Effects of heat in the properties of NaOCl alone and mixed with etidronate and alkaline tetrasodium EDTA.

AIM To assess the free available chlorine concentration (FAC), organic tissue dissolution, and smear layer removal capacity of sodium hypochlorite (NaOCl) alone and when mixtured with etidronate (HEDP) and tetrasodium EDTA (Na4 EDTA), and heated to different temperatures. METHODOLOGY Mixtures at 1:1 ratio of 5% NaOCl with distilled water (considered NaOCl alone), 18% HEDP or 10% Na4 EDTA were heated to 25 °C, 37 °C, 48 °C, and 60 °C. The FAC in the mixtures was assessed at 5, 10, 20, 30, 60, and 120 min. Samples of bovine muscle tissue (n=10) were prepared with similar size and weighed before and after 5, 10, and 15 min of immersion in the mixtures heated to the different temperatures to verify organic matter dissolution. The intergroup results were statistically compared by one-way analysis of variance (ANOVA) and intragroup by two-way analysis of variance (ANOVA), both followed by Tukey's multiple-comparison test (α 0.01). Smear layer removal by NaOCl alone was enhanced by heating resulting in lower score in some samples and became more rapid in the mixtures with the chelators. The saline solution did not promote tissue dissolution nor smear layer removal (P > 0.01). CONCLUSION In this laboratory study, heating NaOCl alone or when mixed with HEDP improved its capacity to dissolve organic matter and remove the smear layer. However, the mixture with HEDP required frequent refreshment to retain these effects when heated. Due to acceleration in the reaction between the irrigants, very rapid reductions in the free available chlorine in the mixtures with Na4 EDTA heated to the different temperatures occurred.