Fixed Q2 Flashcards
Once the impression is in stone what is it placed on
articultor
what material should the impression be poured up in
gypsum
Gypsum. when the semi hydrate is mixed with water, a suspension is formed that is ____ and ____
fluid and workable
the hemihydrate dissolves until what point
forms saturated solution
what does the hemihydrate solution precipitate out
dihydrate
Polymers…
Stone….
Wax…
shrink
expand
temp dependent
PIMWIC, what 2 stages shrink, what 2 expand?
Impression and Cast shrink
Mount and Investment Expand
Gypsum rxn: powder + water = stone + heat
or…
hemihydrate + water = dihydrate + unreacted hemihydrate + heat
In the gypsum rxn, there is dissolution of…
precipitation of….
as long as…
hemihydrate
dihydrate
new crystals form/current crystals grow
what is the use for slurry water
to make the stone set quicker
how is gypsum classified
1-5 for compressive strength
classify the following: mounting plaster, dental stone, model plaster, dental stone-high strength low expansion, dental stone-high strength high expansion
1,3,2,4,5
what is the difference between types 4 and 5
4 low expansion
5 high expansion
What does the slurry water add that makes the gypsum precipitate more quickly?
More sites of nucleation
Gypsum classificaiton, Type I
Type II
Type III
Type IV
Type V
mounting plaster
model plaster
dental stone
dental stone - high strength, low expansion
dental stone - high strength, high expansion
Describe the particles of Plaster (gypsum) Type I/II:
This is a _____ hemihydrate:
large, irregular particles
Beta
Describe the particles of Stone type III-V:
This is a ____ hemihydrate:
small, greater strength
alpha
3 effects of adding water to the gypsum powder:
Increases Setting time
Weaker
Less expansion
why is type 3 used for making dentures
the final step of denture making involves breaking the stone. type 3 is easier to break
what class of gypsum is used for making impressions on a pt and why
*diagnostic
III
cheaper
what class is used for crowns and bridges
4 or 5
what type of gypsum should be used for high shrinking base metals
type 5 because it can compensate because it has higher expansion
what type of gypsum does Ahwatukee lab use.
Excalibur - type IV
Why should a cast be soaked in water before trimming?
Easier to trim, clean up, rid of particles