Assessment of mandibular ramus dimensions in relation to lower third molar impaction in class II malocclusion: a comparative 2D and 3D CBCT evaluation

To assess the relationship between mandibular ramus morphology and lower third molar impaction among patients with Class II malocclusion using CBCT.

A retrospective study included 536 patients with Class II malocclusion, classified into normally erupted (n = 84), impacted (n = 359), and absent third molar groups (n = 93). Mandibular ramus dimensions, including height, widths, condyle to gonion length, retromolar space, coronoid process length, and gonial angle, were measured using CBCT-derived 2D and 3D images. Third molar impaction was classified using the Pell&Gregory and Winter systems.

The third molar position differed significantly between groups across Pell and Gregory, ABC, and Winter classifications, with P = 0.0001. Impacted molars were mainly Class II or III, position C, and mesioangular or horizontal (57.1%, 32.9%, 52.44%, 46.2%, 36.5%, respectively). Gender distribution showed no significant difference. Retromolar space was significantly reduced in the mean value in the impacted group at 5.77 ± 2.63 mm compared with the normal group at 14.49 ± 3.79 mm and the without-molar group at 13.95 ± 2.90 mm. Condyle to gonion length and ramus height showed no significant differences in 2D or 3D sagittal measurements but were significantly reduced in the impacted group on 3D volumetric analysis with P = 0.022 and P = 0.002. Maximum ramus width differed significantly across groups. Significant differences were observed between 2D and 3D measurement methods.

Third molar impaction in Class II patients is mainly associated with reduced retromolar space and subtle mandibular volumetric deficiencies. 3D CBCT offers a more comprehensive assessment than 2D imaging, while linear and angular parameters show minimal clinical relevance.