AbstractAimThe aim of this study was to determine the following: (i) the quantity of free chlorine in mixtures of equal proportions of sodium hypochlorite (NaOCl) with trisodium ethylenediaminetetraacetic acid (EDTAHNa3) and alkaline tetrasodium ethylenediaminetetraacetic acid (EDTANa4); (ii) organic matter dissolution; and (iii) the time necessary to remove the smear layer by these irrigants alone and when mixed.MethodologyThe solutions were mixed in a 1 : 1 ratio and then iodometrically titrated over time to determine the quantity of free available chlorine. The capability of organic matter dissolution by the solutions alone and the mixtures of irrigants was analysed by weighing bovine muscle tissue specimens before and after submission to the following groups (n = 10): G1 – 0.9% saline solution (control), G2 – 2.5% NaOCl, G3 – 17% EDTAHNa3, G4 – 10% EDTANa4, G5 – 20% EDTANa4, G6 – 5% NaOCl + 17% EDTAHNa3, G7 – 5% NaOCl + 10% EDTANa4 and G8 – 5% NaOCl + 20% EDTANa4. The times necessary for smear layer removal were determinated on discs of bovine dentine with a standardized smear layer produced with SiC papers using a scanning electron microscope that did not require the samples to be sputter coated. The dentine discs were submitted to the same experimental groups previously described (n = 10) over several time periods, and the photomicrographs acquired were scored for the presence of smear layer. The parametric data of tissue dissolution were analysed using two‐way anova and one‐way anova with Tukey's post hoc tests (α < 0.05), whilst nonparametric data of smear layer removal were analysed by Friedman test (α < 0.05) and the Kruskal–Wallis test with Dunn's post hoc (α < 0.05).ResultsEDTAHNa3 caused an almost complete and immediate loss of free available chlorine from NaOCl, whilst EDTANa4 promoted a slow and concentrat‐ion‐dependent decline. The organic matter was not dissolved in the control group, EDTA groups or the mixture of NaOCl + 17% EDTAHNa3 group (P > 0.05). NaOCl alone and the associations of NaOCl + EDTANa4 dissolved tissue at all periods analysed (P < 0.05). The smear layer was not removed in the control and NaOCl groups (P > 0.05). The smear layer was removed at 1 min in the NaOCl + 17% EDTAHNa3 group (P < 0.05); 2 min in 17% EDTAHNa3 group (P < 0.05); and 5 min in 10% EDTANa4, 20% EDTANa4, 5% NaOCl + 10% EDTANa4 and 5% NaOCl + 20% EDTANa4 groups (P < 0.05).ConclusionsAlkaline EDTANa4 was slower in removing the smear layer than EDTAHNa3, but when mixed with NaOCl during biomechanical canal preparation promoted organic matter dissolution and smear layer removal simultaneously. However, the mixing of NaOCl and EDTANa4 should be performed immediately before use to prevent the reduction of free available chlorine.