Impression Materials Flashcards
impression materials used to make a ____ of dental structures
negative mold
requirements of ideal impression materials
- low cost
- long shelf life
- biocompatibility
- pleasant to pt
- dimensionally stable
- good handling properties
water based impression materials
- alginates
- agar agar
irreversible hydrocolloid impression material or alginate impression material used to make impressions for:
- removable partial dentures
- preliminary impressions for complete dentures
- ortho models and study models
alginate impressions not used for:
crown and bridge impressions (lack of accuracy)
alginic acid is soluble in water and forms a ____
“sol”
a sol resembles a solution, but is made up of ____ dispersed in a liquid
colloidal particles
setting rxn for alginate is a sol to ___ transformation
gel
alginate reactants
sodium or potassium alginate (12-15%)
calcium sulfate dihydrate (8-12%)
alginate retarder which can be adjusted by manufacturer to make regular or fast sets
sodium phosphate (2%)
alginate reinforcing filler for strength and body; controls stiffness of set gel
diatomaceous earth (70%)
provides good surfaces on gypsum dies
potassium sulfate or alkali zinc fluorides (about 10%)
coloring or flavoring agents (traces) used for ____
esthetics
first reaction when mixing powder and water provides adequate ____
working time (sodium phosphate)
after sodium phosphate has reacted, remaining ____ reacts with ____ to form an insoluble ____ alginate, which forms a gel with the water
calcium sulfate; sodium alginate; calcium
lower W/P ratio increases:
strength, tear resistance, and consistency
lower W/P ratio decreases:
working/setting time and flexibility
time from beginning of the mix until the setting reaction dominates
working time
time from beginning of the mix until the setting reaction is over
setting time
problem with alginate impressions
dimensional stability- undergoes shrinkage or expansion upon loss or gain of water
loss of water to the surroundings
syneresis
pick up of water from the surroundings
imbibition
hydrophobic impression materials for better stability
polysulfides
polysiloxanes
polyethers
polysulfides are ___ molecular weight oligomers containing reactive ____ groups
low; mercaptan
polysulfides oxidized by ____ or ____ to form a polysulfide rubber with a water condensate
lead dioxide; copper hydroxide
in general ____ are more stable than alginates or polysulfides in transferring detail to model
polysiloxanes or silicones
silicones or polysiloxanes are ____ by chemically and dimensionally stable
hydrophobic
addition type silicones can be made hydrophilic by:
- addition of surfactant
- chemical incorp of hydrophilic moieties into silicone backbone
addition silicone is called ____
poly(vinyl siloxane) or vinyl polysiloxane
siloxane with terminal silane groups
part A
siloxane with vinyl terminal groups
part B
improving detail registration and detail transfer
surfactants and polyethers
polyethers have many of the same characteristics of ____
polysiloxanes
differences of polyethers
hydrophilic and bad taste
gypsum is the dihydrate form of ____, found in a compact mass in nature
calcium sulfate
gypsum products manufactured by driving off part of the ____ of the calcium sulfate dihydrate to form _____; this process is referred to as _____
water; calcium sulfate hemihydrate; calcination
plaster is composed of _____
the beta form of calcium sulfate hemihydrate crystals
stone is the ____ form
alpha calcium sulfate hemihydrate form
the principal difference bwteen plaster, stone, and high strength stone is in the _____
shape and form of the hemihydrate crystals
crystals of dental stone and high strength dental stone are more ____ and _____ in shape; this makes it possible to obtain the same consistency with less ____ with the stones than with plaster
dense; regular; excess water
biggest disadvantage of gypsum products
relatively poor resistance to abrasion
one way to improve abrasion resistance is to add “gypsum hardeners” like ____ or _____
colloidal silica; synthetic resin
directly proportional to W/P ratio
manipulation and setting times
inversely related to W/P ratio
strength and setting expansion
custom tray material that is visible light cured
TRIAD
____ in TRIAD provide hardness and rigidity to the tray
fillers
____ and ____ are provisional materials that use cold cure not light cure
trim; jet
curing is achieved by ____ or ____
mixing; working time
