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


Gypsum products (dental plaster and stone) are widely used indentistry. However, the main problem with any gypsum productsis reproduction of fine details and dimensional stability. Thecurrent study was conducted to assess the effect of incorporatingvarious additives (i.e. cured resin, pulverised stone, pulverisedplaster, and glass fibers) and drying method on compressivestrength of gypsum products. A total of 160 specimens weredivided into 2 groups according to the method of drying (air andmicrowave). For each drying method, each group was subdivideddepending on the type of material used into 2 groups; dentalplaster and dental stone. Variuos additives were used forreinforcement; 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 wasapplied on all specimens. All specimens' data were statisticallyanalysed via ANOVA, Tukey and independent T tests.Thecompressive strength of gypsum products was significantlyinfluenced by the type of additive used. The specimens reinforcedwith glass fibers, cured resin, pulverised plaster, and stone had agreater value of mean compressive strength compared withunmodified groups. Statistically, highly significant differenceswere observed among all dried groups (P≤0.001). As well, themicrowave specimens were more resistant to compressiveloadings 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 compressivestrength of gypsum products. The pulverised particles and curedresin can be added at 1 % by weight to enhance the mechanicalproperties of plaster and stone. Microwave drying for 5 minutescan fasten the drying time and permit early manipulation of plasterand stone models.