Effect of Adding some Additives and Drying Method on Compressive Strength of Gypsum Products

Abstract

Gypsum products (dental plaster and stone) are widely used in dentistry. However, the main problem with any gypsum products is reproduction of fine details and dimensional stability. The current study was conducted to assess the effect of incorporating various additives (i.e. cured resin, pulverised stone, pulverised plaster, and glass fibers) and drying method on compressive strength of gypsum products. A total of 160 specimens were divided into 2 groups according to the method of drying (air and microwave). For each drying method, each group was subdivided depending on the type of material used into 2 groups; dental plaster and dental stone. Variuos additives were used for reinforcement; cured resin, pulverised plaster, pulverised stone, and glass fibers. The unmodified group was considered as control. The specimens were dried and the compressive strength test was applied on all specimens. All specimens' data were statistically analysed via ANOVA, Tukey and independent T tests.The compressive strength of gypsum products was significantly influenced by the type of additive used. The specimens reinforced with glass fibers, cured resin, pulverised plaster, and stone had a greater value of mean compressive strength compared with unmodified groups. Statistically, highly significant differences were observed among all dried groups (P≤0.001). As well, the microwave specimens were more resistant to compressive loadings than air dried specimens. No significant differences, however, were recorded between the two drying methods (P>0.05).The glass fibers have a significant effect on compressive strength of gypsum products. The pulverised particles and cured resin can be added at 1 % by weight to enhance the mechanical properties of plaster and stone. Microwave drying for 5 minutes can fasten the drying time and permit early manipulation of plaster and stone models.