Correlative Bacteriologic and Micro–Computed Tomographic Analysis of Mandibular Molar Mesial Canals Prepared by Self-Adjusting File, Reciproc, and Twisted File Systems Jos e F. Siqueira, Jr, PhD,* Fl  avio R.F. Alves, PhD,* Marco A. Versiani, PhD, † Isabela N. R^ oc ¸as, PhD,* Bernardo M. Almeida, MS,* M^ onica A.S. Neves, PhD,* and Manoel D. Sousa-Neto, PhD † Abstract Introduction: This ex vivo study evaluated the disin- fecting and shaping ability of 3 protocols used in the preparation of mesial root canals of mandibular molars by means of correlative bacteriologic and micro– computed tomographic (mCT) analysis. Methods: The mesial canals of extracted mandibular molars were contaminated with Enterococcus faecalis for 30 days and assigned to 3 groups based on their anatomic configuration as determined by mCT analysis according to the preparation technique (Self-Adjusting File [ReDent-Nova, Ra’anana, Israel], Reciproc [VDW, Munich, Germany], and Twisted File [SybronEndo, Orange, CA]). In all groups, 2.5% NaOCl was the irrigant. Canal samples were taken before (S1) and after instrumentation (S2), and bacterial quantification was performed using culture. Next, mesial roots were subjected to additional mCT analysis in order to evaluate shaping of the canals. Results: All instrumentation protocols promoted a highly significant intracanal bacterial reduction (P < .001). Intergroup quantitative and qualitative comparisons disclosed no significant differences between groups (P > .05). As for shaping, no statistical difference was observed between the techniques regarding the mean percentage of volume increase, the surface area increase, the unprepared surface area, and the relative unprepared surface area (P > .05). Correlative analysis showed no statistically significant relationship between bacterial reduction and the mean percentage increase of the analyzed parameters (P > .05). Conclusions: The 3 instrumenta- tion systems have similar disinfecting and shaping performance in the preparation of mesial canals of mandibular molars. (J Endod 2013;39:1044–1050) Key Words Bacterial reduction, endodontic treatment, micro–computed tomography, reciprocating motion, Self-Adjusting File, single-file instrumentation T he primary goals of chemomechanical preparation are cleaning and shaping of the root canal (1). Although distinct, these objectives are achieved simultaneously during preparation through the use of instruments and irrigants. In infected root canals, disinfection is also required, and the best treatment outcome is usually achieved when root canal infection is eradicated or reduced to levels compatible with periradicular healing (2). Considering that remaining infection is an important risk factor for post-treatment apical periodontitis (3), chemomechanical preparation assumes a pivotal role in treatment because it acts mechanically and chemically on bacterial communities colonizing the main canal. Several studies have shown that, regardless of the instrumentation technique and instruments/irrigants used, chemomechanical procedures are unable to promote a thorough cleaning, disinfection, and shaping of the root canal, especially in curved canals or cases with unusual anatomies (4–8). Although the main canal and minor anatomic irregularities are generally incorporated into preparation, tissue remnants and bacteria present in other areas such as isthmuses, lateral canals, and apical ramifications usually remain unaffected by preparation because of inherent physical limitations of instruments and the short time of permanence of the irrigants within the root canal (8, 9). Besides, even areas of the main root canal have been shown to remain untouched by instruments (7). In order to circumvent such limitations and make cleaning, disinfection, and shaping more predictable, modifications in instruments and techniques have been devised. The Self-Adjusting File (SAF) (ReDent-Nova, Ra’anana, Israel) is an example of a modified instrument that has been designed to adapt to the main root canal anatomy (10). Studies have shown that the SAF promotes increased cleaning (11–13), disinfection (14), and shaping (15, 16) when compared with conventional endodontic instruments. The SAF is recommended to be used as a single-instrument technique, and, in this same line, other systems, such as Reciproc (VDW, Munich, Germany), have also been introduced. Unlike the SAF, these instruments have a helical shaft and are not substantially different from conventional rotary instruments but are proposed to be operated in reciprocating motion. Studies have shown that single-file instrumentation techniques using these helical instruments may promote cleaning From the *Department of Endodontics, Faculty of Dentistry, Est acio de S a University, Rio de Janeiro, Rio de Janeiro, Brazil; and † Department of Restorative Dentistry, Dental School of Ribeir~ ao Preto, University of S~ ao Paulo, Ribeir~ ao Preto, S~ ao Paulo, Brazil. Supported by grants from Fundac ¸ ~ ao Carlos Chagas Filho de Amparo  a Pesquisa do Estado do Rio de Janeiro and Conselho Nacional de Desenvolvimento Cient  ıfico e Tecnol ogico. Address requests for reprints to Dr Jos e F. Siqueira Jr, Est acio de S a University, Av Alfredo Baltazar da Silveira, 580/cobertura, Recreio, Rio de Janeiro, RJ, Brazil 22790-710. E-mail address: jf_siqueira@yahoo.com 0099-2399/$ - see front matter Copyright ª 2013 American Association of Endodontists. http://dx.doi.org/10.1016/j.joen.2013.04.034 Basic Research—Technology 1044 Siqueira et al. JOE — Volume 39, Number 8, August 2013