Unit II Impressions and Casts

what is preliminary impressions

diagnostic impression used to create a diagnostic cast

what is an impression

negative reproduction of oral tissues

what is a cast

a positive reproduction of oral tissues

what is an impression tray

tool that holds impression material in the mouth

what is a custom tray

impression tray made specifically for an individuals mouth

why are prelim impressions taken

reproduce oral tissues and create diagnostic casts for diagnosis and treatment planning

what material is alginate

irreversible hydrocolloid

important characteristics of alginate

mixed with water, sets quick, detailed, low to moderate tissue displacement

why can alginate distort

contains 80 percent water, can gain or lose water

syneresis

loss of water, shrinks

imbibition

absorption of water, expansion

how is alginate impression handled after removal

remove, rinse, disinfect, rinse, pour

how quick should alginate be poured

12 minutes

how long should alginate cast remain in contact w the impression

1 hour max

what is impression compound

modeling plastic and thermoplastic material

how does impression compound set

softens with heat and harden when cooled

what cause more tissue displacement (alginate vs impression)

impression compound

why id stability a problem w alginate

water gain and water loss

what happens to impression compound when cold

becomes brittle and distorted

basic process from impression to cast

disinfect, prepare, pour, separate, trim, evaluate

what should you look for after serperating alginate cast

complete anatomy, voids, defects

stock tray

pre formed tray available in standard shapes/sizes,

what are stock trays made of

metal or plastic

custom tray

customized tray build for the model of patients teeth

what are custom trays made of

resin and acrylic

what is blockout

prevents tray material from engaging unwanted undercuts

what is relief

provides space over designated areas

spacer

creates controlled space for impression material