Impression Materials

Question 1

What do dimensional changes need to add up to?

Answer 1

zero

Question 2

What are the three types of impression materials?

Answer 2

rigid, plastic and (visco)elastic

Question 3

Viscoelastic impression materials are found as reversible (agar) or irreversible (alginate) ___.

Answer 3

hydrocolloids

Question 4

Viscoelastic impression materials can also be found as synthetic ___. These are ___ that polymerize into ___.

Answer 4

elastomers; oligomers; elastomers

Question 5

What are the different forms of synthetic elastomers?

Answer 5

polysulfide, silicone, polyether, and new product

Question 6

Which is the most common for of synthetic elastomer?q

Answer 6

addition silicone

Question 7

T/F. Light and heavy body impression materials are used separately to enhance the accuracy of the final impression.

Answer 7

False, they are used together.

Question 8

T/F. The light impression material is used for detail while the heavy is used in the other areas.

Answer 8

True.

Question 9

Define hydrocolloid.

Answer 9

Water is bound within a colloid matrix

Question 10

Both Alginate (___)(reversible/irreversible) and Agar (___) (reversible/irreversible) lack dimensional stability with time and require ___ pouring of models.

Answer 10

irreversible; reversible; immediate

Question 11

What type of polymer has no cross-linking and its physical state is reversibly controlled by temperature? For example, when heated it is fluid and when cooled it can be removed from the patient.

Answer 11

Thermoplastic

Question 12

A ___ polymer is transformed from monomer to polymer and involves irreversible ___.

Answer 12

Thermoset; cross-linking

Question 13

T/F. Condensation polymerization releases no by products.

Answer 13

False, addition polymerization releases no by-products whereas, condensation does.

Question 14

During the change from liquid or paste into a solid, advantageous final properties are ___ (increased/decreased).

Answer 14

increased.

Question 15

During the change from liquid/paste into a solid, the inherent density increase causes a volumetric ___ (shrinkage).

Answer 15

contraction

Question 16

During the change from liquid/paste into a solid, heat of reaction causes material to ___ ___, but this is usually minor.

Answer 16

heat up.

Question 17

During the change from liquid/paste into a solid, there is a ___ on cooling.

Answer 17

contraction

Question 18

Polysulfide low molecular weight oligomers containing reactive ___ groups.

Answer 18

mercaptan

Question 19

Polysulfide oxidized by lead dioxide or copper hydroxide to form a polysulfide ___ with a ___ condensate. This stains and does not taste good.

Answer 19

rubber; water

Question 20

T/F. For polysulfides to be accurate, this material requires a rigid custom tray for minimal thickness of impression materials.

Answer 20

True.

Question 21

T/F. Polysulfides recover from permenant deformation.

Answer 21

False, they do not recover from permanent deformation.

Question 22

T/F. Polysulfides should be poured as quickly as possible.

Answer 22

True.

Question 23

Silicones (Polysiloxanes) are inherently ___ but the addition type can be made more ___.

Answer 23

hydrophobic; hydophilic

Question 24

What was the first type of silicone introduced?

Answer 24

condensation

Question 25

How do you make the addition type of silicone more hydrophilic?

Answer 25

simple addition of surfactant or chemical incorporation of hydrophilic moieties into the silicone backbone.

Question 26

Fluid material needs a ___ contact angle, therefore you want it to be ___.

Answer 26

low; hydrophilic

Question 27

Why are contact angles important?

Answer 27

unset impression material over wet oral structures

unset gypsum-water mix into set impression

Question 28

Condensation silicone have low molecular weight oligomers containing reactive terminal ___ groups which react with ortho-ethyl silicate and stannous octoate to form the three dimensional network rubber with the liberation of ___ ___.

Answer 28

hydroxyl; ethyl alcohol

Question 29

With addition silicone, in the presence of ___ acid, ionic polymerization produces chain-lengthening and cross linking.

Answer 29

chloroplatinic

Question 30

With addition silicone, if there is residual ___ groups present from the mucosa, a secondary reaction occurs which produces ___ gas.

Answer 30

hydroxyl; hydrogen

Question 31

T/F. Pouring of addition silicone should be delayed.

Answer 31

True. It should be delayed until all of the hydrogen is liberated.

Question 32

What can contaminate addition silicone impression materials?

Answer 32

latex rubber gloves because of the sulfur

Question 33

If unmixed polyether contacts the skin or mucous membranes, this will cause contact ___.

Answer 33

dermatitis

Question 34

What are the four requirements of an ideal impression material?

Answer 34

1. low cost
2. long shelf life
3. biocompatibility
4. pleasant to patient

Question 35

What are the properties before setting?

Answer 35

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

Question 36

What are the properties during setting?

Answer 36

no dimensional change

short setting time

Question 37

What are the properties after setting?

Answer 37

1. high flexibility
2. high tear strength (a function of rate of strain)
3. no dimensional change
   - high elastic recovery
   - from applied stress
   - upon standing
4. compatibility with disinfectants
5. compatibility with die and cast materials
   - contact angle of gypsum-water mix
   - chemical interference
   - reproduction of fine detail