How the NaOCl solution concentration and temperature impact chlorine levels, tissue dissolution and pH

This study analyzed the behavior of sodium hypochlorite (NaOCl) at various concentrations and temperatures in relation to free available chlorine (FAC), tissue dissolution (TD), and pH. NaOCl solutions (2.50%, 5.25%, and 8.00% w/v) and distilled water (H2O) were evaluated. Each solution was heated to different temperatures (25°C, 37°C, and 60°C) for periods of 5 minutes, 10 minutes, and 15 minutes. For tissue dissolution analysis, bovine tissue samples (n = 10) were immersed in each solution and weighed before and after the designated times. FAC and pH were measured after each heating time. Data normality and homoscedasticity were verified using the Shapiro-Wilk and Levene tests. Solubility data were analyzed using the Kruskal-Wallis test and the Dwass-Steel-Critchlow-Fligner post-hoc test, and pH data were analyzed using one-way ANOVA and the Tukey post-hoc test. FAC data were subjected to a Student's t-test (α = 0.05%). At 25°C, all NaOCl concentrations had similar dissolution effects (p>0.05) and were superior to H2O (p<0.05). At 37°C, the dissolution effect of 2.5% NaOCl was similar to water after 5 min (p>0.05). NaOCl at 5.25% and 8.00% dissolved 90-100% of the samples after 10-15 min (37°C and 60°C). FAC in 2.50% NaOCl decreased when heated (37°C and 60°C), and 5.25% NaOCl showed a FAC reduction at 60°C (p<0.05). NaOCl at 8.00% showed similar results at all temperatures (p>0.05). The pH decreased (p<0.05) at 37°C and 60°C. Increasing NaOCl concentration, temperature, and heating time enhanced the tissue dissolution effect. Higher temperatures also reduced the FAC concentration in 2.50% and 5.25% NaOCl, as well as the pH in all evaluated NaOCl concentrations.