CBCT assessment of inferior alveolar canal and surrounding bone morphology in long and short hemimandibles across mandibular asymmetry severity

This study aimed to compare inferior alveolar canal and surrounding bone morphology between the long and short hemimandibles at three anatomical levels relevant to bilateral sagittal split osteotomy (BSSO) and to determine whether bilateral morphometric differences vary according to the severity of mandibular asymmetry. Preoperative cone-beam computed tomography images of 57 adults (19–42 years; 28 women and 29 men) were retrospectively evaluated. Participants were classified according to Menton deviation as symmetric (≤ 2 mm; n = 20), mild asymmetry (> 2 to ≤ 4 mm; n = 18), or severe asymmetry (> 4 mm; n = 19). Eighteen morphometric parameters were measured bilaterally at the mandibular foramen entry, ramus–body transition, and second molar levels. Long and short hemimandibles were compared within each group, and short−long differences were compared among groups. Benjamini–Hochberg false discovery rate correction was applied for multiple comparisons. After false discovery rate correction, no significant bilateral differences were observed in the symmetric group, whereas 7 parameters differed significantly in the mild asymmetry group and 10 in the severe asymmetry group. Seven short−long differences varied significantly among the three groups. Four parameters—buccal cancellous bone thickness and canal diameter at the ramus–body transition, and canal–alveolar crest distance and buccal cancellous bone thickness at the second molar level—showed a stepwise increase from symmetric to mild and severe asymmetry. Bilateral differences in inferior alveolar canal and surrounding bone morphology became more pronounced with increasing mandibular asymmetry, particularly in cancellous bone at BSSO-relevant anatomical levels. Side-specific assessment of the inferior alveolar canal and surrounding bone may provide additional anatomical information for BSSO planning in patients with mandibular asymmetry.