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37 terms

OCC DHY 150 Gypsum Materials

STUDY
PLAY
Gypsum produces a...
positive replication
models, casts, dies
Properties of gypsum
Accuracy
Strength and resistance
Compatability with impression materials
Ease of use
biologically safe
Gypsum is...
naturally occur
Calcium Sulfate Dihydrate
Type II
Plaster
Type III
Stone
Type IV
Improved stone
Gypsum is produced by...
Calcination
Calicination
Heating gypsum and removing water
Physical differences in gypsum is due to...
Calcination process
Plaster
First dental stone
Least expensive and weakest
thin consistency
Stone
used for diagnostic models and working casts
yellow in color
alpha-hemihydrate
Improved Stone
Putty Like
Water/Powder Ratio
Amount and temperature effects
Mixing with water turns a heminhhydrate into a ________
dihydrate
Exothermic
Heat is liberated during the reaction
Stone W/P ratio
100g/ 28-30 mL
Working or initial setting time
Length of time from the start of the mix until it reaches a semi-hard stage
Time allowed for manipulation
Final Setting Time
The length of time from the beginning of the mix until the mass has become ridgid
Loss of gloss
end of working time
5-7 mins.
Loss of exothermic reaction
end of setting time
30-40 mins.
Increasing Setting Time
Addition of borax
Increase water
cold water
less mixing
Decreased Setting Time
Addition of KSO4
Decrease water
Warm water
more mixing
Gypsum should be stored in an.....
air tight container
Hygroscopic expansion
When gypsum come in contact with water during the setting time
Alginate effects on gypsum
If alginate remains in a gypsum cast it may eat away the model
Add ____ to _____
dry; wet
Techniques for pouring study models
Double pour
single pour with wax base
single pour with base former
Double pour
Pour the positive replication of the oral cavity
Pour a base of gypsum and bind the two together
When forming a gypsum cast and base the base should be______ to the counter
parallel
Maxillary cast is shaped to a ____
point
Mandibular cast is shaped in a _____
horseshoe
The base of each arch should be ____ of the arch height
1/3
Bases should be ___ of the total occluded height
1/2
Ideal occluded cast height
2 1/2-3 inches
Maxillary cast trimming
Parallel to the central grooves of posterior teeth
Canine eminence to midline
Mandibular cast trimming
Canine to canine
Label casts with
Your name, patient's name, and date