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Operative Dentistry > Amalgam > Flashcards

Amalgam Flashcards

1
Q

describe the composition, setting reaction and influence of particle shape on traditional amalgam

A

70% silver
25% tin
3% copper
some zinc and some mercury

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2
Q

how does the behaviour of amalgam compare to composite resins

A
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3
Q

describe the mechanical properties of amalgam

A

strength
abrasion resistance
creep

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4
Q

describe the mechanical properties of copper enriched enamel

A

same as traditional but stronger due to presence of copper

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5
Q

describe the thermal properties of traditional enamel

A
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6
Q

describe the thermal properties of copper enriched amalgam

A
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7
Q

what are some factors affecting amalgams clinical performance

A
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8
Q

what is dental amalgam

A

an alloy formed from the reaction of liquid mercury and silver, tin, copper and other metal powders

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9
Q

why is particle shape of amalgam important to consider

A

it affects the handling properties like how easy it is to mix and apply as well as the final properties like its strength in restoration

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10
Q

what is the function of the silver and tin powder in amalgam

A

an intermetallic compound called Ag3Sn, reacts with mercury liquid to form amalgam in the gamma phase

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11
Q

what is the function of copper in the powder of amalgam

A

increase the strength and hardness of the material

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12
Q

what is the function of zinc in the powder of the amalgam

A

scavenger during production, preferentially oxidises and slag formed and removed. some zinc is free

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13
Q

what is the function of mercury powder in the amalgam

A

can allow it to react faster but only found in some traditional amalgams

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14
Q

what is the function of liquid mercury in amalgam

A

50% of amalgam by weight, is triple distilled and reacts with the metal powders to form amalgam

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15
Q

what are lathe cut particles

A

coarse, medium and fine particles formed by filing ingots

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16
Q

what are the spherical particle types

A

range of sizes and are formed by spraying molten metal into an inert atmosphere

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17
Q

what is the setting reaction of amalgam in simple terms

A

Ag3Sn + Hg -> Ag3Sn + Ag2Hg3 + Sn7Hg9

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18
Q

which section of the amalgam settings action is the amalgam matrix

A

Ag2Hg3 + Sn7Hg9

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19
Q

describe the gamma 1 phase

A

this is A2Hg3 ie silver mercury

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20
Q

describe gamma 2 phase

A

Sn7Hg9 ie tin mercury

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21
Q

what is the gamma phase

A

this is silver tin, and is found on both sides of the setting reaction as there are some unreacted particles left over

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22
Q

describe the set structure of amalgam

A

gamma gives good strength and corrosion resistance
gamma 1 gives good corrosion resistance
gamma 2 gives poor strength and low corrosion resistance

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23
Q

function of the voids in amalgam

A

decrease strength and increase corrosion

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24
Q

what is gamma in the amalgam structure

A

unreacted silver tin particles

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25
Q

which amalgam component has the greatest tensile strength

A

gamma silver tin at 170 MPa

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26
Q

what is the tensile strength of gamma 1

A

30 MPa

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27
Q

what is the tensile strength of gamma 2

A

20 MPa

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28
Q

what is the tensile strength of amalgam

A

60 MPa

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29
Q

what is responsible for initial contraction in setting the dimensional changes for traditional amalgam

A

a solution of alloy particles in mercury

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30
Q

describe the setting dimensional changes observed in traditional amalgam

A

solution of alloy particles in the mercury causes initial contraction, and then there is gamma 1 crystallisation to create expansion

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31
Q

describe the setting dimensional changes in modern amalgam

A

small contraction, with a solid solution of mercury in the gamma

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32
Q

is there any clinical sign of the dimensional changes caused by amalgam setting

A

no, as the expansion and contraction is less than 0.2% of the initial size

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33
Q

summarise zinc and expansion

A

this is about the interaction of zinc with saliva and blood, which leads to hydrogen bubbles forming the saliva, building pressure and causing expansion. if there is downward pressure than there is pulpal pain, and if there is upward pressure then the restoration will sit proud of the surface

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34
Q

why is it important to use zinc free materials

A

when zinc reacts with blood this creates hydrogen bubbles within the amalgam and expansion causing pulpal pain and raised restorations

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35
Q

what is the interaction of zinc with saliva and blood

A

Zn + H2O -> ZnO + H2

36
Q

what are the properties of amalgam dependent on

A

handling factors such as proportioning, titration, condensation, carving and polishing

cavity design

corrosion

some products have variations as well

37
Q

what are the advantages of spherical particles

A

less mercury required
higher tensile strength
higher early compressive strength
less sensitive to condensation
easier to carve

38
Q

what are the amalgam properties (long list)

A

strength
rigidity
abrasion resistance
creep
setting shrinkage
thermal expansion
thermal conductivity
corrosion
bond to tooth, microleakage
handling and viscosity
biocompatibility
aesthetics
radiopaque
anticariogenic
smooth surface

39
Q

describe the strength of amalgam

A

compressive strength to withstand biting forces
tensile forces as well for the abrasion resistance
early amalgam has a poor strength but over 24 hours sees an increase in strength

40
Q

describe the abrasion resistance seen in amalgam

A

high which is suitable for posterior teeth as teeth slide over one another during mastication

too high resistance for deciduous teeth

41
Q

what are factors that decrease the strength of amalgam

A

undermixing
too high mercury content after condensation
too low condensation pressure
slow rates of packing, meaning the increments do not bond
corrosion

42
Q

what does slow rate of packing mean for amalgam and why is it bad

A

this means you are not applying enough pressure when placing the material or you are taking too long to build up the material which leads to the increments not bonding properly

43
Q

describe creep in amalgam

A

amalgam is viso elastic. creep is when a material experiences low level stress levels ie below the elastic limit stress which are applied repeatedly over a prolonged period of time, resulting in flow and permanent deformation

creep affects the marginal integrity of amalgam, and also depends on cavity design and corrosion

44
Q

which materials experience creep the most

A

amalgam
alloys
waxes
plastics

45
Q

list the stages to amalgam creep

A

amalgam is fitted into the cavity
low magnitude forces are applied repeatedly through biting
amalgam shape sits proud around the margins
not long after, biting forces will break the edges off created divots around the margin

ultimately leads to micro leakage and potential for secondary caries

46
Q

how much can amalgam thermally expand

A

three times of the tooth

47
Q

describe the thermal conductivity of amalgam

A

high, may need to use liner or varnish in the deeper cavities

48
Q

describe the thermal conductivity of amalgam

A

high, so when a transient thermal stimuli is applied like through drinking tea, the amalgam temperature rises quite fast

49
Q

describe how amalgam bonds

A

it does not bond to the tooth and requires mechanical retention.
some suggest using new bonding systems base on 4-meta to get the bond to the tooth but this is not widely accepted

50
Q

describe corrosion of amalgam

A

gamma 2 is the most corrosive
the material weakens through corrosion at the margins particularly

51
Q

how can amalgam corrosion be reduced

A

copper enrichment
polishing margins
avoiding galvanic cells

52
Q

how are the amalgam aesthetics

A

poor

53
Q

is amalgam cariogenic

A

no

54
Q

what is the amalgam surface like

A

smooth if polished well, can deteriorate over time

55
Q

what are the two types of copper enriched amalgam

A

dispersion modified and single composition

56
Q

describe dispersion modified copper enriched amalgam

A

originally, silver-copper spheres and conventional lathe cut alloys were used.
originally it was thought that the spherical particles would act as a strengthening agent, but increased copper content gave beneficial modifications to setting reactions

57
Q

describe the process of the dispersion modified amalgam setting reaction

A

first, as a conventional material, gamma + Hg -> gamma, gamma1 and gamma2

second stages takes several days and is a reaction of gamma2 with silver copper to form Cu6Sn5 + gamma1

58
Q

describe the single composition formula of amalgam

A

powder is silver, tin and copper
12-30% copper
both spherical and lathe cut particles

59
Q

what is the setting reaction of single composition amalgam

A

Ag-Sn-Cu powder + Hg -> Ag-Sn-Cu + y1 _ Cu6Sn5

60
Q

describe what happens when Ag-Cu spheres were added to the normal lathe cut amalgam particles

A

a halo forms around the AgCu spheres. the halo consisted of Cu6Sn5. this is dispersion modified copper enriched amalgam with the halo acting as a fourth reaction product

61
Q

what was the first attempt to introduce copper to amalgam

A

addition of Ag-Cu spheres to lathe cut enamel particles which formed the halo as a fourth reaction product

62
Q

what was the second attempt to introduce copper to amalgam

A

have it within the amalgam powder itself, to eliminate the halo. this is the single composition form of copper enriched amalgam, with the setting reaction producing just three reaction products. better properties than the dispersion modified version

63
Q

what are the benefits of using copper enriched amalgam

A

higher early strength
less creep
higher corrosion resistance
increased durability of margins

64
Q

which amalgam has the most creep

A

traditional amalgam with lathe cut particles

65
Q

which amalgam has the lowest creep

A

copper enriched single composition amalgam

66
Q

what is permite

A

the amalgam material used in glasgow
non gamma 2 amalgam with lathe cut and spherical particles

67
Q

what is the compressive strength of permite after 24 hours

A

goes from 260MPa to 500 MPa

68
Q

enamel compressive strength

A

250MPa

69
Q

dentine compressive strength

A

280MPa

70
Q

hybrid composite compressive strength

A

300 MPa

71
Q

amalgam compressive strength

A

500MPa

72
Q

enamel tensile strength

A

35

73
Q

dentine tensile strength

A

40-260

74
Q

hybrid composite tensile strength

A

50

75
Q

amalgam tensile strength

A

60

76
Q

elastic modulus units

A

GPa

77
Q

elastic modulus of enamel

A

50

78
Q

elastic modulus of dentine

A

12

79
Q

elastic modulus of hybrid composite

A

14

80
Q

elastic modulus of amalgam

A

30

81
Q

hardness of enamel

A

350

82
Q

hardness of dentine

A

60

83
Q

hardness of hybrid composite

A

90

84
Q

hardness of amalgam

A

100

85
Q

advantages of amalgam

A

strong
hard
durable
radiopaque
user friendly

86
Q

disadvantages of amalgam

A

corrosion
leakage
does not bond to tooth
poor aesthetics
mercury has a perceived toxicity and environmental impact should also be considered

87
Q

how is amalgam classified

A

according to particle shape and size, and traditional vs non gamma 2

Operative Dentistry (22 decks)

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