Impression material (Inelastic) Quiz 2

Question 1

Inelastic impression plaster has little or no displacement of?

Answer 1

the tissues

Question 2

When salivation is excessive, you use inelastic or elastic impression materials?

Answer 2

Inelastic

Question 3

Inelastic impression materials used for _____ dentures for jaw relations

Answer 3

complete

Question 4

the setting time of plaster must be reduced to be used as an? This is accomplished how?

Answer 4

impression material. accomplished by adding certain chemicals to the powder, which cause a very rapid set to occur. Retarders are therefore also required in order to produce a reasonable working time

Question 5

Borax acts as a?

Answer 5

retarder

Question 6

higher W/P ratio results in increased setting time, but adversely affects the?

Answer 6

consistency of mix and the strength of set plaster

Question 7

KCL, K2SO4, KNO3 reduce?

Answer 7

expansion, reduce setting time

Question 8

A _____ ____ is necessary in order to separate a gypsum model from a gypsum impression.

Answer 8

separate media. They are varnishes or waxes dissolved in alcohol -too thick of a layer results in loss of detail reproduction

Question 9

Composit material is about 50-50 what?

Answer 9

filler and amorphous (or matrix)

Question 10

amorphous solid

Answer 10

• possesses a softening range

* placed in mouth at 113F and cooled to body temp at 98.6F

Question 11

Do distortions occur more readily in amorphous or crystalline solids?

Answer 11

amorphous

Question 12

Why is it important to pour casts with one hour?

Answer 12

Because trapped residual stresses will relieve themselves through distortion, pour quickly to minimize this issue

Question 13

Inelastic impression compounds have poor thermal conductivity. This means what?

Answer 13

the outside will heat and cool faster than the inside. You must allow time for the inside to reach desired temp

Question 14

Effects of wet kneading (there are two)

Answer 14

1) excessive will cause water to enter compound and more distortions after cooling
2) leaving in water too long or too hot will cause the compound to become brittle and grainy bc low MW components are leaked out

Question 15

ZOE stands for?

Answer 15

zinc oxide-eugenol

Question 16

what are the uses of ZOE?

Answer 16

1) impression paste
2) temporary crown and bridge cement
3) bite registration paste
4) periodontal dressings
5) temporary fillings
6) root canal cement

Question 17

Explain chemical reaction of ZOE

Answer 17

• *Autocatalytic - water is essential
  1) reaction takes place at surfaces of powder particles
  2) accelerated by increased temp, humidity, and Zn acetate
  3) ZnE2 is chelation bonded; not very stable and easily hydrolyzed

Question 18

ZnE2

Answer 18

product of ZOE reaction

*ZnE2 is chelation bonded; not very stable and easily hydrolyzed

Question 19

ZOE reaction

Answer 19

ZnO+H2O=Zn(OH)2

Zn(OH)2+2HE=ZnE2+2H2O

Question 20

Setting time: too slow? too fast? ZnO/Eugenol ratio?

Answer 20

• ) too slow= add Zn acetate in SMALL amounts (will drastically affect it)
• ) too fast= lower temp or humidity
• ) larger ratio- shorter setting time

Question 21

What is preferred over pure eugenal and why?

Answer 21

oil of cloves at 70-80% eugenal bc it reduces burning of soft tissue when the impression material is first placed

Question 22

What tube # contains that water and ZnO?

Answer 22

Tube 1