Gypsum products have a wide spectrum of uses in dentistry. In a previous study [1] four types of dental plasters were prepared using Egyptian gypsum raw material. Type I was prepared by calcination at 90 °C, Type II by heating gypsum to form soluble anhydrite which was rehydrated to the hemihydrate, Type III by autoclaving and Type IV by boiling in a saturated calcium chloride solution. Types I and II consists of p-hemihydrate while Types III and IV contains the a-modification [1]. The present work aims to assess the prepared plasters by the determination of the hydraulic, physico-me-chanical and microstructural properties. The results will be assessed in light of the ADA Specification NO. 25 [2].
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