Chapters 8 & 27 Quiz 2 Flashcards
are impressions negative or positive reproductions?
negative
impressions can be used to create a _______ or _________ which is a positive reproduction
model or cast
used to carry the impression material into the mouth
impression trays
impression trays can be ________ or _________
sterilized or disposable
take an impression of a smaller area, but can impress the maxillary and mandibular arch simultaneously
triple trays
dispensed onto a tray or directly on teeth and patient bites down
bite registration
the type of impression material being used depends on the ______ of the impression being taken
purpose
prepared teeth typically have ________
undercuts
what is required to take impressions of prepared teeth?
more elastic material
impressions on edentulous areas do or do not require as much detail?
do not
what type of impression material is used on edentulous areas of the mouth?
inelastic material which is harder and more rigid
measure of a liquids ability to flow
viscosity
placed in the sulcus to pull the tissue away from a tooth during crown and bridge preparations
retraction cord
impression material mixed with water
aqueous
impression material mixed with something other than water
nonaqueous
what are the three types of impression materials?
- inelastic
- aqueous elastomeric
- nonaqueous elastomeric
these materials change from a viscous liquid state called sol, to a semisolid, rubbery state called gel
aqueous
what are the types of inelastic impression materials?
plaster, wax, and zinc oxide eugenol
irreversible hydrocolloid
alginate
set by chemical reaction to reach gelation
irreversible hydrocolloid
what are the types of aqueous elastomeric impression materials?
alginate and agar
reversible hydrocolloid
agar
reaches gelation by means of temperature changes
reversible hydrocolloid
melting and gelling at different temperatures is _______
hysteresis
are alginate or agar impressions more accurate
agar
potassium alginate which dissolves in water forming a _______ which is also known as a gel
sol
alginate powder contains what?
potassium alginate, silica, antimicrobial agents, and water
the contraction of a gel accompanied by the separating out of liquid
syneresis
the absorption of one substance by another
imbibition
it is important to limit the time that an impression is exposed to an aqueous disinfection solution because of _______
imbibition
models should be poured shortly after an impression is taken because of __________
syneresis
what are the types of non aqueous elastomeric impression materials
polysulfides, condensation silicones, polyethers, and addition silicones
how do polysulfides and condensation silicones set
via condensation polymerization
what does condensation polymerization produce as a by-product
water
what type of system is are polysulfides
paste-paste
what are more accurate than alginate but not as accurate as other nonaqueous elastomeric materials
polysulfides
what type of impression materials taste and smell bad
polysulfides
what by-product is produced with condensation silicones
alcohol
what type of impression material is cleaner but harder to use
condensation silicones
do condensation silicones have to be poured fast or slow
fast
how do polyethers set
via cationic polymerization
what is there by-product of polyethers
none
what type of impression material is clean, tastes bad, and expensive
polyethers
what is the post popular non aqueous elastomeric material
addition silicones
how do addition silicones set
via polymerization with no by-product
increase wetting and reduce bubbles in the stone when the impression is poured up
surfactants
what impression material has surfactants added to them?
addition silicones
what three impression materials are inelastic
plaster, wax or impression compound, and ZOE
each tray should extend ______ to include all teeth as well as the musculature and vestibule
facially
how many mm of depth of alginate should be provided beyond the occlusal surface and incisal edges
2-3 mm
what can be placed around the boarders of the tray to add length/depth
rope wax
should removable appliances be taken out before taking impressions
yes
what temp of water increases the setting rate
warmer
what water temp slows the setting reaction
cooler
speeds up reaction; warm water; also potassium sulfate
accelerator
slows down reaction; cooler water; also borax
retarder
where should a right handed operator stand when seating a mandibular tray
7 oclock
where should the operator stand when seating a maxillary tray
11 oclock
what percent humidity do impressions need to be kept in if not poured up immediately
100 %
