Torsional Performance of ProTaper Gold Rotary Instruments during Shaping of Small Root Canals after 2 Different Glide Path Preparations Ana Arias, DDS, MS, PhD,* † Rafaela Andrade de Vasconcelos, DDS, MSc, PhD, ‡ Alexis Hern andez, DDS,* and Ove A. Peters, DMD, MS, PhD* Abstract Introduction: The purpose of this study was to assess the ex vivo torsional performance of a novel rotary sys- tem in small root canals after 2 different glide path prep- arations. Methods: Each independent canal of 8 mesial roots of mandibular molars was randomly assigned to achieve a reproducible glide path with a new set of either PathFile #1 (Dentsply Maillefer, Ballaigues, Switzerland) and #2 or ProGlider (Dentsply Maillefer) after negotiation with a 10 K-file. After glide path preparation, root canals in both groups were shaped with the same sequence of ProTaper Gold (Dentsply Tulsa Dental Specialties, Tulsa, OK) following the directions for use recommended by the manufacturer. A total of 16 new sets of each instrument of the ProTaper Gold (PTG) system were used. The tests were run in a standardized fashion in a torque-testing platform. Peak torque (Ncm) and force (N) were regis- tered during the shaping procedure and compared with Student t tests after normal distribution of data was confirmed. Results: No significant differences were found for any of the instruments in peak torque or force after the 2 different glide path preparations (P > .05). Data presented in this study also serve as a basis for the recommended torque for the use of PTG instruments. Conclusions: Under the conditions of this study, differ- ences in the torsional performance of PTG rotary instru- ments after 2 different glide path preparations could not be shown. The different geometry of glide path rotary systems seemed to have no effect on peak torque and force induced by PTG rotary instruments when shaping small root canals in extracted teeth. (J Endod 2016;- :1–5) Key Words Glide path, PathFile, ProGlider, ProTaper Gold, torque T he greater flexibility and cutting ability of nickel- titanium (NiTi) endodontic rotary instruments (1) have made them a popular tool to promote rapid and centered root canal shaping (2–4), but they tend to unexpectedly break because of flexural fatigue or torsional failure. Flexural fatigue is caused by the alternating tension-compression cycles to which they are subjected when flexed in the maximum curvature of the canal and rotated, whereas torsional failure occurs when the tip of the instrument binds, but the shank of the instru- ment continues rotating (5). NiTi endodontic instruments have evolved during the last 2 decades through the modification of cross-sectional designs and geometric properties. Improvement of the NiTi alloy with proprietary heat treatments has allowed the development of instru- ments with better flexural fracture resistance (6–12) although torsional performance seems not to show significant changes (13–18). Torque induced by a rotary instrument during root canal shaping depends mainly on the apical force applied to the instrument during canal preparation and the amount of contact between the instrument and the canal walls. Hence, the relation between the volume of the canal and the diameter of the instrument is relevant (19–21). The shaping technique used might play an important role in preventing torsional stresses. The creation of a glide path avoids the so-called screw-in effect (22) and the torsional breakage of instrument tips by reducing the risk of taper lock that occurs when the canal cross section is smaller than the tip of the instrument (21, 23). It has been traditionally advocated to explore and shape a root canal with a #15 hand instrument before the use of a rotary NiTi instrument to the full working length (24) to create a glide path for the safe advancement of the rotary instrument tip (25, 26). The creation of a rotary glide path has shown advantages compared with traditional hand file preparation (eg, better preservation of the canal anatomy and fewer aberrations) (27–29). In recent years, several new instruments with different geometries have been incorporated to achieve a glide path preparation before the use of rotary shaping instru- ments to the full canal length. PathFile (PF) was the first NiTi rotary system specifically designed to simplify the process of glide path preparation. The system consisted of 3 instruments with a square cross section and a 0.02 taper. PF #1 has a 13 tip size, PF #2 has a 16 tip size, and PF #3 a 19 tip size (30). Recently, ProGlider (PG) has been marketed. It is a single-file glide path instrument made of M-Wire alloy that fea- tures a variable progressive taper of 2%–8.5% with a tip size of 16.02. The manufac- turer advocates that it creates a glide path faster than hand files or any other alternative rotary glide path solutions (31). Nevertheless, it has been recently reported that multiple-instrument systems for glide path preparation induce lower peak torque and peak force than single-instrument systems that are subjected to greater force and torque. Single-instrument systems seem to increase the amount of contact with the canal walls because of the larger flute diameter of the instrument and the canal walls (32); however, it is still not known if the preparation that they achieve may reduce the From the *Department of Endodontics, University of the Pacific, Arthur A Dugoni School of Dentistry, San Francisco, California; † Department of Conservative Dentistry, School of Dentistry, Complutense University, Madrid, Spain; and ‡ Centro Universit ario Tiradentes, Maceio, Alagoas, Brazil. Address requests for reprints to Dr Ana Arias, Department of Conservative Dentistry, School of Dentistry, Complutense University, Plaza Ramon y Cajal s/n, Ciudad Universitaria, Madrid 28040, Spain. E-mail address: aariaspa@ucm.es 0099-2399/$ - see front matter Copyright ª 2016 American Association of Endodontists. http://dx.doi.org/10.1016/j.joen.2016.10.034 Significance Torsional profiles presented in this study serve as a basis for a safer and more effective clinical use of instruments with innovative characteristics after different glide path preparations. Basic Research—Technology JOE — Volume -, Number -, - 2016 Torsional Performance of PTG Instruments 1