ORIGINAL RESEARCH Influence of EDTA and dentine in tissue dissolution ability of sodium hypochlorite Luiza Helena Silva de Almeida, DDS 1 ; Natália Gomes e Silva Leonardo, DDS 1 ; Ana Paula Neutzling Gomes, PhD 1 ; Erick Miranda Souza, PhD 2 ; and Fernanda Geraldes Pappen, PhD 1 1 Department of Semiology and Clinics, Faculty of Dentistry, Federal University of Pelotas, Pelotas, Brazil 2 Florence Institute, São Luís, Brazil Keywords EDTA, dentine, sodium hypochlorite, tissue dissolution. Correspondence Prof. Fernanda Geraldes Pappen, Division of Endodontics, Faculty of Dentistry, Federal University of Pelotas (UFPel), Rua Gonçalves Chaves 457–507, Pelotas, RS 96015-560, Brazil. Email: ferpappen@yahoo.com.br doi:10.1111/aej.12044 Abstract This study verified whether ethylenediaminetetraacetic acid (EDTA) influences the pulp tissue dissolution capability of different concentrations of NaOCl, in the presence of dentine. NaOCl and EDTA solutions were simultaneously mixed in flasks either containing a dentine disc or those not containing a dentine disc. Previously weighed bovine pulp tissues were immersed in the solutions for 5, 15 and 30 min. The weight loss was measured. The dissolution tests were performed in triplicate. Univariate analysis of variance, along with further Tukey’s honestly significant difference pairwise comparisons, was used to verify the effect of EDTA, different concentrations of NaOCl, dentine and time of incubation on the tissue dissolution. Higher concentrations of NaOCl increased the tissue dissolution. EDTA reduced the capacity of NaOCl to dis- solve pulp tissue, even in presence of dentine. Dentine negatively affects the capacity of NaOCl to dissolve pulp tissue. In conclusion, the presence of EDTA and dentine negatively affects the tissue dissolution ability of NaOCl. Introduction Since its introduction for endodontic therapy, almost a century ago (1), sodium hypochlorite (NaOCl) has remained the leading endodontic irrigant due to its soft tissue-dissolving and antimicrobial abilities (2–5). Both properties of NaOCl solutions are believed to be a func- tion of available chlorine (HOCl and OCl-) (2,6–8), which can be influenced and vary according to concentration, temperature, contact time, agitation, contact area and pH of the solution (9–11). Sodium hydroxide (NaOH) is also believed to dissolve organic tissue via saponification of fats (11,12), although negligible due to the low levels of NaOH found in NaOCl solutions (13). Since hypochlorite solutions have an insignificant dissolution effect on smear layer and dentine (7), demineralising agents, such as ethylenediaminete- traacetic acid (EDTA), which has a calcium-chelating capability, have been widely recommended as adjuvants in root canal therapy with the rationale to allow for a deeper penetration of NaOCl into dentine, resulting in more efficient cleansing of the root canal (14). Nevertheless, there appears to be no agreement in the literature on the most efficient sequence in which the two solutions (NaOCl and EDTA) should be used (15,16). Byström and Sundquist (17) recommended the alternating use of these solutions with the claim that this sequence is more efficient in reducing bacterial load in the root canal than the use of NaOCl alone through- out preparation. More recently, it has been shown, however, that mixing NaOCl with EDTA reduced the tissue-dissolving capability of NaOCl due to the reduc- tion of available chlorine (6,8), which may also hamper, in turn, the antimicrobial effectiveness of the solution (6). The exact mechanism by which EDTA reduces the amount of available chlorine is still unknown. However, it is interesting to highlight that EDTA is capable of main- taining its calcium-chelating efficacy even in the presence of NaOCl (6,18). The non-colloidal organic chelating Aust Endod J 2013 1 © 2013 Australian Society of Endodontology