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Gypsum produces a...

positive replication
models, casts, dies

Properties of gypsum

Strength and resistance
Compatability with impression materials
Ease of use
biologically safe

Gypsum is...

naturally occur
Calcium Sulfate Dihydrate

Type II


Type III


Type IV

Improved stone

Gypsum is produced by...



Heating gypsum and removing water

Physical differences in gypsum is due to...

Calcination process


First dental stone
Least expensive and weakest
thin consistency


used for diagnostic models and working casts
yellow in color

Improved Stone

Putty Like

Water/Powder Ratio

Amount and temperature effects

Mixing with water turns a heminhhydrate into a ________



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


Maxillary cast is shaped to a ____


Mandibular cast is shaped in a _____


The base of each arch should be ____ of the arch height


Bases should be ___ of the total occluded height


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

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