It is essential to remove all pulpal tissues, dentinal debris, and viable microorganisms from the root canal system during endodontic treatment. Since bacteria and their byproducts are the causative factors of pulpal and peri-radicular inflammation, their elimination is vital for successful endodontic treatment. Failure to effectively eliminate them could lead to persistent inflammation and impairment of healing [1]. Although proper canal instrumentation and adequate irrigation with sodium hypochlorite can decrease the number of bacteria, it cannot remove Enterococcus (E.) faecalis from the root canal entirely [1-2].<br /><br />Enterococcus faecalis is an anaerobic gram-positive coccus that normally commences in the human oral cavity, gastrointestinal tract, and vagina because it has demonstrated good adaptation to such environments with rich nutrient and low oxygen levels and complex ecology. Several studies showed that E. faecalis was found more in cases of failed endodontic treatment than in cases with primary infections. Among all the reported cases with post-endodontic therapy pain and infection, it has been observed that E. faecalis is the most commonly found, with high prevalence values reaching up to 90%. Among all cases with primary endodontic infection, E. faecalis was more likely to be associated with asymptomatic cases than with symptomatic ones [3-5].<br /><br />E. faecalis is an extensively evaluated biological indicator. Several laboratory studies tested the susceptibility of E. faecalis to endodontic treatment, which showed high resistance of E. faecalis to antimicrobial agents. Furthermore, E. faecalis can survive in very harsh environments, with poor nutrient supply and high alkaline pH reaching up to 11.5. The capacity of E. faecalis for growing as a biofilm on root canal walls and as a mono-infection in treated canals without synergistic support from other bacteria makes high resistance to antimicrobial agents a very resistance pathogen to root canal treatment [6-7].<br />1. An in vitro evaluation of the antibacterial efficacy of chlorine dioxide on E. faecalis in bovine incisors. Eddy RS, Joyce AP, Roberts S, Buxton TB, Liewehr F. J Endod. 2005;31:672–675. [PubMed] [Google Scholar]<br />2. In vitro evaluation of the antimicrobial activity of chlorhexidine and sodium hypochlorite. Vianna ME, Gomes BP, Berber VB, Zaia AA, Ferraz CC, de Souza-Filho FJ. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2004;97:79–84. [PubMed] [Google Scholar]<br />3. Microorganisms from canals of root-filled teeth with periapical lesions. Pinheiro ET, Gomes BP, Ferraz CC, Sousa EL, Teixeira FB, Souza-Filho FJ. Int Endod J. 2003;36:1–11. [PubMed] [Google Scholar]<br />4. Association of Enterococcus faecalis with different forms of periradicular diseases. Rocas IN, Siqueira JF Jr, Santos KR. J Endod. 2004;30:315–320. [PubMed] [Google Scholar]<br />5. Microbiology of endodontic infections. Singh H. https://scientonline.org/open-access/microbiology-of-endodontic-infections.pdf J Dent Oral Hyg. 2016;2:1–4. [Google Scholar]<br />6. Efficacy of sodium hypochlorite and chlorhexidine against Enterococcus faecalis--a systematic review. Estrela C, Silva JA, de Alencar AH, Leles CR, Decurcio DA. J Appl Oral Sci. 2008;16:364–368. [PMC free article] [PubMed] [Google Scholar]<br />7. Antimicrobial activity of sodium hypochlorite, chlorhexidine and MTAD®️ against Enterococcus faecalis biofilm on human dentin matrix in vitro. Murad CF, Sassone LM, Souza MC, Fidel RAS, Fidel SR, Junior RH. http://revodonto.bvsalud.org/scielo.php?script=sci_arttext&pid=S1984-56852012000200005 Rev Bras Odontol. 2012;9:143–150. [Google Scholar]<br />