elastomeric impression materials Flashcards
what are main problems re. hydrocolloid materials?
poor tear resistance
poor dimensional stabilty
what are the 4 types of elastomeric impression materials?
polysulphides
silicone rubber (condensation curing)
silicone rubber (addition curing)
polyether
what material is preffered re implant work?
polether
how are elastomeric materials classified?
according to chemical nature
according to consistency
type 0?
very high consistency- putty
type 1? h
high consistency- heavy body
type 2?
medium consistency- medium bodied
type 3?
low consistency- light body
properties of putty?
high dimensional stability
tissue displacement
poor fine detail capture
properties of light body?
low dimensional stability
limited tissue displacement
fine detail capture
what are benefits of polysuphides?
very easy to read
disadvantages of polysulphides?
unpleasant for patient re. smell and taste
what is base paste of polysuphides?
terminal and pendant thiol -SH groups
polysulphide prepolymer
plasticiser ( di-n-butyl phthalate)
inert filler (chalk/Ti)2)
what is the catylst paste of polysulphides?
pbo2 ( lead dioxide)
sulphur
inert oil
what is the setting re. polysulphides?
condensation polymerisation
as cross linking occurs what increase?
viscosity and elastcity
what is setting reaction re silicone rubbers- condensation curing
cross linkin of hydroxyl terminated polydimethylsiloxane chains
what is the by product of the setting reaction of silicone rubbers- condensation curing?
ethyl alcohol
what is the cross linking agent re. condensation curing silicone rubber>
alkyl silicate
what is the catalyst re. condensation curing silicone rubber?
tin compound
what is the compostion of silicone rubbers - condensation curing?
paste- hydroxyl terminated polydimethylsilxane chains+ inert fillers (silica)
paste 2/liquid- alkyl silicate+ tin compound
what are the properties of silicone rubber- condensation curing?
set times less than polysulphides elasticity develops more rapidly tear resistance adequate good elastic recovery post setting dimensional changes
what are the by products re. addition curing and silicone rubber?
none
? hydrogen gas
what is the setting reaction re addition curing and silicone rubbers?
platinum catalysed addition reaction
what are the two pastes re. polyether?
base paste- imine terminated prepolymer+ inert filler
catalyst- aromatic suphonic acid ester+ oils and fillers
what is the setting reaction re. polyether?
by catatonic ring opening addition polymerisation
no by products
what are the stages of setting re polyether?
activation
initiation
propagation
termination
what are properties re. polyethers?
good tear resistance and elastic properties relatively rigid lacks of heavy body limits use hydrophilic must limit immersion in hypochlorite
