<p class="western" align="justify"><span style="color: #000000;"><span style="font-family: Arial, serif;"><strong>Objective</strong></span></span><span style="color: #000000;"><span style="font-family: Arial, serif;">: the purpose of this study was to evaluate the efficacy of disinfection of type III dental stone by immersion in 1% sodium hypochlorite and 0.25% peracetic acid at different </span></span><span style="font-family: Arial, serif;">periods of time (1, 5 and 10 min). </span><span style="color: #000000;"><span style="font-family: Arial, serif;"><strong>Material</strong></span></span><span style="color: #000000;"><span style="font-family: Arial, serif;"><strong>and</strong></span></span><span style="color: #000000;"><span style="font-family: Arial, serif;"><strong>Methods</strong></span></span><span style="color: #000000;"><span style="font-family: Arial, serif;">: s</span></span><span style="font-family: Arial, serif;">ilicon dies were previously infected with strains of </span><span style="font-family: Arial, serif;"><em>Bacillus subtilis</em></span><span style="font-family: Arial, serif;"> for 15 min. Then</span><span style="color: #000000;"><span style="font-family: Arial, serif;">, type III gypsum stone (Herodent, </span></span><span style="font-family: Arial, serif;">Vigodent COLTÈNE SA, Rio de Janeiro, Brazil</span><span style="color: #000000;"><span style="font-family: Arial, serif;">) was inserted </span></span><span style="font-family: Arial, serif;">into the cavities to obtain contaminated specimens. A sterile silicone die was used to obtain uncontaminated specimens. The specimens were separated into positive and negative control groups, and further divided into the following groups: blocks immersed in sterile physiologic solution for 1, 5 or 10 min; blocks immersed in 1% sodium hypochlorite for 1, 5 or 10 min; and blocks immersed in 0.25% peracetic acid for 1, 5 or 10 min. All the groups were double-plated and incubated at 37 ˚C for 24 h. </span><span style="color: #000000;"><span style="font-family: Arial, serif;"><strong>Results</strong></span></span><span style="color: #000000;"><span style="font-family: Arial, serif;">: t</span></span><span style="font-family: Arial, serif;">he results were expressed in colony forming units (CFU/ml) and the data were submitted to the Kruskal-Wallis test followed by Dunn’s test. The results showed that immersion in 1% sodium hypochlorite and 0.25% peracetic acid resulted in complete disinfection of the test specimens at all test periods (p < 0.01), whereas immersion in saline did not provide effective disinfection. </span><span style="font-family: Arial, serif;"><strong>Conclusion</strong></span><span style="font-family: Arial, serif;">: i</span><span style="color: #000000;"><span style="font-family: Arial, serif;">t can be concluded that both 1% sodium hypochlorite and 0.25% peracetic acid provided effective disinfection in dental stone specimens immersed in the solutions described above, at different periods of time.</span></span></p><p class="western" align="justify"><span style="color: #000000;"><span style="font-family: Arial, serif;"><strong>Keywords</strong></span></span></p><p class="western" align="justify"><span style="color: #000000;"><span style="font-family: Arial, serif;">Disinfection; Peracetic acid; Sodium hypochlorite; Stone casts.</span></span></p>