Impression Materials Flashcards Preview

Operative > Impression Materials > Flashcards

Flashcards in Impression Materials Deck (48)
Loading flashcards...
1
Q

impression materials used to make a ____ of dental structures

A

negative mold

2
Q

requirements of ideal impression materials

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

water based impression materials

A
  • alginates

- agar agar

4
Q

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

A
  • removable partial dentures
  • preliminary impressions for complete dentures
  • ortho models and study models
5
Q

alginate impressions not used for:

A

crown and bridge impressions (lack of accuracy)

6
Q

alginic acid is soluble in water and forms a ____

A

“sol”

7
Q

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

A

colloidal particles

8
Q

setting rxn for alginate is a sol to ___ transformation

A

gel

9
Q

alginate reactants

A

sodium or potassium alginate (12-15%)

calcium sulfate dihydrate (8-12%)

10
Q

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

A

sodium phosphate (2%)

11
Q

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

A

diatomaceous earth (70%)

12
Q

provides good surfaces on gypsum dies

A

potassium sulfate or alkali zinc fluorides (about 10%)

13
Q

coloring or flavoring agents (traces) used for ____

A

esthetics

14
Q

first reaction when mixing powder and water provides adequate ____

A

working time (sodium phosphate)

15
Q

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

A

calcium sulfate; sodium alginate; calcium

16
Q

lower W/P ratio increases:

A

strength, tear resistance, and consistency

17
Q

lower W/P ratio decreases:

A

working/setting time and flexibility

18
Q

time from beginning of the mix until the setting reaction dominates

A

working time

19
Q

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

A

setting time

20
Q

problem with alginate impressions

A

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

21
Q

loss of water to the surroundings

A

syneresis

22
Q

pick up of water from the surroundings

A

imbibition

23
Q

hydrophobic impression materials for better stability

A

polysulfides
polysiloxanes
polyethers

24
Q

polysulfides are ___ molecular weight oligomers containing reactive ____ groups

A

low; mercaptan

25
Q

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

A

lead dioxide; copper hydroxide

26
Q

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

A

polysiloxanes or silicones

27
Q

silicones or polysiloxanes are ____ by chemically and dimensionally stable

A

hydrophobic

28
Q

addition type silicones can be made hydrophilic by:

A
  • addition of surfactant

- chemical incorp of hydrophilic moieties into silicone backbone

29
Q

addition silicone is called ____

A

poly(vinyl siloxane) or vinyl polysiloxane

30
Q

siloxane with terminal silane groups

A

part A

31
Q

siloxane with vinyl terminal groups

A

part B

32
Q

improving detail registration and detail transfer

A

surfactants and polyethers

33
Q

polyethers have many of the same characteristics of ____

A

polysiloxanes

34
Q

differences of polyethers

A

hydrophilic and bad taste

35
Q

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

A

calcium sulfate

36
Q

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

A

water; calcium sulfate hemihydrate; calcination

37
Q

plaster is composed of _____

A

the beta form of calcium sulfate hemihydrate crystals

38
Q

stone is the ____ form

A

alpha calcium sulfate hemihydrate form

39
Q

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

A

shape and form of the hemihydrate crystals

40
Q

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

A

dense; regular; excess water

41
Q

biggest disadvantage of gypsum products

A

relatively poor resistance to abrasion

42
Q

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

A

colloidal silica; synthetic resin

43
Q

directly proportional to W/P ratio

A

manipulation and setting times

44
Q

inversely related to W/P ratio

A

strength and setting expansion

45
Q

custom tray material that is visible light cured

A

TRIAD

46
Q

____ in TRIAD provide hardness and rigidity to the tray

A

fillers

47
Q

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

A

trim; jet

48
Q

curing is achieved by ____ or ____

A

mixing; working time