Evaluation of mandibular ramus morphology using computed tomography in patients with mandibular prognathism and retrognathia: relevance to the sagittal split ramus osteotomy.

Purpose: The purpose of this study was to evaluate and compare the thickness of the mandibular ramus in patients with mandibular prognathism and retrognathia, as well as to assess the distribution of cancellous bone between the external and internal cortical plates above and posterior to the lingula.

Patients And Methods: The mandibular ramus of 40 patients, of whom 20 had prognathism and 20 had retrognathia, were evaluated by use of high-resolution computed tomography scanning.

Results: The mean thickness of the ramus in the prognathism group was 8.17 mm, which differed significantly from the mean value of 8.88 mm in those with retrognathia (P = .014). The mean vertical distance of the point of fusion between the cortical plates above the lingula was 8.95 mm for patients with prognathism and 9.41 mm for those with retrognathia, which was not a significant difference (P = .364). The mean horizontal distance of the point of fusion between the cortical plates posterior to the lingula was 8.32 mm for patients with prognathism and 9.74 mm for those with retrognathia, which was also not a significant difference (P = .066).

Conclusions: The mandibular ramus is thinner in patients with prognathism than in those with retrognathia. The distance of the point of fusion between the cortical plates above and posterior to the lingula is not influenced by the 2 types of mandibular deformity evaluated in this study. Computed tomography has proven to be a valuable tool to evaluate the morphology of the mandibular ramus.