Effects of rapid burnout type gypsum-bonded investment on performance of castings. Part 1. Surface aspects and fit of crowns.

Rapid burnout type gypsum-bonded investment materials were developed to shorten the time required for dental casting procedures. With these materials, molds can be prepared by rapid heating at 700 degrees C for 30 min from 30 min after the start of mixing. When the investment block was rapidly heated at 700 degrees C, no fractures were observed in the rapid burnout type investments with one exception, while a conventional cristobalite investment broke into pieces shortly after being placed in the furnace. Casting fins were sometimes induced only for the material which showed fracturing on rapid heating. No practical problems were found in the surface roughness of the castings. The 30 min-setting expansion was significantly different among the materials although there were no differences in thermal expansion, and the material showing greater 30 min-setting expansion was efficient to obtain better fit of the crown as in the conventional casting procedures.