elastomeric impression materials

Question 1

what are main problems re. hydrocolloid materials?

Answer 1

poor tear resistance

poor dimensional stabilty

Question 2

what are the 4 types of elastomeric impression materials?

Answer 2

polysulphides
silicone rubber (condensation curing)
silicone rubber (addition curing)
polyether

Question 3

what material is preffered re implant work?

Answer 3

polether

Question 4

how are elastomeric materials classified?

Answer 4

according to chemical nature

according to consistency

Question 5

type 0?

Answer 5

very high consistency- putty

Question 6

type 1? h

Answer 6

high consistency- heavy body

Question 7

type 2?

Answer 7

medium consistency- medium bodied

Question 8

type 3?

Answer 8

low consistency- light body

Question 9

properties of putty?

Answer 9

high dimensional stability
tissue displacement
poor fine detail capture

Question 10

properties of light body?

Answer 10

low dimensional stability
limited tissue displacement
fine detail capture

Question 11

what are benefits of polysuphides?

Answer 11

very easy to read

Question 12

disadvantages of polysulphides?

Answer 12

unpleasant for patient re. smell and taste

Question 13

what is base paste of polysuphides?

Answer 13

terminal and pendant thiol -SH groups
polysulphide prepolymer
plasticiser ( di-n-butyl phthalate)
inert filler (chalk/Ti)2)

Question 14

what is the catylst paste of polysulphides?

Answer 14

pbo2 ( lead dioxide)
sulphur
inert oil

Question 15

what is the setting re. polysulphides?

Answer 15

condensation polymerisation

Question 16

as cross linking occurs what increase?

Answer 16

viscosity and elastcity

Question 17

what is setting reaction re silicone rubbers- condensation curing

Answer 17

cross linkin of hydroxyl terminated polydimethylsiloxane chains

Question 18

what is the by product of the setting reaction of silicone rubbers- condensation curing?

Answer 18

ethyl alcohol

Question 19

what is the cross linking agent re. condensation curing silicone rubber>

Answer 19

alkyl silicate

Question 20

what is the catalyst re. condensation curing silicone rubber?

Answer 20

tin compound

Question 21

what is the compostion of silicone rubbers - condensation curing?

Answer 21

paste- hydroxyl terminated polydimethylsilxane chains+ inert fillers (silica)
paste 2/liquid- alkyl silicate+ tin compound

Question 22

what are the properties of silicone rubber- condensation curing?

Answer 22

set times less than polysulphides
elasticity develops more rapidly
tear resistance adequate
good elastic recovery
post setting dimensional changes

Question 23

what are the by products re. addition curing and silicone rubber?

Answer 23

none

? hydrogen gas

Question 24

what is the setting reaction re addition curing and silicone rubbers?

Answer 24

platinum catalysed addition reaction

Question 25

what are the two pastes re. polyether?

Answer 25

base paste- imine terminated prepolymer+ inert filler

catalyst- aromatic suphonic acid ester+ oils and fillers

Question 26

what is the setting reaction re. polyether?

Answer 26

by catatonic ring opening addition polymerisation

no by products

Question 27

what are the stages of setting re polyether?

Answer 27

activation
initiation
propagation
termination

Question 28

what are properties re. polyethers?

Answer 28

good tear resistance and elastic properties
relatively rigid
lacks of heavy body limits use
hydrophilic
must limit immersion in hypochlorite