CASE REPORT/CLINICAL TECHNIQUES C-shaped Canal System in Mandibular Second Molars: Part I—Anatomical Features Bing Fan, DDS, MS, PhD, Gary S.P. Cheung, BDS, MDS, MSc, Mingwen Fan, DDS, James L. Gutmann, DDS, PhD, FACD, FICD, FADI, and Zhuan Bian, DDS, MS, PhD The purpose of this study was to investigate the anatomical features of C-shaped root canal system in mandibular second molars using micro-computed tomography (CT). Fifty-eight extracted mandibular second molars with fused roots were collected from a native Chinese population. The teeth were scanned into layers of 0.5-mm thickness by CT and mea- surements were made at eleven levels. The ratio of the depth of the deepest part of the groove to the buccal-lingual thickness of the cross-section of the root was calculated for each tooth. The canal shapes of the scanned cross-sections were assessed and classified according to a modified Melton’s method. Results were subject to the Kruskal-Wallis test. Of the 58 molars, 54 had a C-shaped canal system with a mean groove-to-thickness ratio of 47.96%; the four teeth without a C-shaped canal had a mean ratio of 14.82%. Most orifices (98.1%) were found within 3 mm below the cementoenamel junction. Of teeth with a C-shape canal system, a majority demon- strated an orifice with an uninterrupted “C” configu- ration. Seventeen canals divided in the apical portion, most of which did so within 2 mm from the apex. The cross-sectional shape varied drastically along the length of the canal. Teeth with a high groove-to- thickness ratio had at least one section with C1, C2, or C3 configuration. The canal shape in middle and apical thirds of C-shaped canal systems could not be predicted on the basis of the shape at the orifice level. Section 2 of this paper addressed the correla- tion between the radiographic appearance and these CT images. The C-shaped canal system is an anatomical variation mostly seen in mandibular second molars, although it can also occur in maxillary and other mandibular molars (1, 2). The main anatomical feature of C-shaped canals is the presence of a fin or web connecting the individual root canals—the orifice may appear as a single ribbon- shaped opening with a 180° arc linking the two main canals (3). Typically, this canal configuration is found in teeth with fusion of roots either on its buccal or lingual aspect. In such teeth, the floor of the pulp chamber is usually situated deeply and may assume an unusual anatomical appearance. A number of reports have described different trends in the shape and number of roots and root canals among different human races (3, 4). The variation appears to be genetically determined and may be used in tracing the ethnic origin of the subjects (3). The prevalence of C-shaped canal system in second mandibular molars has been reported to be 31.5% for the Chinese population (5), which is much higher than that reported for other populations (1, 4). When present on one side, a C-shaped canal may be found in the contralateral tooth in over 70% of individuals (6). Roots containing a C-shaped canal often have a conical or square configuration (7, 8). The description regarding these roots was identified initially in comparative anthropology. Manning (7) speculated that the failure of the Hertwig’s epithelial root sheath to fuse on the lingual or buccal root surface was the main cause of a C-shaped root, which always contains a C-shaped canal. The C-shaped root may also be formed by coalescence because of deposition of cementum with time (7). The C-shaped canal system can assume many variations in its configuration. Melton and co-workers (9) proposed a classification of C-shaped canals based on their cross-sectional shape. However, it has been pointed out that this shape can vary along the length of the root so that the clinical crown morphology or the appearance of the canal orifice may not be good predictors of the actual canal anatomy (10). In Melton’s classification, there has been no clear description of the difference between categories II and III (i.e. C2 and C3, respectively, in Fig. 1), as well as the clinical significance. Furthermore, they examined three arbitrary levels of the root and hence little information is present describing how the canal shape may change over its length. Cooke and Cox (1) were first to describe the clinical significance of C-shaped canals, which present a challenge with respect to their debridement and obtura- tion. This is especially true when it is uncertain whether a C-shaped orifice found on the floor of the pulp chamber may continue to the apical third of the root. Irregular areas in a C-shaped root canal JOURNAL OF ENDODONTICS Printed in U.S.A. Copyright © 2004 by The American Association of Endodontists VOL. 30, NO. 12, DECEMBER 2004 899