[Measurement of the mandibular ramus in prognathism with computed tomography]

The aim of this study is to investigate the morphology of the mandibular ramus at lingual plane using spiral computed tomography and compared with the control patients.

The mandibles from 35 patients with skeletal Class III prognathism undergoing sagittal split ramus osteotomy and 20 control patients without dentofacial deformity were evaluated on spiral computed tomography. The thickness of the mandible, diameter of the inner mandibular canal, width of the bone marrow space between the outer wall of the mandibular canal and the buccal cortex, and the width of the buccal cortex and lingual cortex was measured at lingual plane. All measurements were analyzed with SPSS 13.0 software package. Differences between groups were tested for statistical significance using Student's t test.

The thickness of the mandible was 8.42 mm in prognathic patients,and 9.65 mm in control patients.The width of the bone marrow space at the buccal side in prognathic patients was 1.58 mm,and 2.39 mm in control patients. There was a significant difference between the two groups in the total thickness of the mandible (t= -4.612, P<0.001).This trend was also found in the bone marrow space between the outer mandibular canal and the inner surface of the buccal cortical bone(t= -5.434, P<0.001).

Compared with the control patients ,the mandibular ramus of the skeletal Class III is thinner, and the width of the bone marrow space between the outer wall of the mandibular canal and the buccal cortex is smaller.