Elastomers Flashcards
what are the 2 types of elastomer
polyether
addition silicones
how are elastomers formed
polymerisation with cross linking polymer chains
what does cross linking cause
generation of elastic properties
fluid to solid transition
what do the byproducts of polymerisation affect
dimensional stability and cast compatibility
how do you assess the material properties of an elastomer
surface detail
flow/viscosity
contact angle
elastic recovery
stiffness
tear strength
mixing time
working time
shore A hardness
shark fin test
setting shrinkage
dimensional stability
thermal expansion coefficient
biocompatability
what are the ideal properties of an impression material
quality of surface interaction between material and tooth/soft tissues
accuracy
dealing with removal and undercuts
dimensional stability
what should viscosity of elastomers be
able to flow readily
what should surface wetting be
make intimate contact
what is a contact angle
determines how well material envelopes the hard/soft tissue surface
what is viscosity
ability of materials ability to flow and how well it records surface detial
what does a large contact angle result in
spaces between globules of impression material so some of tooth surface not replicated
what type of contact angle do we want
small contact angle
what do hydrophilic silicones do
wet tooth surface
what are the standard notch dimensions for reproduction of surface detail
20um
50um
75um
what is visco elastic recovery
impression material will have some permanent strain once load is removed
