radicular anatomy of permanent mandibular second molars in an iranian population: a preliminary study

background: root morphology is of utmost importance to endodontic sciences. since there are a few studies on the morphology of mandibular second molars’ roots, and some anatomical variables are not evaluated before, the aim of this study was to investigate thoroughly radicular anatomy of this tooth. materials and methods: this ex vivo study was performed on 150 intact mandibular second molars. after access cavity preparation and ensuring canal patency, indian ink was injected into root canals from the orifices. the teeth became transparent using methyl salicylate storage. then, they were inspected by an endodontist under a ×10 stereomicroscope regarding numerous root morphological variables. data were analyzed using chi‑square test and analysis of variance (α = 0.05). results: about 86.7% of teeth had two roots and 13.3% were single‑rooted ( p = 0.0001), of which, 50% were c‑shaped (6.7% of all teeth, p = 0.0001). 86.7% of mesial roots were double canalled, whereas 75.3% of distal roots were single canalled ( p = 0.0001). 71.45% and 95.3% of the mesial and distal roots had one apical foramen, respectively ( p = 0.0001). apical foramens were mostly central followed by lingual in most cases. distances between apical foramen and apical constriction ranged between 0.27 and 0.40 mm ( p = 0.0545). distances between apical foramen and root apices ranged between 0.30 and 0.47 mm ( p = 0.0001). vertucci classifications of mesial canals were type ii in 62.6% and type iv in 37.4%. 86.2% of single‑canal distal roots were type i. 66.7% of double‑canal distal roots were type ii and 33.3% were type iv ( p = 0.0001). the mean root lengths from cervical to apex of mesial, distal, and single roots were 14.02 ± 0.85 (95% confidence interval [ci] = 13.87–14.17), 13.35 ± 0.91 (95% ci = 13.19–13.50), and 14.25 ± 0.72 mm (95% ci = 13.91–14.58), respectively. the extents of canal curvatures varied between 20° and 31° buccolingually ( p = 0.0000), and between 19° and 27° mesiodistally ( p = 0.0000). conclusion: there was a considerable rate of eccentric apical foramen in mandibular second molars. key words: anatomy, apical, constriction, apical foramen mandibular, second, molar, root, curvature