Dimensional changes in dental stone and plaster.

THIS report presents a method of determining the dimensional changes in gypsum dental products, which avoids the disadvantages of previous methods and which provides extreme sensitivity. As part of the program of research on the gypsum products used in dentistry, a preliminary study was made of various physical properties. This study, which included strength, thermal expansion, setting expansion, and other related properties, soon made it apparent that very little was known about dimensional changes occurring in these products when they are subjected to the technics used in prosthetic dentistry. Inasmuch as the final accuracy of a restoration is controlled to a large extent by these changes in the investing materials, a program was set up to determine the dimensional changes which occur when plaster and stone are subjected to the conditions found in dental practice.