Shaping efficiency as a function of time of a new heat-treated instrument G. De-Deus 1 , F. G. Belladonna 1 , M. Sim~ oes-Carvalho 1 , D. M. Cavalcante 1 , C. N. M. J. Ramalho 1 , E. M. Souza 2 , R. T. Lopes 3 & E. J. N. L. Silva 4 1 Department of Endodontics, Fluminense Federal University, Niter oi, Rio de Janeiro; 2 Department of Dentistry II, Federal University of Maranh~ ao, S~ ao Lu  ıs; 3 Nuclear Engineering Program, Federal University of Rio de Janeiro, Rio de Janeiro; and 4 Department of Endodontics, Grande Rio University, Rio de Janeiro, Brazil Abstract De-Deus G, Belladonna FG, Sim~ oes-Carvalho M, Cavalcante DM, Ramalho CNMJ, Souza EM, Lopes RT, Silva EJNL. Shaping efficiency as a function of time of a new heat-treated instrument. International Endodontic Journal, 52, 337–342, 2019. Aim To assess the shaping ability of the new XP- endo Shaper instrument after different working times. Methodology Ten mesial roots of mandibular molars were scanned in a micro-computed tomo- graphic device and prepared using the XP-endo Sha- per instrument up to the working length (WL) according to the manufacturer’s recommendation. Then, each specimen was subjected to an extra 15, 30 and 45 s of active instrumentation at the WL. Postoperative scans were performed after canal prepa- ration at each time-point. Then, the registered pre- and postoperative datasets were examined to evaluate the percentages of volume and surface area of the instrumented canal, surface area of noninstrumented canal areas and the volume of removed dentine. Repeated measures general linear model was used to compare the differences in either the increase or the reduction of the parameters amongst the time-points. Alpha-error was set at 5%. Results Extending the period of XP-endo Shaper active instrumentation at WL significantly influenced several parameters such as volume (P < 0.001) and surface area (P < 0.001) of the instrumented canal, surface area of noninstrumented canal areas (P < 0.001), and volume of removed dentine (P < 0.001). Conclusions Extending the activation time of XP- endo Shaper instruments at WL resulted in a more comprehensive root canal preparation, increasing the volume and surface area of root canal preparation and the volume of removed dentine. Keywords: micro-CT, noninstrumented canal areas, removed dentine, shaping ability, XP-endo Shaper. Received 11 March 2018; accepted 14 August 2018 Introduction Micro-computed tomographic technology (micro-CT) has been used to evaluate the shaping ability of endodontic instruments during root canal preparation procedures (Paqu e et al. 2010, Paqu e & Peters 2011, Versiani et al. 2013, De-Deus et al. 2015). Overall, use of micro-CT revealed that 59.6%–79.9% of the dentinal walls remained untouched after preparation of oval-shaped canals, which is a critical challenge for any available shaping protocol (Paqu e et al. 2010, Paqu e & Peters 2011, Versiani et al. 2013, De-Deus et al. 2015). This considerable body of evidence high- lights the suboptimal standard of mechanical prepara- tion performed by the current nickel-titanium (NiTi) rotary and reciprocating systems. In fact, these sys- tems are able to mechanically act only on the central body of the canal lumen, leaving several areas of the canal walls untouched (Versiani et al. 2013, Zuolo et al. 2018). Optimal mechanical shaping should be Correspondence: Gustavo De-Deus, Department of Endodon- tics, Fluminense Federal University, Av. Henrique Dodsworth 85 Apto 808–Lagoa, Rio de Janeiro, RJ, ZIP CODE:22061- 030, Brazil (e-mail: endogus@gmail.com). International Endodontic Journal, 52, 337–342, 2019 © 2018 International Endodontic Journal. Published by John Wiley & Sons Ltd doi:10.1111/iej.13000 337