Abstract
A wax-pattern like a crown must expand in the outer direction by expansion of investment during setting. Accordingly, to suppress the expansion of investment during setting, some load, which was estimated at the resistance of wax pattern against expansion of investment, was applied and the setting and hygroscopic expansion was measured. From this experiment, setting expansion of gypsum bonded investment decreased in proportion to the applied load. Hygroscopic expansion was influenced to a greater extent by the rate of increase of the applied load than that of setting expansion. On basis of a time-expansion curve, we described the time-expansion gradient (de/dt) curve and examined the effect of the applied load on maximum expansion gradient. It was found that the maximum gradient in hygroscopic expansion was significantly affected by the applied load.
