Three-dimensional Morphologic Analysis of Isthmuses in the Mesial Roots of Mandibular Molars

Introduction: The purpose of this study was to investigate the three-dimensional (3-D) morphology of isthmuses in the mesial roots of mandibular molars. Methods: One hundred twenty-six extracted mandibular molars including 70 first molars (MFMs) and 56 second molars (MSMs) from a Chinese population were scanned by micro computed tomography, and the apical 5 mm of the root canals with or without isthmuses was reconstructed with 3D-Doctor software. Each reconstructed isthmus model was assigned to 1 of the following 4 categories: sheet connection, separate, mix, and cannular connection. The length of the isthmus (L-i) and the distance from the bottom of the isthmus to apex (D-ba) were measured and analyzed. Results: The incidence of an isthmus in the apical 5 mm of the mesial roots was 85%. MFMs had more isthmuses with separate type and mixed type, whereas MSMs had more isthmuses with sheet connections. The L-i and D-ba in mandibular molars were 2.331 mm and 1.850 mm, respectively. Conclusions: MFMs present different anatomical features of isthmuses in the apical part of the mesial roots than MSMs. (J Endod 2010;36:1866-1869)