Influence of Single-file Endodontics on Apical Transportation in Curved Root Canals: An Ex Vivo Micro–Computed Tomographic Study Alanna Junaid, BSc,* Laila Gonzales Freire, DDS, MSc, † Carlos Eduardo da Silveira Bueno, DDS, MSc, PhD, ‡ Isabel Mello, DDS, MSc, PhD, FRCD(C), § and Rodrigo Sanches Cunha, DDS, MSc, PhD, FRCD(C) § Abstract Introduction: More information regarding the ability of single files to maintain the original canal position is required before adopting a single-file approach to clean- ing and shaping. This study compares apical transporta- tion in curved root canals when instrumenting with a single WaveOne (WO) file (Dentsply Tulsa Dental Spe- cialties, Tulsa, OK) in a reciprocating motion with that incurred when using a sequence of Twisted Files (TFs; SybronEndo, Orange, CA) in a continuous rotating mo- tion. Methods: Forty mesial canals of mandibular molars were evenly allocated into 2 balanced groups (n = 20) with a 17-mm average canal length and 20  average curvature. Canals were accessed in a conven- tional manner and instrumentation was completed with a single WO file or a series of TFs. The canals were instrumented according to the manufacturers’ pro- tocol. Apical transportation was assessed on a compar- ison of the pre- and postinstrumentation micro– computed tomographic scans at 1-, 2-, 3-, 4-, and 5-mm sections. One-way analysis of variance was per- formed to assess if a significant difference between sys- tems exists. Results: No significant difference (P > .05) was found between the WO and TF groups. Transporta- tion in the mesial direction was of greater magnitude than distal transportation for both files systems. The mean transportation in the mesial direction was 100.1  8.8 mm (WO group) and 101.0  10.9 mm (TF group) (P = .5), whereas distal transportation was found to be 80.9  14.6 mm (WO group) and 60.3  11.0 mm (TF group) (P = .3). Conclusions: The results suggest that no difference exists between the WO file system and the conventional multifile TF system when consid- ering apical transportation in curved canals. (J Endod 2014;40:717–720) Key Words Continuous rotating motion, micro–computed tomography, reciprocating motion, root canal preparation, transportation C anal shaping via mechanical instrumentation is considered to be one of the most difficult tasks in root canal therapy (1). Ideally, the canal should be enlarged and debrided evenly in all directions to allow for thorough disinfection while maintain- ing the canal’s original position. For endodontic treatment to be successful, it is essen- tial to maintain the original configuration of the root canal system without introducing any iatrogenic errors (2). Transportation of the canal increases the risk of blockage, perforation, and ledge creation and may also weaken the root structure (3). When the canal is transported from its original position, obturation also may be compro- mised, resulting in a poor apical seal (3). Furthermore, if the canal is inadequately cleaned and instrumented, apical periodontitis may persist (4). The need to enlarge curved canals, while at the same time preserve dental anat- omy, will always involve the challenge of selecting appropriate endodontic instruments (5). In 2008, SybronEndo (Orange, CA) presented Twisted Files (TFs), the first fluted nickel-titanium file manufactured by plastic deformation, which is a process similar to the twisting process that is used to produce stainless steel K-files. A heating and cooling process is used to create the R-phase, which requires the instrument to be twisted in order to create the cutting flutes (6). It was further claimed that this thermomechanical processing serves to raise the flexibility and the fracture resistance of the file (7). According to Gergi et al (8), the heat treatment, the twisting manufacturing process, and the advanced surface conditioning/deoxidation treatment to which the instruments are submitted significantly increase their flexibility and resistance to cyclic fatigue, allowing them to remain in a central position even in severely curved canals (9). In 2010, a reciprocating system called WaveOne (WO) was introduced by Dentsply Tulsa Dental Specialties (Tulsa, OK). These files are manufactured using the M-Wire thermal treatment process, which provides increased flexibility (9–13) and strength to assist in reducing the risk of cyclic fatigue and file separation. The WO files shape root canals using a reciprocating motion in which the file continuously changes its rotating direction during the shaping procedure with a larger rotating angle in the cutting direction and a smaller angle in the reverse direction. The use of a series of nickel-titanium files in continuous rotational movement has been shown to be an effective method of achieving optimal root canal shaping with less straightening and better-centered preparations of curved canals (14). The From the *University of Manitoba, Winnipeg, Manitoba, Canada; † University of Sao Paulo, Sao Paulo, Sao Paulo, Brazil; ‡ Centre for Dental Research, Sao Leopoldo Mandic, Campinas, Sao Paulo, Brazil; and § Department of Restorative Dentistry, University of Manitoba, Winnipeg, Manitoba, Canada. Address requests for reprints to Dr Rodrigo Sanches Cunha, Department of Restorative Dentistry, University of Manitoba, D226C 780 Bannatyne Avenue, Winnipeg, Manitoba R3E 0W2, Canada. E-mail address: rodrigo.cunha@ad.umanitoba.ca 0099-2399/$ - see front matter Copyright ª 2014 American Association of Endodontists. http://dx.doi.org/10.1016/j.joen.2013.09.021 Basic Research—Technology JOE — Volume 40, Number 5, May 2014 Single-file Endodontics on Apical Transportation 717