A slightly hydrated powder of alpha calcium sulfate that forms a dense stone‐like material when mixed with water. Used in dentistry to make casts. The alpha form of calcium sulfate is denser and superior to the beta form because it contains pieces and crystals in the form of rods or prisms.
A hemihydrate of gypsum divided into four classes according to the qualities resulting from differing methods of preparation. It is used in dentistry in the preparation of models and study casts.