Abstract
By employing instruments that measure setting expansions using a laser displacement sensor and trial programs made by Visual Basic, the effect of molds used in the measurement of setting expansions of the dental stone were investigated. Then, utilizing the vertically splittable mold, the setting behavior of three kinds of dental gypsum and two investments was investigated. At the setting time or the time which the dimensional change reached a minimum, greater shrinkage was observed in the vertically splittable mold and glass tube than that in the JIS mold. There was no significant difference in the values when minimum dimensional changes were subtracted from those after 120 minutes. From these results, the splittable mold was used to measure the dimensional changes of three kinds of dental gypsum and two investments. All materials shrank at the setting time or at the time of reaching the minimum value. High-level shrinkage was observed in the dental stone and cristobalite investment after 120 minutes, and marked expansion was noted only in the phosphate-bonded investment. The values of dimensional change after 120 minutes subtracted from the minimum value generated values similar to those observed in the JIS methods for all materials in this study. Therefore, by employing these values, the accurate analysis of the behavior of dimensional change became possible. From these results, the measurement method utilizing the lazer displacement meter and measurement program facilitated monitoring of the setting procedure, and measurement of the dimensional change with high-level accuracy.
