Week 1 Ch 5: Impression Materials

impression materials

used to make replicas of teeth restorations and preparations made for restorative treatments and other supporting oral tissues both hard and soft; negative reproduction of the oral structure

diagnostic cast

positive replica of the teeth and surrounding oral tissue

die

replica of a tooth that has been prepared for a restoration

preliminary impressions

precursor to another treatment

final impressions

more accurate, to provide a good fit

bite registration

to establish the proper relation between a restoration or prosthesis and the opposing teeth and to help mount diagnostic casts in an articulator

elastic materials

hydrocolloids (agar, alginate), polyvinyl siloxane (pvs), polyether

inelastic material

older impression materials, seldom used (impression plaster, zinc oxide eugenol, impression wax)

hydrocolloids

water-based colloids that function as elastic impression materials

reversible, irreversible

what are 2 types of hydrocolloids

sol

liquid state in which colloidal particles are suspended; by cooling or chemical reaction, it can change into a gel

gel

a semisolid state in which colloidal particles form a framework that traps liquid (ig. jello)

reversible hydrocolloid

used over 60yrs; most popular type of elastic impression materials; takes accurate impressions of teeth and tissues with undercuts; main use for op and crown procedures; agar

irreversible hydrocolloid

alginate hydrocolloid; change from sol phase to gel phase; not accurate enough for final impressions

can use in wet environment; inexpensive, easy to manipulate

what are some adv of irreversible hydrocolloid?

syneresis, imbibition, poor tear strength, not accurate for final impressions

what are some disadv of irreversible hydrocolloids?

elastomeric material

similar to rubber; composed of a base and accelerator/catalyst; used where teeth are present and material flexibility is needed for removal from oral cavity, for imp of preparations and demanding or highly accurate reproductions

polysulfide

oldest of elastomers; aka mercaptan; hardens by chemical reaction; unpleasant taste, odor, stains clothing

silicone

designed to improve over polysulfide impressions; less viscosity; available as addition reaction and condensation reaction

condensation silicone

two paste system or paste liquid; easy to mix, pleasant tasting, odorless; mixing reaction causes ethyl alcohol to form and be released causing shrinkage of the impression; silica or copper carbonate is added as filler

added silicone

two paste system; no by products formed during mixing; expensive; popular for crown and bridge; lowest dimensional change of any of the rubber impression material

polyether

good alternative to polysulfide imp material; very accurate; used in crown and bridges; more hydrophilic than other elastomers; stiffest; difficult to remove from mouth esp areas with undercuts; short working and setting time

update

auto mix systems have been developed for light and regular bodied addition silicones; caulk gun automatically mixes base and catalyst through special tips; light cured polyether available in light and regular bodied

chroma

intensity or strength in colour; teeth are generally pale in colour

value

how light or dark the colour is; teeth have ranges in light scale; are determined by the way they reflect light

opaque

when the light is completely absorbed by the object

transparent

when the light passes directly through an object

metamerism

colours look different under different light sources

retainer

part of bridge that fits over the abutment

pontic

false/artificial tooth

abutment

supporting natural tooth