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Elastomeric impression materials Flashcards

1
Q

4 types of elastomeric impression material

A
  • polysulphides
  • silicone rubbers (condensation curing)
  • silicon (addition curing)
  • polyether
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2
Q

ISO 4823 classifies elastomeric impression materials according to what? 2

A

chemical nature

consistency (viscosity)

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3
Q

type 0 elastomeric impression materials consistency and like?

A

very high viscosity
putty

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4
Q

type 1 elastomeric impression materials consistency and like?

A

high viscosity
heavy bodied

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5
Q

type 2 elastomeric impression materials consistency and like?

A

medium viscosity
medium bodied

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6
Q

type 3 elastomeric impression materials consistency and like?

A

low viscosity
light bodied

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7
Q

do putty elastomeric impression materials capture fine details? why? 2

A

no
high dimensional stability
tissue displacing

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8
Q

do light bodied elastomeric impression materials capture fine details? why?

A

yes
low dimensional stability
limited tissue displacement

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9
Q

polysulphides consist of what? 2

A

base paste - white
catalyst paste - dark brown

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10
Q

what does the base paste of polysulphides contain? 4

A
  • terminal and pendant thiol groups for cross linking
  • polysulphide prepolymer
  • plasticiser
  • inert filler
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11
Q

what does the catalyst paste of polysulphides contain? 3

A
  • PbO2
  • sulphur
  • inert oil
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12
Q

what type of setting reaction is polysulphides?

A

condensation polymerisation

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13
Q

positives of polysulphides 4

A
  • high tear resistance
  • heavy bodied so best dimensional stability
  • reaction continues with water loss
  • impression easily read
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14
Q

negatives of polysulphides 3

A
  • slow incomplete elastic recovery
  • concerns over use of lead
  • bad odour and taste
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15
Q

silicone rubbers (condensation curing) are 2 pastes consisting of what? 4

A
  • hydroxyl terminated polydimethylsiloxane chains
  • inert fillers
  • alkyl silicate
  • tin compound
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16
Q

what is the function of hydroxyl polydimethylsiloxane chains in the setting reaction of silicone rubbers (condensation curing)?

A

cross linkage of chains increases viscosity and elastic properties

17
Q

what is the function of alkyl silicate in the setting reaction of silicone rubbers (condensation curing)?

A

cross linking agent

18
Q

what is the function of tin compound in the setting reaction of silicone rubbers (condensation curing)?

19
Q

compare the set time of silicone rubbers (condensation curing) to polysulphides

A

set time of silicone rubbers (condensation curing) is less than polysulphides

20
Q

compare the elasticity of silicone rubbers (condensation curing) to polysulphides

A

elasticity of silicone rubbers (condensation curing) develops more rapidly than polysulphides

21
Q

compare the tear resistance of silicone rubbers (condensation curing) to polysulphides

A

tear resistance of silicone rubbers (condensation curing) is adequate but not as good as polysulphides

22
Q

are silicone rubbers (condensation curing) hydrophilic or hydrophobic?

A

hydrophobic

23
Q

what is the elastic recovery of silicone rubbers (condensation curing)?

A

good elastic recovery

24
Q

silicone rubbers (addition reaction) is catalysed by what?

25
Q

explain the setting reaction of silicone rubber (addition reaction)

A

in one paste the methyl group CH3 is replaced by a hydrogen
in the other past the methyl CH3 is replaced by a vinyl group CH2=CH
platinum catalyst connects the vinyl and hydrogen group forming - CH2 - CH2 -

26
Q

polyethers are made of what 2 pastes

A

base paste
a catalyst paste

27
Q

the base paste of polyethers is composed of? 2

A

imine terminate prepolymer

inert filler

28
Q

the catalyst paste of polyethers is composed of? 2

A

a catalyst of aromatic Sulphonic acid ester

paste forming oils and fillers

29
Q

what type of reaction is the setting reaction of polyethers?

A

cationic ring opening addition polymerisation

30
Q

what are the steps of the setting reaction of polyethers? 4

A

activation - aromatic sulphonic acid ester becomes ionised

initiation - reacts with prepolymer

propagation - process repeated so more chains form

termination - all reactants are consumed

31
Q

compare the tear resistance and elastic properties of polyethers to silicones

32
Q

what limits the use of polyethers?

A

lack of heavy body / putty

33
Q

are polyethers hydrophilic or hydrophobic?

A

hydrophobic - issue in humid environments

34
Q

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2 Dental Materials (4 decks)

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