Impression Materials

Question 1

Do impression materials undergo contraction or expansion

Answer 1

contraction

Question 2

What is the classification of impression materials by physical condition after setting

Answer 2

visco-elastic

Question 3

Viscoelastic impression materials are what kind of material (2)

Answer 3

hydrocolloids

synthetic elastomers; oligomers polymerize into elastomers

Question 4

What are the two types of hydrocolloids

Answer 4

reversible (agar)

irreversible (alginate)

Question 5

What are the four types of synthetic elastomers

Answer 5

polysulfide
silicone (like poly vinyl siloxane)
polyether
chemical combination of silicone and polyether

Question 6

By using a light and head impression material together, what properties are you taking advantage of

Answer 6

Light; low consistency or viscosity and high setting contraction
high; high consistency or viscosity and low setting contraction

Question 7

Hydrocolloids lack what with time and require immediate pouring of models

Answer 7

dimensional stability

Question 8

This type of hydrocolloid is convenient and relatively inexpensive

Answer 8

alginate (irreversible)

Question 9

This type of hydrocolloid has good initial dimensional accuracy, but required dimensional stability

Answer 9

agar (reversible)

Question 10

This category of polymer contains no cross-linking; physical stage is reversibly controlled by temperature (wax)

Answer 10

thermoplastic

Question 11

This category of polymer the transformation from monomer to polymer involves irreversible cross-linking

Answer 11

termoset

Question 12

This type of polymerization releases no by-products; free-radical, ring-openingm ionic

Answer 12

addition

Question 13

This type of polymerization results in a by product

Answer 13

condensation

Question 14

What four physical phenomena occur during polymerization

Answer 14

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

Question 15

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

Answer 15

polysulfide

Question 16

Silicones (polysiloxanes) are hydrophobic or hydrophilic

Answer 16

hydrophobic; but addition type can be made more hydrophilic

Question 17

This is important for; unset impression material over wet oral surface, unset gypsum-water mix into set impression

Answer 17

contact angle

Question 18

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

Answer 18

condensation

Question 19

This type of material can undergo a secondary reaction which produces hydrogen as

Answer 19

poly-vinyl-siloxane

Question 20

This material may cause dermatitis, requires a rigid custom tray and tastes bad

Answer 20

polyether

Question 21

What are the four requirements for an ideal impression material

Answer 21

low cost
long shelf life
biocompatibility
pleasant to patient

Question 22

What three things are important properties before setting

Answer 22

ease of manipulation
control over working time
good wetting (low contact angle) on moist oral structures

Question 23

What two things are important properties during setting

Answer 23

no dimensional change

short setting time

Question 24

What five things are important properties after setting

Answer 24

high flexibility
high tear strength
no dimensional change (from applied stress, from upon standing)
compatibility with disinfectants
compatibility with die and cast materials