ORIGINAL RESEARCH Shaping ability of two root canal instrumentation systems in oval-shaped canals: A microcomputed tomography study Suelen Recepute Xavier, MSc 1 ; Carolina Oliveira de Lima, MSc 2 ; Marı ´lia Fagury Videira Marceliano-Alves, PhD 3 ; Mariane Floriano Lopes Santos Lacerda, PhD 4 ; Ricardo Tadeu Lopes, PhD 5 ; and Celso Neiva Campos, PhD 1 1 Department of Dental Clinic, Federal University of Juiz de Fora, Juiz de Fora, MG, Brazil 2 Departament of Endodontics, State University of Rio de Janeiro, Rio de Janeiro, RJ, Brazil 3 Department of Dentistry Research, Iguac ¸ u University, Nova Iguac ¸ u, RJ, Brazil 4 Department of Dentistry, Federal University of Juiz de Fora, Governador Valadares, MG, Brazil 5 Nuclear Engineering Program, University of Rio de Janeiro, Rio de Janeiro, RJ, Brazil Keywords Canine tooth, endodontic instrument, endodontics, root canal preparation, X-ray microtomography. Correspondence Carolina Oliveira de Lima, Rua Rog ´ erio Karp, 310/104, 22795-216 Recreio dos Bandeirantes, Rio de Janeiro, RJ, Brazil. email: c.oliveiradelima@yahoo.com.br doi: 10.1111/aej.12469 (Accepted for publication 8 November 2020.) Abstract The objective was to evaluate the shaping ability of XP-endo Shaper and Mtwo systems in oval-shaped canals preparation by microcomputed tomography (micro-CT) along the entire canal. The volume, surface area and percentage of unprepared area were evaluated by image processing in entire canal and apical third (5 mm). Apical transportation and centring ability were evaluated at 3, 5 and 7 mm from the apex. Forty single-canal oval canines were paired in two groups (n = 20) according to the instrumentation system: XP-endo Shaper and Mtwo. The teeth were scanned by micro-CT before and after instrumentation, using a thermal vat at 37°C. The XP-endo Shaper system was more effective in the instrumentation of oval-shaped canals when compared to Mtwo system, resulting in greater volume increases and lower percentage of unprepared canals walls in apical region. Regarding apical transportation and centring abil- ity, no statistical difference was observed. Introduction Successful endodontic treatment depends on root canal system cleaning and shaping (1). However, motor-driven instruments used during mechanical preparation are not completely effective in cleaning oval-shaped canals as they tend to remain in the centre of the canal and ade- quate buccolingual dimension preparation is not achieved (2). The presence of such non-instrumented areas, regardless of instrumentation technique or applied instrument, allows for the accumulation of pulp rem- nants and persistent microorganisms, which may lead to unsuccessful endodontic treatment (1,2). The root canal morphology of mandibular canines is complex and displays a highly variable internal canal configuration (3,4). According to Wu et al. (3), mandibu- lar canines display a high incidence of oval-shaped canals and this anatomical configuration posing a significant challenge for adequate root canal treatment, leaves some untouched areas in the root canal, favouring the accumulation of debris and microorganisms (5,6). There- fore, endodontic instruments have undergone various modifications in their design and heat treatments of their alloys trying to allow better root canal preparation and to maintain the original canal shape. Mtwo is a well-known rotary system (VDW, Munich, Germany), which comprises an “S” cross-sectional design and an inactive safety tip. It is, therefore, characterised by a positive inclination angle with two cutting edges, effective in cutting dentin. This favours helical root canal residue removal, which present sinuous profile walls (7). XP-endo Shaper (FKG Dentaire, La Chaux-de-Fonds, Switzerland) is a system made of MaxWire ® alloy that improves superelasticity and shape memory, in addition is able to react to temperature variations and adapt itself to the canal morphology, due to expansion and contrac- tion capacity (8,9). This instrument presents a 30/.01 diameter and is able to reach a final preparation compati- ble with a 30/.04 instrument when in contact with body temperature (10). © 2020 Australian Society of Endodontology Inc 1 Aust Endod J 2020