Characterizations of three-dimensional root morphology and topological location of mandibular third molars by cone-beam computed tomography

Purpose This study aimed to delineate three-dimensional (3D) root morphology and topological locations of mandibular third molars (MTMs) by cone-beam computed tomography (CBCT) in a Chinese adult dental population. Methods Adult patients with MTMs were retrospectively screened based on CBCT images at our institution between January 2018 and December 2019. Root morphology and spatial locations of these teeth were defined based on CBCT 3D images. Potential associations with epidemiological and clinical/radiological parameters were analyzed using Chi-square or Fisher exact test. Two-tailed P values less than 0.05 were considered statistically significant. Results A total number of 2680 eligible patients (male/female:0.74; 35 ± 10 years old) with 4180 MTMs were enrolled. The majority of MTMs had 2 roots 3064 (73.30%), followed by 800 (19.14%) 1 root, 302 (7.22%) 3 roots, and 14 (0.33%) 4 roots. More than half of one-rooted MTMs were convergent, followed by club-shaped and C-shaped. Among MTMs with 2 roots, 2860 (93.34%) were M–D (mesio-distal) types. Most MTMs with 3 roots were M–2D (one root in mesial, two roots in distal) types, followed by 2M–D (two roots in mesial, one root in distal) types, and B–2L (one root in buccal, two roots in lingual) types. The presence of root configurations was significantly associated with the angulation, depth, and width classification in two-rooted MTMs ( P < 0.05). Conclusions Although the morphology and spatial locations of MTMs vary greatly, our results from a large dental population reconfirm that most MTMs have two roots with mesial–distal type of spatial distribution.