The significance of precision in articulated cast interrelations is paramount to proper evaluation of occlusal disharmonies and laboratory fabrication of prosthodontic appliances. Peculiar dimensional phenomena associated with the setting of gypsum mounting agents generally cause discrepancies in cast relations through spatial displacement of the casts. Findings from preliminary studies on the contraction and expansion phases in setting gypsums indicate such displacement is attributable to changes during the contraction phase as well as the expansion phase. This study is designed to characterize the dimensional and thermal changes during the entire setting period by: 1) establishing in relation to time the magnitude of dimensional and thermal changes base autoclaved stone, 2) determination of the effect of exothermic heat on contraction and expansion dimensional changes, and 3) determination of the effects of water/powder ratios and chemical agents commonly used to modify gypsum setting time and expansion on normal dimensional and thermal patterns for setting gypsum. This experimentation is focused around a customized testing apparatus that employs three transducers simultaneously and a data acquisition module to process dimensional and thermal change signals. Findings, especially in respect to the setting contraction stage, could alter present principles applied in the formulation of dental gypsum products.
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