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 (Na(4)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% Na(4)EDTA were heated to 25 degrees C, 37 degrees C, 48 degrees C and 60 degrees 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 compared statistically using one-way analysis of variance (anova) and intragroup by two-way analysis of variance (anova), both followed by Tukey's multiple-comparison test (alpha < 0.01). Bovine dentine blocks (n = 10) were analysed by scanning electron microscopy before and after immersion in the mixtures, and the time taken to remove the smear layer from the surfaces of the samples was determined. The Friedman test was used to compare the scores of the same group (alpha < 0.01), and the Kruskal-Wallis test with Dunn's post hoc was used to compare the different groups (alpha < 0.01). Saline solution was used as a control in the experiments of tissue dissolution and smear layer removal, Results Heating NaOCl alone did not affect its FAC. The higher the temperature of the mixtures with the chelators, the lower the FAC. Organic tissue dissolution was improved by increases in temperature of NaOCl alone and its mixture with HEDP (P < 0.01); however, the mixture with Na(4)EDTA had no improvement (P > 0.01). Smear layer removal by NaOCl alone was enhanced by heating resulting in lower scores 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 the acceleration in the reaction between the irrigants, very rapid reductions in the free available chlorine in the mixtures with Na(4)EDTA heated to the different temperatures occurred.

Automated summary

The study evaluated the free available chlorine concentration, organic tissue dissolution, and smear layer removal capacity of sodium hypochlorite (NaOCl) alone and mixed with different chemicals heated to various temperatures. Heating NaOCl alone did not affect its free available chlorine concentration, while the mixtures with chelators showed lower free available chlorine with higher temperatures. Organic tissue dissolution improved with temperature increases for NaOCl alone and NaOCl mixed with HEDP, but not with Na(4)EDTA mixtures. Smear layer removal was enhanced by heating NaOCl alone and became more rapid in mixtures with chelators.