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Dental Materials > Elastomeric Impression materials > Flashcards

Elastomeric Impression materials Flashcards

1
Q

what are the problems with hydrocolloid materials?

A

poor tear resistance

poor dimensional stability

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2
Q

what are the 4 types of elastomeric impression materials?

A

polysulphides
silicone rubbers - condensation curing/addition curing
polyether

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3
Q

what is the committee that classifies impression materials by chemical nature and consistency?

A

ISO 4823

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4
Q

what does consistency dictate?

A

clinical application

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5
Q

putty has more inert fillers which make it?

A

more dimensionally accurate = does not flow very well because of viscosity = does not capture fine detail

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6
Q

clinical properties of putty?

A

high dimensional stability
tissue displacing
poor fine detail capture

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7
Q

properties of light bodied materials?

A

low dimensional stability
limited tissue displacement
fine detail capture

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8
Q

combine viscosities to maximise?

A

clinical application

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9
Q

polysulphides come as?

A

2 pastes

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10
Q

what is the polysulphides baste paste?

A 
baste paste is white
terminal and pendant thiol SH groups - bad smell
-polysulphide prepolymer
-plasticiser
-inert filler
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11
Q

what is in the catalyst paste on polysulphides?

A

dark brown
lead dioxide
sulphur
inert oil

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12
Q

how do polysulphides set?

A

by condensation polymerisation

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13
Q

as cross linking occurs in polysulphides what happens?

A

increased viscosity and elasticity

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14
Q

after mixing, what happens to polysulphides?

A

gradual increase in viscosity
slow development of elasticity
set time is 10 mins

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15
Q

polysulphides have a high what? and slow?

A

high tear resistance

slow incomplete elastic recovery

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16
Q

what have the best dimensional stability?

A

heavily bodied materials

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17
Q

reactions of polysulphides continue with?

A

water loss

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18
Q

concerns of use of what constituent in polysulphides?

A

lead

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19
Q

polysulphide has a bad?

A

odour and taste

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20
Q

are polysulphide impressions easy to read?

A

yes

21
Q

condensation cured silicone rubbers come as?

A

2 pastes or a paste and a liquid

22
Q

what types of condensation cured silicone rubbers can you get?

A

putty, heavy/regular/light bodied

23
Q

what is the setting reaction of condensation cured silicone rubber?

A

cross linking of hydroxyl terminated polydimethylsiloxane chains

24
Q

what is the catalyst in condensation cured silicone rubbers setting reaction? what is the cross linking agent?

A

catalyst - tin compound

cross linking agent - alkyl silicate

25
Q

what is a by product of condensation cured silicone rubbers setting reaction? what can it cause?

A

C2H5OH - an alcohol

can potentially make it dimensionally unstable

26
Q

what does cross linking in the condensation cure setting reaction cause?

A

increases materials viscosity and elastic properties

27
Q

paste one of silicone rubber (condensation) is?

A

hydroxyl terminated polydimethylsiloxane chains - liquid silicone prepolymer
inert fillers - e.g silica

28
Q

paste 2 of silicone rubber (condensation) is?

A

alkyl silicate

tin compound e.g dibutly tin dilaurate

29
Q

silicone rubber (C) set time is?

A

less than polysulphides

30
Q

silicone rubber (C)’s elasticity develops?

A

more rapidly than polysulphides

31
Q

is silicone rubber (C) hydrophobic or hydrophillic?

A

hydrophobic

32
Q

what is the wear resistance of silicone rubber C like?

elastic recovery is?

A

adequate

good elastic recovery

33
Q

silicone rubbers C have post setting dimensional changes so must pour soon, with loss of?

A

loss of volatile by product

34
Q

silicone rubber addition curing paste 1?

A

filler
liquid silicone prepolymer - white
some methyl groups replaced with vinyl groups
catalyst e.g chlorplatinic acid

35
Q

paste 2 of silicone rubber addition curing?

A

filler
liquid silicone prepolymer
polydmethylsiloxane prepolymer with some methyl groups replaced with hydrogen

36
Q

silicone rubber addition cured is available in what forms?

A

automax form

viscosities of - putty, regular and light

37
Q

what is the setting reaction of addition cured silicone rubber?

A

platinum catalysed addition reaction
no by products
hydrogen gas possibly involved b/c platinum catalyst with moisture

38
Q

properties of silicone rubber addition cured?

A

as for condensation silicones
no by products
hydrophobic - but some new formulas have surface active agents to make it more hydrophillic

39
Q

polyether - 2 pastes. what is the base paste?

A

comes in large tube
imine terminated polymer
inert filler

40
Q

polyether catalyst?

A

smaller tube
reaction initiator - aromatic sulphonic acid ester
paste forming oils and fillers

41
Q

polyether also available in what units?

A

automix

42
Q

how do polyethers set?

A

by cationic ring opening addition polymerisation

no by products

43
Q

as setting of polyethers increases what happens?

A

viscosity increases = rigid cross linked rubber

44
Q

polyethers have similar tear reistance and elastic properites to?

A

silicones

45
Q

polyethers rigidity makes it?

A

hard to remove
difficult to remove die without fracture
good for implant work

46
Q

use limited because polyethers do not come as?

A

heavy bodied or puttys

47
Q

are polyethers hydrophobic or hydrophillic?

A

hydrophillic

48
Q

what can polyethers cause?

A

an allergy

49
Q

limit emersion of polyethers to?

A

10 mins in hypochlorite

Dental Materials (13 decks)

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