impression materials Flashcards
does an impression produce a positive or negative reproduction of tissues?
negative
which material is used to fill an impression and produce a positive replica?
dental stone
name the 2 clinical classifications of impression materials?
mucostatic
mucocompressive
which type of impression material will displace the soft tissues slightly to give an impression of the undisplayed mucosa?
mucostatic
which type of impression material is a viscous material that records an impression of the mucosa underpaid?
mucocompressive
are low viscosity alginates mucostatic or mucocompressive?
mucostatic
are high viscosity alginates mucostatic or mucocompressive?
mucocompressive
no impression material is truly elastic, they are instead?
viscoelastic
describe viscoelastic?
inhibits both viscous and elastic characteristics when undergoing deformation
are lower viscoelastic materials more or less elastic ?
more elastic
which creates larger strain, sharply pulling the impression material from the patients mouth or gradually pulling the impression?
gradual pull
which properties affect accuracy of an impression?
viscosity - determines ability to flow over surface and record detail
setting mechanisms - does this cause dimensional contraction
thermal expansion coefficient - ideally low
hydrophobic/hydrophillic - affects surface contact
elasticity
tear strength
name 2 types of elastic impression materials?
hydrocolloids and elastomers
name an irreversible hydrocolloid?
alginate
which ions replace which in the alginate reaction?
calcium ions replace sodium
