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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
which amalgam component has the greatest tensile strength
gamma silver tin at 170 MPa
26
what is the tensile strength of gamma 1
30 MPa
27
what is the tensile strength of gamma 2
20 MPa
28
what is the tensile strength of amalgam
60 MPa
29
what is responsible for initial contraction in setting the dimensional changes for traditional amalgam
a solution of alloy particles in mercury
30
describe the setting dimensional changes observed in traditional amalgam
solution of alloy particles in the mercury causes initial contraction, and then there is gamma 1 crystallisation to create expansion
31
describe the setting dimensional changes in modern amalgam
small contraction, with a solid solution of mercury in the gamma
32
is there any clinical sign of the dimensional changes caused by amalgam setting
no, as the expansion and contraction is less than 0.2% of the initial size
33
summarise zinc and expansion
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
34
why is it important to use zinc free materials
when zinc reacts with blood this creates hydrogen bubbles within the amalgam and expansion causing pulpal pain and raised restorations
35
what is the interaction of zinc with saliva and blood
Zn + H2O -> ZnO + H2
36
what are the properties of amalgam dependent on
handling factors such as proportioning, titration, condensation, carving and polishing cavity design corrosion some products have variations as well
37
what are the advantages of spherical particles
less mercury required higher tensile strength higher early compressive strength less sensitive to condensation easier to carve
38
what are the amalgam properties (long list)
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
describe the strength of amalgam
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
describe the abrasion resistance seen in amalgam
high which is suitable for posterior teeth as teeth slide over one another during mastication too high resistance for deciduous teeth
41
what are factors that decrease the strength of amalgam
undermixing too high mercury content after condensation too low condensation pressure slow rates of packing, meaning the increments do not bond corrosion
42
what does slow rate of packing mean for amalgam and why is it bad
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
describe creep in amalgam
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
which materials experience creep the most
amalgam alloys waxes plastics
45
list the stages to amalgam creep
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
how much can amalgam thermally expand
three times of the tooth
47
describe the thermal conductivity of amalgam
high, may need to use liner or varnish in the deeper cavities
48
describe the thermal conductivity of amalgam
high, so when a transient thermal stimuli is applied like through drinking tea, the amalgam temperature rises quite fast
49
describe how amalgam bonds
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
describe corrosion of amalgam
gamma 2 is the most corrosive the material weakens through corrosion at the margins particularly
51
how can amalgam corrosion be reduced
copper enrichment polishing margins avoiding galvanic cells
52
how are the amalgam aesthetics
poor
53
is amalgam cariogenic
no
54
what is the amalgam surface like
smooth if polished well, can deteriorate over time
55
what are the two types of copper enriched amalgam
dispersion modified and single composition
56
describe dispersion modified copper enriched amalgam
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
describe the process of the dispersion modified amalgam setting reaction
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
describe the single composition formula of amalgam
powder is silver, tin and copper 12-30% copper both spherical and lathe cut particles
59
what is the setting reaction of single composition amalgam
Ag-Sn-Cu powder + Hg -> Ag-Sn-Cu + y1 _ Cu6Sn5
60
describe what happens when Ag-Cu spheres were added to the normal lathe cut amalgam particles
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
what was the first attempt to introduce copper to amalgam
addition of Ag-Cu spheres to lathe cut enamel particles which formed the halo as a fourth reaction product
62
what was the second attempt to introduce copper to amalgam
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
what are the benefits of using copper enriched amalgam
higher early strength less creep higher corrosion resistance increased durability of margins
64
which amalgam has the most creep
traditional amalgam with lathe cut particles
65
which amalgam has the lowest creep
copper enriched single composition amalgam
66
what is permite
the amalgam material used in glasgow non gamma 2 amalgam with lathe cut and spherical particles
67
what is the compressive strength of permite after 24 hours
goes from 260MPa to 500 MPa
68
enamel compressive strength
250MPa
69
dentine compressive strength
280MPa
70
hybrid composite compressive strength
300 MPa
71
amalgam compressive strength
500MPa
72
enamel tensile strength
35
73
dentine tensile strength
40-260
74
hybrid composite tensile strength
50
75
amalgam tensile strength
60
76
elastic modulus units
GPa
77
elastic modulus of enamel
50
78
elastic modulus of dentine
12
79
elastic modulus of hybrid composite
14
80
elastic modulus of amalgam
30
81
hardness of enamel
350
82
hardness of dentine
60
83
hardness of hybrid composite
90
84
hardness of amalgam
100
85
advantages of amalgam
strong hard durable radiopaque user friendly
86
disadvantages of amalgam
corrosion leakage does not bond to tooth poor aesthetics mercury has a perceived toxicity and environmental impact should also be considered
87
how is amalgam classified
according to particle shape and size, and traditional vs non gamma 2

Operative Dentistry (22 decks)

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