The endodontic treatment's success depends on root canal disinfection effectiveness (1). However, during chemical-mechanical preparation, instruments, irrigating auxiliary substances, and intracanal drugs may not reach all regions and structures of the complex root canal anatomy (2), especially the apical region and the dentinal tubules (3). It is well documented that 35% to 53% of the canal wall remains un-instrumented. Therefore, microorganisms found in these portions have a greater chance of survival (4).

Another factor that contributes to endodontic treatment failure is that root canal infections are mediated by biofilms (5). In fact, such structures confer greater adhesion and resistance of microorganisms on biological surfaces (6), which can lead to recurrent infections after an apparent cure (5).

Recurrent infections can evolve into pathologies such as apical periodontitis (7) or even require endodontic surgery (2), generating long-term pain and discomfort for patients (8). To address these issues, new methodologies to improve root canal disinfection, such as rotary and reciprocating instruments, have been applied (9). However, such techniques are not entirely effective. Numbers can be alarming, as only approximately 12.4% of the professionals who performed root canal treatments report never having faced complications (1).

In addition to such mechanical approaches, irrigation techniques have emerged based on agitating the irrigating solutions to improve substance diffusion (4), such as ultrasound, sonic irrigation, photodynamic therapy, and ablative laser (10). Nevertheless, the efficiency of these technologies is still controversial, as they present better disinfection near the vibration file but not in the apical regions, which can be explained by the complex anatomy of the root canals (10,11,12).

Iontophoresis is a non-invasive technique for drug delivery based on a mild electric current that increases the penetration of molecules, charged or not, into biological tissues (13) and has shown benefits in other areas of dentistry, such as hypersensitivity and anesthesia (14,15). Conversely to the mechanisms of other penetration enhancer technologies, iontophoresis is not dependent on a mechanical tissue abrasion for promoting drug distribution. Even though minor transitory changes may occur in the biological barrier subjected to the electrical current (16), greater drug penetration and distribution are reported besides the adjacent application sites (17). Similarly, its use can also be promising in endodontics, increasing the distribution of antimicrobial substances in root canals and other irregularities, and improving the disinfection of the endodontic space (18,19). Indeed, iontophoresis has been shown to improve the disinfection potential of copper and potassium iodide solutions applied in an ex vivo model of freshly extracted single-rooted teeth with the crown removed (18). Iontophoresis has also been used to deliver chitosan nanoparticles to human incisors contaminated with Enterococcus faecalis (19). Yet, nanoparticles are complex structures that could potentially obstruct root canals.

To take full advantage of iontophoresis, a proof-of-concept that such a technique increases the radial distribution of a model molecule is still necessary. Additionally, the critical parameters affecting drug distribution in the endodontic space are still unknown.

Therefore, this study aimed to evaluate the endodontic iontophoresis application and the influence of current density and application time in the methylene blue dye penetration into root canals and dentinal tubules of bovine teeth.