Dental Gypsum Materials

Gypsum is used to create:
Impressions of edentulous arches (inelastic thermoset)
Study models
Composition of Dental Gypsum Products
Extracted from the mineral gypsum

Chemically all dental gypsum products are derived from calcium sulfate dihydrate (In its pure form is white in color)
Gypsum Composition
calcium sulfate dihydrate
Ca SO4 • 2 H2O
All dental gypsum products are produced through a process of heating gypsum and driving off part of the water of crystallization

The result is the driving off of 1 1/2 H2O

Products differ in characteristics due to the type of calcination process used
CaSO4 • 2H2O + heat forms CaSO4 • 1/2H2O
(Calcium sulfate hemihydrate)
Impression Plaster defined
AKA Type I gypsum product;
(for edentulous patients; usually mint flavored)
Plaster defined
AKA Type II gypsum product; beta-hemihydrate; model or lab plaster
Stone defined
AKA Type III gypsum product; alpha-hemihydrate; Trade names: Hydro cal, Capstone (also called Class I stone) Lab stone
Die Stone defined
AKA Type IV gypsum product;
modified alpha-hemihydrate;
improved stone; TM Density; Die keen (also called Class II stone) Die stone
Plaster Calcination
Heated in an open container
Stone Calcination
Steam under pressure in a closed container
Die Stone Calcination
Method uses a calcium chloride solution
Plaster characteristics
Powder is made up of porous, irregular particles
Stone characteristics
Powder particles are more regular and uniform in shape
Die stone characteristics
Powder particles are cuboidal in shape; densest of the products
Plaster strength
Weakest of the 3 products
Stone strength
Stronger than plaster
Die stone strength
Strongest of the products
least expensive
Die Stone
most expensive
Density of 3 gypsums:
equal weights, but different volumes.
Plaster uses:
Study models; to attach casts to the mechanical articulator
Stone uses:
Study models; casts for the fabrication of partial and complete dentures, and appliances like athletic mouthguards
Die stone uses:
Casts and dies for the fabrication of inlays and crowns
Powder + water + heat
All 3 of the products - when hydrated change back to the dihydrate
Plaster setting expansion
expands the most
Die stone setting expansion
expands the least
Reason why more water is used for setting reaction:
for manipulation of the material