Lecture 5 Flashcards
classes and subclasses of impression materials
Rigid: ZOE, plaster
Plastic: Wax, Compound
Viscoelastic: hydrocolloid, elastomers
what’s req. for ideal impression materials?
low cost, long shelf life, pleasant to patient, biocompatible, good handling, and dimensionably stable
how does alginate form gel?
irreversible Ca2+ crosslinkage
what’s the base of alginates?
water
what’re dimensional stability probs w/ alginates?
syneresis- shrinkage from h2o loss
imbibition - expansion from h2o gain
advantages of alginates
cost taste ease hydrophilic, quick, stock trays, displaces blood/saliva
disadvantages of alginates?
single pour, quick pour, low dimenstional stability, low tear resistance, and low detail reproduction
how are polysiloxanes crosslinked?
hydrosilation rxn
polarity of polysiloxanes and it’s conseq.
hydrophobic, can cause voids in casts/stone
benefit of polysiloxanes over alginates
dimenstional stability
role of surfactants
make polysiloxanes more hydrophilic
polarity of polyethers
more hydrophilic than polysiloxanes but still hydrophobic.
characteristics of polyethers
good surface characteristics, and dimensional stability but bad taste
how do you cure gypsum?
water
gypsum is used for…
making models
