hard replicas of hard and soft tissue of the pts oral cavity made from gypsum products also referred to as models
casts
the weakest most porous form of gypsum product used in dentistry
model plaster
a stronger less porous form of gypsum than model plaster that is used in dentistry
dental stone
replicas of the prepared teeth that are general removable from working cast
dies
the densest form of gypsum product used in dentistry
die stone
casts genreally made from dental plaster or stone and used for pt education, treatment planning and tracking the progress of treatment as with orthodontic models these casts are also know as study models
diagnostic casts
casts generally made from one of the dental stones that are strong enough to resist the stresses of fabricating an indirect restoration or prosthesis these casts are also known as master casts
working casts
pouring the cast referes to the process of vibrating the flowable gypsum product into the impression this process must produce a cast that is the exact replica of the impression
pouring
the precess of removing excess hardened gypsum from the cast for ease in working with the cast and appearance in presentation
trimming
what mineral do you start with?
calcium sulfate Di-hydrate
what is the formula for calcium suflate di-hydrate
CaSO4 2 H2O
what type of gypsum has the highest setting expansion?
plater type II gypsum
what type of gypsum has a low setting expansion
stone type III gypsum
plaster type II is a ____ calcium sulfate hemi-hydrate
beta
what is the w/p ratio for plaster type II gypsum
0.45
stone type III gypsum is a _____ calcium sulfate hemi-hydrate
alpha
what is the water to powder ratio for stone type III gypsum
0.30
what is the difference in the water content of the types of gypsum?
lots of water is neeeded to turn into a di-hydrate, it is very porous and soaks up water.
t/f it takes more water to take a type II mpression than a type IV why?
true
takes more or less water to turn it into a di-hydrate
die stone, type IV gypsum is an ____ calcium suflate hemi-hydrate
alpha
what type of gypsum has the highest compressive strength, is the most wear resistant and has the lowest expansion?
die stone, type IV gypsum
what is the water to powder ratio for die stone, type IV gypsum
0.23
die stone, type IV gypsum has the best _____ detail with PVS which is an _____ silcon
surface
addition
t/fpowder is sifted into the water
true
what happens if spatulation is increase?
shortens setting time
increases rate setting expansion
properties of gypsum products are ______ related to their water to powder ration
DIRECTLY
an increase in water causes what three things?
weaker
less accurate model
longer set time
what is the initial set time for regular set products?
7-9 minutes
what is a sign that initial set has begun
loss of glossy appearance
why type of reaction happens during the final setting time?
exothermic reaction
how long must you wait before separation?
1 hour
waiting 24 hours the model is now ____times harder
3
failure to separate model within _____ will have detrimental effects on characteristics of model?
1 hour
what is slurry water?
set gypsum (CaSO4) particles in runoff water from trimming
if changes are made in the final setting time one sacrifices ____ ____, ______ or _____ ____
working time
strength
setting expansion
how long must you wait for the second pour in the double pour technique?
10 minutes
t/f the gypsum can absorb the water from the air
true
what type of container do you want to store gypsum in?
air tight
___ exposure to gypsum accelerates set
air
prolonged air exposure ____ gypsum
retards
why must the mixing bowls and spatulas be meticulously clean?
if not it accelerates setting time
t/f put excess material down the drain
false! in the trash it does NOT drain
before trimming you must ____ the base of the stone model in _____ for __-__ minutes BEFORE trimming but NEVER ____ the anatomic portion
soak
water
5-10
soak
t/f the anatomic portion of the model must be soaked before trimming and never the base
false! soak base not anatomic portion
t/f you must soak the base after trimming
false- BEFORE
the base should be ___/___ of the model and the anatomic should be ___/___
1/3
2/3
the occlusal plane must be ______ to base
PARALLEL
how is the anterior of a maxillary trimmed
to a point
how is the madibular trimmed?
rounded from cuspid to cuspid
more ____=greater expansion and less strength
water
what are four things to describe plaster?
softer
less accurate
greater porosity=less surface detail
lower compressive strength
what are three characteristics of diestone
hardes
most accurate
highest compressive strength
what is added to accelerate set?
potassium sulfate
what is added to slow the set
borax
air incorporated with mix results in surface _____
irregularities
water should be _______ and gypsum should be _____ to mix
MEASURED
WEIGHED
the model base is trimmed to be _______ to midline between the central incisors
perpendicular
silicone and polyether impression + gypsum=____ ____ ___
best surface detail
plaster=
betta
stone=
alpha
t/f plaster is more soluble than stone
true
_____ exposing models to water for long periods of time
