Impression material (Inelastic) Quiz 2 Flashcards
Inelastic impression plaster has little or no displacement of?
the tissues
When salivation is excessive, you use inelastic or elastic impression materials?
Inelastic
Inelastic impression materials used for _____ dentures for jaw relations
complete
the setting time of plaster must be reduced to be used as an? This is accomplished how?
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
Borax acts as a?
retarder
higher W/P ratio results in increased setting time, but adversely affects the?
consistency of mix and the strength of set plaster
KCL, K2SO4, KNO3 reduce?
expansion, reduce setting time
A _____ ____ is necessary in order to separate a gypsum model from a gypsum impression.
separate media. They are varnishes or waxes dissolved in alcohol -too thick of a layer results in loss of detail reproduction
Composit material is about 50-50 what?
filler and amorphous (or matrix)
amorphous solid
- possesses a softening range
* placed in mouth at 113F and cooled to body temp at 98.6F
Do distortions occur more readily in amorphous or crystalline solids?
amorphous
Why is it important to pour casts with one hour?
Because trapped residual stresses will relieve themselves through distortion, pour quickly to minimize this issue
Inelastic impression compounds have poor thermal conductivity. This means what?
the outside will heat and cool faster than the inside. You must allow time for the inside to reach desired temp
Effects of wet kneading (there are two)
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
ZOE stands for?
zinc oxide-eugenol
what are the uses of ZOE?
1) impression paste
2) temporary crown and bridge cement
3) bite registration paste
4) periodontal dressings
5) temporary fillings
6) root canal cement
Explain chemical reaction of ZOE
- *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
ZnE2
product of ZOE reaction
*ZnE2 is chelation bonded; not very stable and easily hydrolyzed
ZOE reaction
ZnO+H2O=Zn(OH)2
Zn(OH)2+2HE=ZnE2+2H2O
Setting time: too slow? too fast? ZnO/Eugenol ratio?
- ) too slow= add Zn acetate in SMALL amounts (will drastically affect it)
- ) too fast= lower temp or humidity
- ) larger ratio- shorter setting time
What is preferred over pure eugenal and why?
oil of cloves at 70-80% eugenal bc it reduces burning of soft tissue when the impression material is first placed
What tube # contains that water and ZnO?
Tube 1
