Impression Materials Flashcards
Do impression materials undergo contraction or expansion
contraction
What is the classification of impression materials by physical condition after setting
visco-elastic
Viscoelastic impression materials are what kind of material (2)
hydrocolloids
synthetic elastomers; oligomers polymerize into elastomers
What are the two types of hydrocolloids
reversible (agar)
irreversible (alginate)
What are the four types of synthetic elastomers
polysulfide
silicone (like poly vinyl siloxane)
polyether
chemical combination of silicone and polyether
By using a light and head impression material together, what properties are you taking advantage of
Light; low consistency or viscosity and high setting contraction
high; high consistency or viscosity and low setting contraction
Hydrocolloids lack what with time and require immediate pouring of models
dimensional stability
This type of hydrocolloid is convenient and relatively inexpensive
alginate (irreversible)
This type of hydrocolloid has good initial dimensional accuracy, but required dimensional stability
agar (reversible)
This category of polymer contains no cross-linking; physical stage is reversibly controlled by temperature (wax)
thermoplastic
This category of polymer the transformation from monomer to polymer involves irreversible cross-linking
termoset
This type of polymerization releases no by-products; free-radical, ring-openingm ionic
addition
This type of polymerization results in a by product
condensation
What four physical phenomena occur during polymerization
advantageous final properties are increased
the inherent density increase causes a volumetric contraction
heat of reaction causes material to heat up (minor)
contract upon cooling
This type of synthetic elastomer conforms well to a prepared tooth but requires a rigid custom tray for minimal thickness and does not recover from permanent deformation as well as some other impression materials
polysulfide
Silicones (polysiloxanes) are hydrophobic or hydrophilic
hydrophobic; but addition type can be made more hydrophilic
This is important for; unset impression material over wet oral surface, unset gypsum-water mix into set impression
contact angle
This type of silicone reacts with ortho-ethyl silicate and stannous octoate to from a 3D network rubber with liberation of ethyl alcohol; models should be poured as quickly as possible
condensation
This type of material can undergo a secondary reaction which produces hydrogen as
poly-vinyl-siloxane
This material may cause dermatitis, requires a rigid custom tray and tastes bad
polyether
What are the four requirements for an ideal impression material
low cost
long shelf life
biocompatibility
pleasant to patient
What three things are important properties before setting
ease of manipulation
control over working time
good wetting (low contact angle) on moist oral structures
What two things are important properties during setting
no dimensional change
short setting time
What five things are important properties after setting
high flexibility
high tear strength
no dimensional change (from applied stress, from upon standing)
compatibility with disinfectants
compatibility with die and cast materials
