Micro–computed Tomography Assessment of Dentinal Micro-cracks after Root Canal Preparation with TRUShape and Self-adjusting File Systems Mario Luis Zuolo, DDS, MSc,* Gustavo De-Deus, DDS, MSc, PhD, † Felipe Gonc ¸alves Belladonna, DDS, MSc, † Emmanuel Jo~ ao Nogueira Leal da Silva, DDS, MSc, PhD, ‡ Ricardo Tadeu Lopes, DDS, MSc, PhD, § Erick Miranda Souza, DDS, MSc, PhD, jj Marco Aur elio Versiani, DDS, MSc, PhD, ¶ and Alexandre Augusto Zaia, DDS, MSc, PhD* Abstract Introduction: The aim of the present study was to eval- uate the percentage frequency of dentinal micro-cracks observed after root canal preparation with TRUShape and Self-Adjusting File (SAF) systems by means of mi- cro–computed tomography imaging analysis. A conven- tional full-sequence rotary system (BioRace) and a single-file reciprocation system (Reciproc) were used as reference techniques for comparison because of their known assertive cutting efficiency. Methods: Forty anatomically matched mandibular incisors were selected, scanned at a resolution of 14.25 mm, and as- signed to 4 experimental groups (n = 10), according to the preparation protocol: TRUShape, SAF, BioRace, and Reciproc systems. After the experimental proced- ures, the specimens were scanned again, and the regis- tered preoperative and postoperative cross-section images of the roots (n = 70,030) were screened to iden- tify the presence of dentinal micro-cracks. Results: Overall, dentinal defects were observed in 28,790 cross-section images (41.11%). In the TRUShape, SAF, BioRace, and Reciproc groups, dentinal micro-cracks were visualized in 56.47% (n = 9842), 42.38% (n = 7450), 32.90% (n = 5826), and 32.77% (n = 5672) of the slices, respectively. All dentinal defects observed in the postoperative data sets were already present in the corresponding preoperative images. Con- clusions: None of the preparation systems induced the formation of new dentinal micro-cracks. (J Endod 2017;43:619–622) Key Words Dentinal defects, instrumentation, micro-cracks, micro-CT, root canal preparation V ertical root fracture is a clinical complication that may lead to tooth extrac- tion (1) and has been described in either treated or non-endodontically treated teeth (2, 3). During the last few years, several studies have reported a causal relationship between mechanical preparation of the root canal with nickel-titanium (NiTi) instruments and the formation of dentinal micro-cracks (4–8), which may potentially develop into vertical root fracture (9). It has been speculated that the design and the hard-hitting cutting ability of the preparation systems are the main reasons associated with the development of dentinal defects, because they might generate damaging forces toward dentin (10). Recently, a novel heat-treated NiTi system named TRUShape 3D Conforming Files (Dentsply Tulsa Dental Specialties, Tulsa, OK) has been introduced into the market, claiming to preserve more dentinal structure while providing an optimized canal debridement. The TRUSh- ape system uses the same symmetric triangular cross section but displays a proprietary file design that resembles an S-shape configuration, providing an ability to flex within the canal, creating an envelope of motion kinematics (11–13). Another system that is able to preserve more dentin is the Self-Adjusting File (SAF) (ReDent-Nova, Ra’anana, Israel). The SAF is a hollow file designed as a compressible cylinder composed of a thin NiTi lattice with an abrasive surface. It has the ability to adapt its shape to the root canal anatomy, applying a constant and delicate pressure on the canal walls, which might help to reduce the incidence of dentinal defects (4, 5). This system operates with a continuous flow of irrigant running through the instrument, allowing continuous replacement (8, 14, 15). From the *Department of Restorative Dentistry, Endodontic Division, Piracicaba Dental School, State University of Campinas, Piracicaba, S~ ao Paulo, Brazil; † Department of Endodontics, Fluminense Federal University, Niter oi, Rio de Janeiro, Brazil; ‡ Department of Endodontics, Grande Rio University, Duque de Caxias, Rio de Janeiro, Brazil; § Nuclear Engineering Program, Federal University of Rio de Janeiro, Rio de Janeiro, Rio de Janeiro, Brazil; jj Department of Dentistry II, Federal University of Maranh~ ao, S~ ao Lu  ıs, Maranh~ ao, Brazil; and ¶ Department of Restorative Dentistry, Dental School of Ribeir~ ao Preto, University of S~ ao Paulo, S~ ao Paulo, S~ ao Paulo, Brazil. Address requests for reprints to Prof Dr Gustavo De-Deus, Av. Henrique Dodsworth 85 Apto 808, Lagoa, Rio de Janeiro, RJ 22061-030, Brazil. E-mail address: endogus@gmail.com 0099-2399/$ - see front matter Copyright ª 2016 American Association of Endodontists. http://dx.doi.org/10.1016/j.joen.2016.11.013 Significance The TRUShape, Self-Adjusting File, BioRace, and Reciproc systems did not induce the formation of dentinal micro-cracks. Basic Research—Technology JOE — Volume 43, Number 4, April 2017 Frequency of Micro-cracks after TRUShape and SAF Preparation 619