

A

disappearance of gamma 2 phase and formation of nā€™ phase

26
Q

Is the setting reaction slower than for HCSS products than LCSS?

A

yes because of the two-step process

27
Q

At what time is the total dimensional change of dental amalgams limited by ADA standard no.1 ?

A

24 hours

28
Q

Can the dimensional changes be detected by the unaided eye?

A

No, the contractions cause microleaks

29
Q

What are the two different setting processes of dimensional changes?

A

solution and crystallization (precipitation)

30
Q

What is the strongest phase in dental amalgams?

A

incompletely consumed starting alloy particles (gamma)

31
Q

What is the weakest phase in dental amalgams?

A

gamma 2 in low-copper amalgams (most corrosion prone)

32
Q

What are the four main types of dental corrosion?

A

galvanic, electrochemical, crevice, and chemical

33
Q

Where does galvanic corrosion take place?

A

at interproximal contact with gold alloys

34
Q

Why does electrochemical corrosion take place?

A

bc multiple phases

35
Q

Where does crevice corrosion take place?

A

at the margins due to unpolished scratches, secondary anatomy, lower oxygen concentration = plaque retention

36
Q

Why does chemical corrosion occur?

A

reaction with sulfide ions at occlusal surface

37
Q

Is limited corrosion beneficial?

A

yes, because reduction in microleakage - gamma 2 in low copper amalgams and nā€™ in high-copper amalgams

38
Q

How is corrosion minimized?

A

polishing

39
Q

What element is clinically shown to have superior marginal integrity and longevity?

A

Zinc

40
Q

What are the two mechanical properties needed to resist forces of mastication?

A

comprehensive strength&raquo_space; tensile strength and proper dentinal support

41
Q

Describe poor edge strength

A

Fracture of ledge on poorly finished restoration

AKA low tensile strength leads to fracture in bending

42
Q

Would insufficient strength of amalgam leaf to and increased or decreased amount of marginal breakdown?

A

increased

43
Q

Which product has the most rapid setting reaction?

A

HCSS

44
Q

At what time period is the final strength of the amalgam identified?

A

1 week - nearly same strength as 1 days after

45
Q

Define viscoelastic materials

A

the mechanical properties depend on the rate of loading

46
Q

What is the avg compressive strength of amalgam after 24 hrs?

A

350Mpa or 50k psi

47
Q

What is the avg tensile strenght of amalgam after 24 hrs?

A

70 MPa or 10k psi

48
Q

Is a higher or lower ratio for compressive strength by tensile strength indicative of a brittle material?

A

high

49
Q

Do high-copper amalgam have high or low creep?

A

generally low

50
Q

True/False Creep is only a mechanical property.

A

True

it is correlated with clinical marginal fracture of low-copper amalgam

51
Q

What is the creep mechanism?

A

grain boundary sliding of gamma 1 phase

this is blocked by the nā€™ phase in high-copper amalgams

52
Q

What is the result of mercury content?

A

more phases, more expansion, less strength

53
Q

What is an affect of moisture and Zn-containing dental amalgam ?

A

delayed and excessive increase in setting expansion, decrease in strength

54
Q

What is the role of trituration ?

A

coat each alloy article with mercury

55
Q

What is the result in a small increase in trituration time?

A

decreases setting expansion and increase strength

56
Q

What is the result of a small increase in condensation pressure?

A

decrease setting expansion and increase in pressure

57
Q

True/False One should delay condensation after trituration.

A

False.

do NOT delay

58
Q

True/False The government threshold limit value for sustained exposure (40hr/wk) is 0.05 mg Hg/m3

A

True

59
Q

What is the ng of Hg per mL of blood that causes mercury poisoning?

A

100 ng per mL

60
Q

What are the mercury hygiene recommendations by ADA?

A

singly use, no touch, discard old/damaged, dispose in unbreakable jar holding water w/ finely divided sulfur

Dental Materials (6 decks)

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