Elastomeric Impression materials Flashcards
what are the problems with hydrocolloid materials?
poor tear resistance
poor dimensional stability
what are the 4 types of elastomeric impression materials?
polysulphides
silicone rubbers - condensation curing/addition curing
polyether
what is the committee that classifies impression materials by chemical nature and consistency?
ISO 4823
what does consistency dictate?
clinical application
putty has more inert fillers which make it?
more dimensionally accurate = does not flow very well because of viscosity = does not capture fine detail
clinical properties of putty?
high dimensional stability
tissue displacing
poor fine detail capture
properties of light bodied materials?
low dimensional stability
limited tissue displacement
fine detail capture
combine viscosities to maximise?
clinical application
polysulphides come as?
2 pastes
what is the polysulphides baste paste?
baste paste is white terminal and pendant thiol SH groups - bad smell -polysulphide prepolymer -plasticiser -inert filler
what is in the catalyst paste on polysulphides?
dark brown
lead dioxide
sulphur
inert oil
how do polysulphides set?
by condensation polymerisation
as cross linking occurs in polysulphides what happens?
increased viscosity and elasticity
after mixing, what happens to polysulphides?
gradual increase in viscosity
slow development of elasticity
set time is 10 mins
polysulphides have a high what? and slow?
high tear resistance
slow incomplete elastic recovery
what have the best dimensional stability?
heavily bodied materials
reactions of polysulphides continue with?
water loss
concerns of use of what constituent in polysulphides?
lead
polysulphide has a bad?
odour and taste
are polysulphide impressions easy to read?
yes
condensation cured silicone rubbers come as?
2 pastes or a paste and a liquid
what types of condensation cured silicone rubbers can you get?
putty, heavy/regular/light bodied
what is the setting reaction of condensation cured silicone rubber?
cross linking of hydroxyl terminated polydimethylsiloxane chains
what is the catalyst in condensation cured silicone rubbers setting reaction? what is the cross linking agent?
catalyst - tin compound
cross linking agent - alkyl silicate
what is a by product of condensation cured silicone rubbers setting reaction? what can it cause?
C2H5OH - an alcohol
can potentially make it dimensionally unstable
what does cross linking in the condensation cure setting reaction cause?
increases materials viscosity and elastic properties
paste one of silicone rubber (condensation) is?
hydroxyl terminated polydimethylsiloxane chains - liquid silicone prepolymer
inert fillers - e.g silica
paste 2 of silicone rubber (condensation) is?
alkyl silicate
tin compound e.g dibutly tin dilaurate
silicone rubber (C) set time is?
less than polysulphides
silicone rubber (C)’s elasticity develops?
more rapidly than polysulphides
is silicone rubber (C) hydrophobic or hydrophillic?
hydrophobic
what is the wear resistance of silicone rubber C like?
elastic recovery is?
adequate
good elastic recovery
silicone rubbers C have post setting dimensional changes so must pour soon, with loss of?
loss of volatile by product
silicone rubber addition curing paste 1?
filler
liquid silicone prepolymer - white
some methyl groups replaced with vinyl groups
catalyst e.g chlorplatinic acid
paste 2 of silicone rubber addition curing?
filler
liquid silicone prepolymer
polydmethylsiloxane prepolymer with some methyl groups replaced with hydrogen
silicone rubber addition cured is available in what forms?
automax form
viscosities of - putty, regular and light
what is the setting reaction of addition cured silicone rubber?
platinum catalysed addition reaction
no by products
hydrogen gas possibly involved b/c platinum catalyst with moisture
properties of silicone rubber addition cured?
as for condensation silicones
no by products
hydrophobic - but some new formulas have surface active agents to make it more hydrophillic
polyether - 2 pastes. what is the base paste?
comes in large tube
imine terminated polymer
inert filler
polyether catalyst?
smaller tube
reaction initiator - aromatic sulphonic acid ester
paste forming oils and fillers
polyether also available in what units?
automix
how do polyethers set?
by cationic ring opening addition polymerisation
no by products
as setting of polyethers increases what happens?
viscosity increases = rigid cross linked rubber
polyethers have similar tear reistance and elastic properites to?
silicones
polyethers rigidity makes it?
hard to remove
difficult to remove die without fracture
good for implant work
use limited because polyethers do not come as?
heavy bodied or puttys
are polyethers hydrophobic or hydrophillic?
hydrophillic
what can polyethers cause?
an allergy
limit emersion of polyethers to?
10 mins in hypochlorite
