Root Canal Morphology of Permanent Three-rooted Mandibular First Molars-Part I: Pulp Floor and Root Canal System

Introduction: Racial variations in root form and canal anatomy present endodontic challenges for clinicians. This study examined root canal morphology of three-rooted mandibular first molars by micro computed tomography scans. Methods: A total of 122 extracted mandibular first molars were collected from a native Chinese population. After calculating the frequency of occurrence, 20 three-rooted (experimental group) and 25 two-rooted first molars (control group) were scanned and reconstructed three-dimensionally. Results: The frequency of three-rooted mandibular first molars was 31.97% (39/122). The mean interorifice distances from the distolingual (DL) canal to the distobuccal (DB) and mesiolingual canal were 2.93 mm and 2.86 mm, respectively. The mesial root predominately contained a type 2-2 root canal, with an incidence of 65% in the experimental group and 64% in the control group. Type 1-1 canals were seen more frequently in the DL and DB roots of the three-rooted first molars as well as in the distal roots of the two-rooted first molars. The incidences were 100% (20/20), 95% (19/20), and 72% (18/25), respectively. Accessory and lateral canals rarely occurred in the extra DL roots. The incidence was only 10% (2/20). A furcation canal extending from the floor to the furcation region was not observed. Conclusion: Three-rooted mandibular first molars commonly have 4 separate canals with high incidences of accessory canals in the mesial and DB root. The geometric data of pulp floors are useful for locating the extra DL canal. (J Endod 2010;36:990-994)