Dental plaster is the most commonly used material in the laboratory. Dentists are more familiar with the use of impression plaster in the clinical setting. Dental stone is usually more expensive to produce than plaster and its use is restricted to circumstances requiring greater strength and surface hardness. Dental plasters conform to International Standard ISO 6873:1998 Dental gypsum products.

• Type 1. Impression plaster
• Type 2. Plaster
• Type 3. Dental stone
• Type 4. Dental stone, high-strength, low-expansion
• Type 5. Dental stone, high-strength, high-expansion

These products are produced through partial dehydration of gypsum. Irregular and porous forms of crystals of the hemihydrate produced are called dental plaster. Hemihydrates with more regular crystals are commonly referred to as dental stone. Hemihydrate crystals of a more regular nature can be obtained by adding gypsum to boiling CaCl₂ solution*. Dental stones are more expensive to produce than dental plaster. To distinguish between the natural white of both products, a dye is usually mixed with the powder to identify dental stones.