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Assessment of mandibular ramus dimensions in relation to lower third molar impaction in class II malocclusion: a
Haya AbuHarb1,2, Bayan Abusafia3,4, Xuyuan Fu1
1Department of Orthodontics, Medical Center of Stomatology, The Second Xiangya Hospital, Central South University, Furong District, Changsha, Hunan, 410011, China.
Background:
To assess the relationship between mandibular ramus morphology and lower third molar impaction among patients with Class II malocclusion using CBCT.
Methods:
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.
Results:
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.
Conclusions:
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.
