Comparison between setting time, setting expansion and compressive strength in gypsum casts produced by mixing of gypsum powder with distilled water and 0.5% of Sodium Hypochlorite

Previous studies have demonstrated that dental stone casts can be disinfected by replacing 10v% of required water with 5.25% sodium hypochlorite solution. This comparative study evaluated physical properties of dental stone models produced by replacing distilled water with sodium hypochlorite. In this in-vitro experimental study, a total of 45 dental stone models were produced in the following 3 groups. Group A included stone models fabricated by mixing 300g gypsum powder and 94 mm3 distilled water. Group B comprised of stone models produced by mixing 300 g gypsum powder and 94 mm3 diluted 0.5% sodium hypochlorite solution. The third group (C) included specimens produced by mixing 300 g gypsum powder and 90 mm3 distilled water. Setting time, setting expansion and compressive strength of specimens were measured and compared. All tests were carried out according to ADA Specification No.25. Obtained results were entered SPSS software. ANOVA was applied for the comparison of 3 groups and Tukey’s test was used for pair wise comparison. Replacing distilled water with sodium hypochlorite caused a statistically significant reduction in setting time (mean reduction of 515 s) and increased the compressive strength of samples (mean increase of 4.06 MPa). Setting time in group 2 specimens was shorter than that in group 3 samples but no statistically significant difference was noted in setting expansion of samples in the 3 groups. Replacement of distilled water with sodium hypochlorite had no adverse effect on setting time, setting expansion or compressive strength of dental stone casts and thus can be used as a suitable method for disinfection of casts in dental laboratories.