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

IntroductionThe purpose of this study was to investigate the three-dimensional (3-D) morphology of isthmuses in the mesial roots of mandibular molars.MethodsOne 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 (Li) and the distance from the bottom of the isthmus to apex (Dba) were measured and analyzed.ResultsThe 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 Li and Dba in mandibular molars were 2.331 mm and 1.850 mm, respectively.ConclusionsMFMs present different anatomical features of isthmuses in the apical part of the mesial roots than MSMs.