Evaluation of Some Physical Properties of Die Stone Made From Local Raw Gypsum Material

Abstract

Aim:The aim of this study was to prepare die stone material by dehydration of the local natural raw gypsum in boiling with 30% calcium chloride solution , and then evaluated some physical properties of this prepared die stone. Materials and methods : The values of some physical properties of the prepared die stone in boiling with 30% calcium chloride solution which are water/powder ratio, setting time, and compressive strength were compared with that of three types of gypsum products commercial die stone, Elite type III dental stone and Iraqi plaster. The data were collected , mean and standard deviation were determined. Statistically, (ANOVA) and Dunnett Pairwise Multiple Comparison test were carried out to determine the significant differences at p≤ 0.05 Results: Results showed that there were no significant differences between the locally prepared die stone and the commercial one at p≤ 0.05 in water/powder ratio and setting time values, but it was significant difference in compressive strength. But there are a significant difference between the physical properties of the locally prepared die stone and Elite type III dental stone and Iraqi plaster. Conclusions: The results showed the physical properties of the locally prepared die stone approach the physical properties of the commercial product according to the recommendation of ADA for gypsum products.

"Influence of Water Type and Water/Powder Ratio on the Strength and Hardness of Type III and IV Gypsum"

“…As the excess water present within the crystals evaporates, the structure of the set gypsum cast becomes porous, and as the water/ powder ratio increases, so does the volume of porosities, reducing the strength of the material after it has dried, because fewer dihydrate crystals are available per unit volume [8,9,13,14]. Any increase in the water-powder ratio consequently increases the amount of water per unit volume of gypsum, thus decreases the crystallization nuclei per unit volume and therefore increases the setting time of the product [14][15][16][17]. Setting expansion is also inversely proportional to waterpowder ratio; increase in water powder ratio increases the volume of micro-porosities and consequently increases the setting expansion [18][19][20].…”