Elastomeric impression materials

Question 1

4 types of elastomeric impression material

Answer 1

• polysulphides
• silicone rubbers (condensation curing)
• silicon (addition curing)
• polyether

Question 2

ISO 4823 classifies elastomeric impression materials according to what? 2

Answer 2

chemical nature

consistency (viscosity)

Question 3

type 0 elastomeric impression materials consistency and like?

Answer 3

very high viscosity
putty

Question 4

type 1 elastomeric impression materials consistency and like?

Answer 4

high viscosity
heavy bodied

Question 5

type 2 elastomeric impression materials consistency and like?

Answer 5

medium viscosity
medium bodied

Question 6

type 3 elastomeric impression materials consistency and like?

Answer 6

low viscosity
light bodied

Question 7

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

Answer 7

no
high dimensional stability
tissue displacing

Question 8

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

Answer 8

yes
low dimensional stability
limited tissue displacement

Question 9

polysulphides consist of what? 2

Answer 9

base paste - white
catalyst paste - dark brown

Question 10

what does the base paste of polysulphides contain? 4

Answer 10

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

Question 11

what does the catalyst paste of polysulphides contain? 3

Answer 11

• PbO2
• sulphur
• inert oil

Question 12

what type of setting reaction is polysulphides?

Answer 12

condensation polymerisation

Question 13

positives of polysulphides 4

Answer 13

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

Question 14

negatives of polysulphides 3

Answer 14

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

Question 15

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

Answer 15

• hydroxyl terminated polydimethylsiloxane chains
• inert fillers
• alkyl silicate
• tin compound

Question 16

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

Answer 16

cross linkage of chains increases viscosity and elastic properties

Question 17

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

Answer 17

cross linking agent

Question 18

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

Answer 18

catalyst

Question 19

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

Answer 19

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

Question 20

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

Answer 20

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

Question 21

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

Answer 21

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

Question 22

are silicone rubbers (condensation curing) hydrophilic or hydrophobic?

Answer 22

hydrophobic

Question 23

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

Answer 23

good elastic recovery

Question 24

silicone rubbers (addition reaction) is catalysed by what?

Answer 24

platinum

Question 25

explain the setting reaction of silicone rubber (addition reaction)

Answer 25

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 -

Question 26

polyethers are made of what 2 pastes

Answer 26

base paste a catalyst paste

Question 27

the base paste of polyethers is composed of? 2

Answer 27

imine terminate prepolymer inert filler

Question 28

the catalyst paste of polyethers is composed of? 2

Answer 28

a catalyst of aromatic Sulphonic acid ester paste forming oils and fillers

Question 29

what type of reaction is the setting reaction of polyethers?

Answer 29

cationic ring opening addition polymerisation

Question 30

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

Answer 30

activation - aromatic sulphonic acid ester becomes ionised initiation - reacts with prepolymer propagation - process repeated so more chains form termination - all reactants are consumed

Question 31

compare the tear resistance and elastic properties of polyethers to silicones

Answer 31

similar

Question 32

what limits the use of polyethers?

Answer 32

lack of heavy body / putty

Question 33

are polyethers hydrophilic or hydrophobic?

Answer 33

hydrophobic - issue in humid environments

Question 34

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