The effect of disinfectants on the properties of dental gypsum: 1. Mechanical properties.

Purpose: This study was conducted to evaluate the effect of selected disinfectants incorporated in the liquid of dental stones on material strength properties with the aim of developing a material with acceptable mechanical properties.

Materials And Methods: Two types of dental stone (types III and V) were mixed with aqueous solutions of 0.525% sodium hypochlorite, 0.1% and 10% povidone-iodine, and 2% glutaraldehyde, and with water as a control. The liquid/powder ratios recommended by the manufacturer were used. These materials were subjected to further modification by adding a mixture of 1.0% gum arabic and 0.132% calcium hydroxide to the hemihydrate powders before mixing with the disinfectant solutions at 2 different liquid/powder ratios for each. Both the regular and the modified materials were tested for compressive and diametral tensile strength after 1 hour and 1 week from the start of the mix. The structure of set materials was determined by scanning electron microscopy examination of fracture surfaces.

Results: The disinfectants often reduced the strength of both types of dental stone. However, using either 0.1% povidone-iodine or 0.525% sodium hypochlorite resulted in strength values comparable with that of the control. The addition of gum arabic and calcium hydroxide helped reduce the mixing liquid/powder ratios, improving the strength properties of the disinfected materials.

Conclusions: Chemical disinfectants reduce the strength of dental gypsum when used as mixing water substitutes. Gum arabic and calcium hydroxide additives permit a lower liquid/powder ratio and can help offset this weakening.