A slightly hydrated powder of beta calcium sulfate made from gypsum that forms a quick‐setting paste when mixed with water. Used in dentistry to make casts. The beta form of calcium sulfate is an aggregate of irregularly shaped porous fine crystals. Also known as plaster of Paris.
A powder, when mixed with water, that hardens to form a stonelike investment or model material. It is composed of a hemihydrate of gypsum (CaS04-2H20), which differs in compression strength and expansion coefficient according to how it is treated and rehydrated. There are four classes of dental plaster, with differing uses as materials for casts, impressions, or stone models, based on the differences of characteristics.