Disinfecting Effects of Rotary Instrumentation with Either 2.5% Sodium Hypochlorite or 2% Chlorhexidine as the Main Irrigant: A Randomized Clinical Study Isabela N. R^ oc ¸as, PhD, Jose Claudio Provenzano, PhD, M^ onica A.S. Neves, PhD, and Jose F. Siqueira, Jr, PhD Abstract Introduction: This randomized clinical study compared the antibacterial effects of irrigation with either 2.5% sodium hypochlorite (NaOCl) or 2% chlorhexidine (CHX) during the preparation of infected root canals with rotary nickel-titanium instruments. Methods: The root canals of 50 single-rooted teeth with apical peri- odontitis were prepared by using BioRaCe rotary instru- ments (FKG Dentaire, La Chaux-de-Fonds, Switzerland) and irrigation with either 2.5% NaOCl (n = 25) or 2% CHX (n = 25). Samples were taken from the canal at baseline (S1) and after (S2) chemomechanical prepara- tion. DNA was extracted from the clinical samples, and the reduction of the levels of total bacteria and streptococci was evaluated by means of a 16S ribosomal RNA gene-based quantitative polymerase chain reaction assay. Results: All S1 samples were positive for the presence of bacteria. After chemomechanical prepara- tion using either 2.5% NaOCl or 2% CHX, 44% and 40% of the root canals still had detectable bacteria, respectively. As for total bacterial counts, a mean num- ber of 3.7  10 5 bacterial cell equivalents was present in S1 samples from the NaOCl group, with a substantial reduction in S2 to a mean of 5.49  10 2 cell equivalents (P < .001). In the CHX group, a mean bacterial load of 8.77  10 4 cell equivalents occurred in S1, with a signi- ficant reduction in S2 to a mean of 2.81  10 3 cells (P < .001). The differences in both the presence/absence and quantitative data were not statistically significant (P > .05). Both irrigation protocols were highly effective in reducing the levels of Streptococcus species (P < .001). Conclusions: No significant difference was observed for the clinical antibacterial effectiveness of rotary preparation using either 2.5% NaOCl or 2% CHX as the main irrigant. (J Endod 2016;42:943–947) Key Words Apical periodontitis, chlorhexidine, endodontic treatment, root canal irrigation, sodium hypochlorite P roper control of the root canal infection is crucial for optimal treatment outcome (1, 2). Sterilization of the root canal system is virtually impossible to achieve with current instruments, substances, and techniques; thus, the major realistic microbiological goal of endodontic treatment is to reduce intracanal bacterial populations to levels that are compatible with periradicular tissue healing (3). Che- momechanical procedures play an essential role in reducing the bacterial burden in the main root canal, which is the area of the system that harbors the largest amounts of bacteria (4). The mechanical effects induced by instruments and the streaming of irrigants remove large amounts of bacteria, but the use of an antimicrobial irrigant solution is required to optimize disinfection (1, 5). For many years, sodium hypochlorite (NaOCl) has been the most commonly used endodontic irrigant. Its great acceptance among clinicians is related to its strong anti- bacterial and tissue-dissolving abilities (6, 7). However, NaOCl has some disadvantages, including tissue toxicity and development of serious complications when apically extruded (8, 9). This has prompted the search for alternative irrigants, such as chlorhexidine (CHX). CHX does not have tissue-dissolving ability but has good antibac- terial activity against oral bacteria (7, 10) and possesses the property of substantivity (11), which may result in prolonged antibacterial effects. Many in vitro/ex vivo studies have compared the antibacterial activities of NaOCl and CHX, some reporting that NaOCl is superior (7, 12, 13), some that CHX is superior (10, 14), and some that they are similar (15–18). As for clinical studies, comparative data are scarce and also inconclusive, as clearly shown by a recent systematic review (19). Of the studies using culture as the method of microbiologic analysis, 2 reported that NaOCl is superior (20, 21), and the other 2 showed no significant differences between them (22, 23). Of the molecular studies comparing the clinical antibacterial effects of the 2 substances, 1 showed no significant differences (24), whereas the other showed that NaOCl was superior (20). All these previous clinical studies used hand instrumentation, and so far no study has compared the antibacterial effectiveness of NaOCl and CHX as the irrigants using contemporary rotary nickel-titanium instruments. This clinical study was performed to compare the antibacterial effectiveness of 2.5% NaOCl and 2% CHX used as irrigants during the chemomechanical preparation of infected root canals associated with primary apical periodontitis lesions. The canals were From the Department of Endodontics, Faculty of Dentistry, Estacio de Sa University, Rio de Janeiro, Rio de Janeiro, Brazil. Address requests for reprints to Dr Jose Claudio Provenzano, Faculty of Dentistry, Estacio de Sa University, Av Alfredo Baltazar da Silveira, 580/Cobertura, Recreio, Rio de Janeiro, RJ, Brazil 22790-710. E-mail address: odontojcp@gmail.com 0099-2399/$ - see front matter Copyright ª 2016 Published by Elsevier Inc. on behalf of American Association of Endodontists. http://dx.doi.org/10.1016/j.joen.2016.03.019 Clinical Research JOE — Volume 42, Number 6, June 2016 Bacterial Reduction by NaOCl and Chlorhexidine 943