Quantitative analysis of unreacted hemihydrate in set dental stone by adiabatic calorimetry

The unreacted hemihydrate in set dental stone was estimated quantitatively by means of specific heat measurements. With decreases in the water-to-powder ratio (W/P), increases were observed in the amount of unreacted hemihydrate in the set mass. These increases were marked in set stone with a W/P ratio less than 0.25. Furthermore, the amount of unreacted hemihydrate was higher in the interior of the dental stone than in the set surface. It is very difficult to attain a complete reaction, even with higher W/P ratios such as 0.8 in the dental mixing procedure.