ORIGINAL RESEARCH Mandibular canines with additional roots: An ex vivo study of the external and internal morphology Panagiotis Beltes, DDS, PhD 1 ; Eleni Kantilieraki, DDS 1 ; Maria-Elpida Kalaitzoglou, DDS 1 ; Charalampos Beltes, DDS, MSc, MClinDent, PhD 1 ; and Christos Angelopoulos, DDS, MSc, PhD 2 1 Department of Endodontology, School of Dentistry, Aristotle University of Thessaloniki, Thessaloniki, Greece 2 Department of Dentoalveolar Surgery, Implantology and Radiology, School of Dentistry, Aristotle University of Thessaloniki, Thessaloniki, Greece Keywords cone beam computed tomography, external morphology, internal morphology, three- rooted mandibular canines, two-rooted mandibular canines. Correspondence Professor Panagiotis Beltes, Department of Endodontology, School of Dentistry, Aristotle University of Thessaloniki, Agiou Dimitriou Str 54124 Thessaloniki, Greece. Email: beltes@otenet.gr doi: 10.1111/aej.12305 (Accepted for publication 31 July 2018.) All authors have contributed significantly to all aspects of this study and are in agreement with the present manuscript. Abstract The aim of this study was to investigate the root and root canal morphologies of mandibular canines with additional roots using cone-beam computed tomography. Seventy-seven extracted two-rooted and one-three-rooted per- manent human mandibular canines were selected. Aspects of the external morphology evaluated were crown length, root length, total length, root bifur- cation distance from the cementoenamel junction, root size, and direction of the root curvature in the apical third. Features of internal morphology assessed were root canal number per root, root canal bifurcation distance from the cementoenamel junction, and the angle between the buccal or lingual canal and the main canal. The root size and length presented considerable diversity. Most of the roots bifurcated at the middle third and exhibited a buccal curva- ture. The main root canal bifurcated coronally in two root canals, a buccal and a lingual. The majority of the buccal and lingual root canal angles were blunt. The presence of a third root in a specimen was a novel finding of this study. Introduction In order to ensure the highest possible success rate of endodontic treatment, the clinician should be aware of the morphological features of all teeth and their possible variations (1,2). Mandibular canines usually have one root and one root canal (3,4). The reported prevalence of a second canal varies between 1.2% (3) and 28.2% (5), while a second root has been reported to be present in 0.3% (6) to 12.1% (7) of cases. Although many scientific papers concerning the number and type of root canals in mandibular canines have been published, there is little detailed information available regarding the external and internal morphologies of two-rooted mandibular canines. Only two studies have exclusively investigated the morphology of two-rooted mandibular canines. Sharma et al. (8) examined 65 extracted two-rooted mandibular canines utilising a canal staining and tooth clearing tech- nique. Their study provided size and length measure- ments of the roots, recordings of the different root curvatures, and the number of root canals per root for the first time in the literature. Versiani et al. (9) studied 14 extracted two-rooted mandibular canines with the aid of micro-computed tomography (micro-CT). This tech- nique allowed for further measurements of these teeth, focusing on volumetric and area data of for the root and root canal. The aim of the present study was to investigate the external and internal morphologies of mandibular cani- nes with additional roots, noting aspects of major clinical significance, using cone-beam computed tomography (CBCT). Materials and methods The study protocol was approved by the Research Com- mittee of the Aristotle University of Thessaloniki, Greece (protocol no.28/03-02-2016). Seventy-seven two-rooted and one three-rooted unre- stored permanent human mandibular canines with fully formed apices were collected in the Undergraduate Department of the School of Dentistry, Aristotle © 2018 Australian Society of Endodontology Inc 1 Aust Endod J 2018