A study on gypsum hardener. (5).

The purpose of this series of studies is to search for an effective gypsum hardener. In the present study, we picked up a new gypsum hardener, Plaster Aid®. This hardener was applicated to two kinds of dental stones and the effectiveness was examined mechanically and dimensionally. In addition, the influence of soaking in water was also studied.The following results were obtained.1. Compressive strength, surface hardness and marginal strength of die stones after application of the gypsum hardener increased 1.5-2.0 times than those before application. After soaking in water, both compressive strength and surface hardness decreased, but the specimens applicated with the gyspum hardener were less influenced.2. Surface accuracy of Plastone-L after application increased, and that of Vel-mix Stone decreased.3. Film thickness of Plaster Aid® was so thin that dimensional change of stone dies could not be detected.