We report on the effect of chemical disinfection in aqueous 1% virkon, 0·525% hypochlorite and slurry solutions on the mechanical and structural properties of type III and IV dental stones. For both dental stones, compressive strength and diametral tensile strength decrease with the application of all types of disinfectants. Virkon disinfectant decreases the mechanical strength with the lowest magnitude. The X-ray diffraction patterns of samples show the existence of dihydrate and hemihydrates microcrystals along with traces of CaSO4.xH2O (x = 0·02–0·48) in as prepared samples, but do reveal that hemihydrate phase is removed after spraying disinfectants. Fractography of the dental stones clearly indicates that the separation between the microcrystals is widened by the disinfection process as a consequence of the possible dissolution of last precipitated gypsum phases. The mechanical properties of the dental stones are effectively decreased after disinfection to different levels.
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