dental02.jpg (11342 bytes)Fundamentals of
Dental Materials

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Gypsum Products, Dental Waxes, and Impression Materials

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a. Uses. Artificial stone is used in making master casts and dies and for general laboratory use when a very hard, strong product is needed. Artificial stone particles are nonporous. Therefore, the finished product is hard and dense. This provides an excellent master cast for the fabrication of prosthetic restorations. The crushing strength of artificial stone is 7,500 psi.

b. Mixing. Artificial stone is mixed much like plaster of Paris. The average mixing ratio is 30 cc (cubic centimeters) of water to 100 grams of stone powder. This ratio may vary with different manufacturers. The required amount of water is placed in a rubber bowl. The stone powder is added slowly. (Incorporate all of the powder with water before spatulating.) Spatulation should be thorough without whipping the mixture. Whipping can trap air bubbles, thus weakening the cast. The bowl should be vibrated during the mixing to make air bubbles rise to the surface. Spatulation should be completed in 30 to 60 seconds; after that, the bowl should again be vibrated. The use of mechanical spatulation helps to reduce air bubbles.

c. Setting Time. The initial setting time for artificial stone is usually 8 to 10 minutes. The final setting time is 25 to 45 minutes depending on the type of stone mixed. The surface hardness of artificial stone can be increased by soaking the cast for several hours in a solution of borax.

David L. Heiserman, Editor

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Revised: May 22, 2017