Evaluation of Thermal Effect, Setting Temperature of Plaster and Its Effect on the Softening of Wax on Various Gypsum Products after Adding Additives

摘要

Two types of plaster (Al-Ahliyah Plaster and Plaster of Paris) were used as an experimental group and two types of stones (Elite and Silky Rock) represented the control group. In addition, five chemical materials as additives were chosen in this study (gum Arabian, rosin, potassium sulfate, borax and ferric oxide) at 0.25% concentration. One or two of each above additives were added to dental plasters to prepare 1394 samples. This study included the evaluation of the following characteristics: W/P ratio, setting temperatures, setting time. The results of the above measurements were subjected to descriptive analysis (mean and standard deviation). One-way analysis of variance (ANOVA) showed that there is a significant difference among the experimental groups, Duncan’s Multiple Range Test was also used to show the level of significance presented in each group. It is concluded that both types of dental plasters produced setting temperatures are however lower than that of the dental stones (control group) and their setting temperatures are more suitable for wax pattern than that of stone, but with additives, the setting temperature will be increased. This belongs mainly to the changes in the chemical structure of the gypsum. Also the results showed that, the mechanical properties of Al-Ahliyah plaster (local plaster) could be improved by the addition of some additives such as resin and gum Arabian.