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Purpose: The purpose of this study is to measure and compare a degree of setting expansion of dental stone by time depending on the mixing methods and mixing ratios of dental stone, to compare the surface state of each specimen with the use of an optical camera with microscope, and thereby to provide a fundamental material for making dental prostheses. Methods: The test on setting expansion of dental stone is based on ISO 6873. With two different mixing ratios and three kinds of stone mixing methods, test groups were created, and a total of six types of specimens (N=30) were made. Based on the specimens, the setting expansion rate of each one was measured in each time slot of 24 hours, and the surface of the set stone was measured. Results: According to the analysis on setting expansion rate of stone, the setting expansion of the specimen that was created in the way of vacuum mixing at normal mixing ratio was 0.1944% at 120 minutes; the setting expansion of the specimen that was created in the way of vacuum mixing at the mixing ratio which was 40% higher than normal mixing ratio was 0.195% at 120 minutes; the setting expansion of the specimen that was created in the way of mixing with hands at normal mixing ratio and then removing bubbles in vacuum mixer was 0.196% at 120 minutes. Conclusion: The setting expansion rate of each dental stone specimen was significantly different with the lapse of time up to 24 hours(p<.001).