The effect of EDTA on the antibacterial activity of sodium hypochlorite

The combination of ethylenediaminetetraacetic acid (EDTA) and sodium hypochlorite (NaOCl) has been suggested as an irrigant for root canal therapy. However, the chemical interaction between these agents is a complex subject that is not completely understood. The aim of this study was to evaluate the interference of an EDTA chelating agent in the antibacterial ability of NaOCl, while also considering variations in methodology. Various concentrations of NaOCl and EDTA solutions were prepared from 6% and 17% solutions, respectively. The antibacterial potential of pure solutions and their combinations was assessed using a direct contact test against Enterococcus faecalis. In the first experiment, NaOCl and EDTA solutions were mixed 5 minutes before the addition of the E faecalis bacterial suspension. In the second experiment, both solutions were simultaneously put in contact with the bacterial suspension. Data were submitted to a Spearman correlation coefficient and chi-square test. Results indicated that growth of E faecalis was significantly dependent on the solution-mixing method. In the first experiment, high concentrations (17% and 8.5%) of EDTA prevented the complete killing of E faecalis by 6% NaOCl at all experimental timepoints. In the second experiment, all concentrations of NaOCl were able to eliminate E faecalis, even in the presence of EDTA. In conclusion, when NaOCl and EDTA were added simultaneously to a bacterial suspension without premixing, NaOCl was able to exert its full bactericidal action.