Endodontic treatment has as main objective the effective decontamination of the root canal system, taking care not to induce damages to adjacent tissues, since microorganisms represent the major reason for pulp and periapical pathologies (Kakehashi, Stanley, & Fitzgerald, 1965), and chemical auxiliary substances induce inflammatory reactions when contacting connective tissue (Gatot, Arbelle, Leiberman, & Yanai-Inbar, 1991). The root canal instrumentation alone is not able to reach effective decontamination, due to the anatomical complexity of the root canal system (Ahmed et al., 2017, Gomes et al., 2023), which provides a suitable environment for microbial survival and development of persistent infection (Siqueira and Rôças, 2008). In this scenario, mechanical instrumentation must be associated with chemical auxiliary substances, in order to promote effective antimicrobial activity with no damage to adjacent tissues, favoring apical healing.

Sodium hypochlorite (NaOCl) and chlorhexidine (CHX) have been used as chemical auxiliary substances during chemomechanical preparation (Elgawish, Tawfik, El Gendy, George, & Bakr, 2023). The broad-spectrum antimicrobial activity (Du et al., 2012) and ability to promote pulp tissue dissolution (Okino, Siqueira, Santos, Bombana, & Figueiredo, 2004) are the main benefits of NaOCl. However, it induces significant modifications in organic components and mechanical properties of the root dentin (Moreira et al., 2009) and its cytotoxicity induces periapical tissue irritation (Gatot et al., 1991). In turn, CHX presents broad spectrum antimicrobial activity and substantivity, ensuring long time of action inside the root canal (Ferraz, Gomes, Zaia, Teixeira, & Souza-Filho, 2001). However, CHX is not able to promote pulp tissue dissolution (Okino et al., 2004) and induces some levels of inflammatory reaction when contacting connective tissues (Pereira et al., 2013). Therefore, there is a constant search for new alternatives in the field of auxiliary chemical substances (Souza et al., 2023).

More recently, a new technology called Dentaqua (Dentaqua, Conmel, Ireland) has been developed, which has the ability to produce hypochlorous acid (HClO) solution at different concentrations. It is obtained by the electrolysis of saline solution mixed with distilled water and previous studies have shown its antimicrobial potential in dental unit water lines (Marais and Brözel, 1999, Shajahan et al., 2016), as well as its low cytotoxicity when tested over epithelial tissues (Boyle et al., 2010, Sismanoglu and Ercal, 2022). In addition, HClO has both proinflammatory and anti-inflammatory properties, promoting healing from inflamed areas of periodontal tissues by regulating cytokines and growth factors (Sam and Lu, 2009, Nani et al., 2022). Although these previous results of the literature reveal a promising future for the use of HClO, its antimicrobial activity in root canals and cytotoxicity potential over connective tissue cells need further investigations.

Thus, the aim of this study was to perform an in vitro evaluation of the antimicrobial effect of HClO obtained from an electrolytic device on root canals infected with Enterococcus faecalis (E.faecalis) and its cytotoxicity in fibroblastic cells. The null hypotheses were that (i) HClO does not present antimicrobial activity and (ii) high cytotoxicity, when compared to other chemical auxiliary substances under investigation.