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BDS2 CDS DMS > amalgam > Flashcards

amalgam Flashcards

1
Q

what is dental amalgam?

A

an alloy formed by the reaction of mercury(l) and silver/tin/copper/other metal powder

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2
Q

what are the 2 classifications of amalgam?

A

traditional

copper enriched

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3
Q

what are the functions of silver/tin

A

gamma phase

reacts with Hg liquid to form amalgam

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4
Q

what is the function of copper?

A

increases strength and hardness

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5
Q

what is the function of zinc

A

scavenger during production
preferentially oxidises and slag formed/removed
-some zinc free

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6
Q

what is the function of Hg in powder?

A

pre-amalgamated alloys react faster

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7
Q

describe lathe cut particles

A

coarse, medium, fine

formed by filing ingots

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8
Q

describe spherical particles?

A

range of particle sizes

formed by spraying molten metal into inert atmosphere

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9
Q

what is the simplified setting reaction?

A

powder + liquid -> unreacted particles + amalgam matrix

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10
Q

describe gamma particles

A

good strength & corrosion resistance

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11
Q

describe gamma 1

A

good corrosion resistance

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12
Q

describe gamma 2

A

weak poor corrosion resistance

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13
Q

which gamma has the highest tensile strength?

A

gamma

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14
Q

what are the setting dimensional changes in traditional amalgam?

A

initial contraction -solution of alloy particles in Hg

expansion - gamma 1 crystalisation

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15
Q

what are the setting dimensional changes in modern amalgam?

A

small contraction

solid solution of Hg in Ag3Sn

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16
Q

why does zinc cause expansion?

A

bubbles of H2 formed within amalgam
pressure build up causes expansion
downward pressure can cause pulpal pain
upward- rest sits proud

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17
Q

what affects amalgam properties?

A 
handling factors
-proportioning & trituration
-condensation
-carving & polishing
dependent on cavity design
affected by corrosion
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18
Q

what are the advantages of spherical particles?

A 
less Hg required
higher tensile strength
higher early compressive strength
less sensitive to condensation
easier to carve
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19
Q

describe the strength of amalgam

A

early poor

late (>24hrs) ok

20
Q

what factors decrease strength?

A 
undermixing
too high Hg content after condensation
too low condensation pressure
slow rate of packing
-increments dont bond
corrosion
21
Q

describe creep in amalgam

A

visco-elastic
-results in deformation
high in traditional
affects marginal integrity

22
Q

what is creep?

A

when a material experiences low-level stress levels which are applied repeatedly
over prolonged time it may flow-permanent deformation

23
Q

what materials does creep affect?

A

amalgam
alloys
waxes
plastics

24
Q

what happens when amalgam experiences creep?

A 
sits proud of tooth
causes ditched margins
vulnerable to fracture at margins
causes microleakage
leads to secondary caries
25
Q

what is the biocompatibility concern in amalgam?

A

mercury toxicity

26
Q

what is the thermal expansion?

A

x3 of tooth

27
Q

what is the thermal conductivity?

A

high

may need to use liner/varnish in deep cavities

28
Q

what is the thermal diffusivity?

A

high

when transient thermal stimuli applied amalgams temp rises quickly

29
Q

describe amalgam bonding

A

doesnt bond to tooth

needs mechanical retention

30
Q

describe the handling/viscosity

A

mixing, working, setting times ok
viscosity
-packing into cavity= user friendly

31
Q

describe corrosion

A 
gamma 2 most electronegative
weakens material at margins
may contribute to sealing margins
reduced by:
-copper enriched
-polishing margins
-avoiding galvanic cells
32
Q

aesthetics?

A

poor

33
Q

radiopaque?

A

yes

34
Q

anticariogenic?

A

no

35
Q

smooth surface?

A

yes, if well polished, may deteriorate

36
Q

setting shrinkage?

A

net overall shrinkage

37
Q

what are the 2 types of copper enriched amalgam?

A

dispersion modified
single composition types
-introduced to increase uptake by profession
-more common

38
Q

what is dispersion modified amalgam?

A

Ag-Cu spheres + conventional lathe cut alloy

39
Q

what is the benefit of copper?

A

modification to setting reaction

40
Q

what are the benefits of copper enriched?

A

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

41
Q

what is the thermal expansion rate the same as?

A

enamel and dentine

42
Q

what is the failure rate lower than?

A

all composites

43
Q

what are the advantages of amalgam?

A 
strong
hard
durable
radiopaque
user friendly
44
Q

what are the disadvantages of amalgam?

A 
corrosion
leakage
poor aesthetics
mercury
-perceived toxicity
-environmental impact
45
Q

which type of amalgam has the least microleakage?

A

permite

BDS2 CDS DMS (16 decks)

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