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59 Cards in this Set

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component forming the main structure of the set material
base
component of the rxn that speeds up the setting rxn and is similar to the catalyst
accelerator
component that initates the setting rxn but does not become part of the final product
catalyst
lightly cross-linked material having elastic behavior after setting
elastomer
single-component material that is viscous enough to serve as a tray material yet serves as a syringe material after shear-thinning
monophase (single phase)
time-dependent pseudoplastic behavior of materials characterized by the gradual decrease of viscosity under a constant applied shear rate
thixotropic
time from start of mixing until just before elastic properties have developed
working time
time from start of mixing until material can resist permanent deformation
setting time
characteristic behavior of a material that behaves intermediate to an elastic solid (spring) and a viscous fluid (dashpot)
viscoelastic behavior
ADA spec 19 divides elastomeric impression materials into 3 types based on what?
selected elastic properties and dimsional change of the material
4 types of elastomers based on chemical composition
polysulfide, condensation silicone, addition silicone, polyether
definition of elastomeric impression materials
cross-linked polymeric two-paste materials that set by irreversible chemical reactions
elastomers are used to obtain highly accurate impressions for what type of restorations?
indirectly-fabricated
why do elastomers require tray adhesive?
to keep polymerization shrinkage in proper direction (toward tray)
what is the purpose of the fast strain rate (rapid removal) property of most elastomeric impression materials
reduces distortion and increases tear resistance
polysulfide setting rxn
[polymer + filler] + [lead dioxide] --> set material + H2O
function of lead dioxide in polysulfide setting rxn
brown reactor/accelerator paste; oxidizing agent
what does the base polymer contain in polysulfide?
linear polyfunctional mercaptan or polysulfide (characteristic odor)
lithopone or TiO2 filler
what is the plasticizer in polysulfide?
dibutyl phthalate
what are the retarders in polysulfide?
oleic/stearic acid retarders
what is cross-linked in the polysulfide setting rxn?
SH groups in the base polymer and lead dioxide
color of lead dioxide
brown
what type of reaction is the polysulfide setting rxn?
exothermic condensation polymerization rxn
vulcanization
formation of disulfide bonds (cross-linking)
nature of polymer in polysulfide
hydrophobic
speed of setting of polysulfide
slow setting: leave in mouth for 10 min
which material has the highest tear resistance of all impression materials?
polysulfide - so don't remove rapidly
which material has the slowest elastic strain recovery and most permanent deformation after compressive strain?
polysulfide
for polysulfide, how long should you wait to pour and why?
should be w/in 30 min but best if immediately to reduce shrinkage by water loss
which materials require custom tray?
polysulfide and polyether
which is the material that does not specify to use for edentulous ridges?
condensation silicone
what is added to the paste in silicone impression materials for condensation silicones?
reinforcing agents (silica)
setting rxn for condensation silicone
polymer + cross-linking agent --> set material + ethanol
what is the polymer for condensation silicone?
alpha - omega hydroxy-terminated polydimethyl siloxane
what does the polymer react with in condensation silicone?
tri or tetra functional alkyl silicates
cross-linking occurs bw what in condensation silicone?
silicone polymers and silicates
by product of condensation silicone
ethanol
what happens to the set condensation silicone material?
it will shrink and change dimension and release volatile by-product
compensation for polymerization shrinkage in condensation silicone products
putty-wash
amount of shrinkage for condensation silicone
.03-0.06%
when should you pour for condensation silicone rxns?
w/in 30 min, but after ethanol has evaporated
what are the implications of condensation silicone materials, since it is so very hydrophobic?
need dry field for impression and difficult to pour cast w/o getting bubbles in stone
does condensation silicone have high or low tear strength?
low
why is condensation silicone not used as commonly as addition silicones?
poor dimensional stability
setting reaction for addition silicone?
polymer + Pt salt w/ pre-polymer --> set material
what is the base of addition silicone?
polymethyl hydrogen siloxane
what is the catalyst for addition silicone?
divinyl polydimethyl siloxane
shrinkage on curing for addition silicone
0.05-0.16%
best dimensional stability
addition silicone
what do some manufacturers add to addition silicone to make it more hydrophilic?
surfactant
when do you pour the cast for addition silicone?
wait to permit the release of H2 gas
base for polyether
polyether pre-polymer, colloidal silica filler, glycolether or phthalate plasticizer
accelerator for polyether
sulfonate ester initiator, imine catalyst
which material has a high modulus of elasticity?
polyether
shrinkage on curing of polyether
0.15%
which material should you use on pts who gag?
polyether
does polyether have high or low tear strength?
low
least hydrophobic elastomer
polyether
where should you definitely not use polyether?
full arch impressions or for impression of sub-gingival region