Impression Materials

Question 1

impression materials used to make a ____ of dental structures

Answer 1

negative mold

Question 2

requirements of ideal impression materials

Answer 2

1. low cost
2. long shelf life
3. biocompatibility
4. pleasant to pt
5. dimensionally stable
6. good handling properties

Question 3

water based impression materials

Answer 3

• alginates

- agar agar

Question 4

irreversible hydrocolloid impression material or alginate impression material used to make impressions for:

Answer 4

• removable partial dentures
• preliminary impressions for complete dentures
• ortho models and study models

Question 5

alginate impressions not used for:

Answer 5

crown and bridge impressions (lack of accuracy)

Question 6

alginic acid is soluble in water and forms a ____

Answer 6

“sol”

Question 7

a sol resembles a solution, but is made up of ____ dispersed in a liquid

Answer 7

colloidal particles

Question 8

setting rxn for alginate is a sol to ___ transformation

Answer 8

gel

Question 9

alginate reactants

Answer 9

sodium or potassium alginate (12-15%)

calcium sulfate dihydrate (8-12%)

Question 10

alginate retarder which can be adjusted by manufacturer to make regular or fast sets

Answer 10

sodium phosphate (2%)

Question 11

alginate reinforcing filler for strength and body; controls stiffness of set gel

Answer 11

diatomaceous earth (70%)

Question 12

provides good surfaces on gypsum dies

Answer 12

potassium sulfate or alkali zinc fluorides (about 10%)

Question 13

coloring or flavoring agents (traces) used for ____

Answer 13

esthetics

Question 14

first reaction when mixing powder and water provides adequate ____

Answer 14

working time (sodium phosphate)

Question 15

after sodium phosphate has reacted, remaining ____ reacts with ____ to form an insoluble ____ alginate, which forms a gel with the water

Answer 15

calcium sulfate; sodium alginate; calcium

Question 16

lower W/P ratio increases:

Answer 16

strength, tear resistance, and consistency

Question 17

lower W/P ratio decreases:

Answer 17

working/setting time and flexibility

Question 18

time from beginning of the mix until the setting reaction dominates

Answer 18

working time

Question 19

time from beginning of the mix until the setting reaction is over

Answer 19

setting time

Question 20

problem with alginate impressions

Answer 20

dimensional stability- undergoes shrinkage or expansion upon loss or gain of water

Question 21

loss of water to the surroundings

Answer 21

syneresis

Question 22

pick up of water from the surroundings

Answer 22

imbibition

Question 23

hydrophobic impression materials for better stability

Answer 23

polysulfides
polysiloxanes
polyethers

Question 24

polysulfides are ___ molecular weight oligomers containing reactive ____ groups

Answer 24

low; mercaptan

Question 25

polysulfides oxidized by ____ or ____ to form a polysulfide rubber with a water condensate

Answer 25

lead dioxide; copper hydroxide

Question 26

in general ____ are more stable than alginates or polysulfides in transferring detail to model

Answer 26

polysiloxanes or silicones

Question 27

silicones or polysiloxanes are ____ by chemically and dimensionally stable

Answer 27

hydrophobic

Question 28

addition type silicones can be made hydrophilic by:

Answer 28

- addition of surfactant | - chemical incorp of hydrophilic moieties into silicone backbone

Question 29

addition silicone is called ____

Answer 29

poly(vinyl siloxane) or vinyl polysiloxane

Question 30

siloxane with terminal silane groups

Answer 30

part A

Question 31

siloxane with vinyl terminal groups

Answer 31

part B

Question 32

improving detail registration and detail transfer

Answer 32

surfactants and polyethers

Question 33

polyethers have many of the same characteristics of ____

Answer 33

polysiloxanes

Question 34

differences of polyethers

Answer 34

hydrophilic and bad taste

Question 35

gypsum is the dihydrate form of ____, found in a compact mass in nature

Answer 35

calcium sulfate

Question 36

gypsum products manufactured by driving off part of the ____ of the calcium sulfate dihydrate to form _____; this process is referred to as _____

Answer 36

water; calcium sulfate hemihydrate; calcination

Question 37

plaster is composed of _____

Answer 37

the beta form of calcium sulfate hemihydrate crystals

Question 38

stone is the ____ form

Answer 38

alpha calcium sulfate hemihydrate form

Question 39

the principal difference bwteen plaster, stone, and high strength stone is in the _____

Answer 39

shape and form of the hemihydrate crystals

Question 40

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

Answer 40

dense; regular; excess water

Question 41

biggest disadvantage of gypsum products

Answer 41

relatively poor resistance to abrasion

Question 42

one way to improve abrasion resistance is to add "gypsum hardeners" like ____ or _____

Answer 42

colloidal silica; synthetic resin

Question 43

directly proportional to W/P ratio

Answer 43

manipulation and setting times

Question 44

inversely related to W/P ratio

Answer 44

strength and setting expansion

Question 45

custom tray material that is visible light cured

Answer 45

TRIAD

Question 46

____ in TRIAD provide hardness and rigidity to the tray

Answer 46

fillers

Question 47

____ and ____ are provisional materials that use cold cure not light cure

Answer 47

trim; jet

Question 48

curing is achieved by ____ or ____

Answer 48

mixing; working time