CBCT Analysis of the Position and Course of the Mandibular Canal in Prognathism

Objective: The aim of this study was to investigate the position and course of mandibular canal in mandibular prognathism with cone-beam computerized tomography(CBCT),and to relate the findings of sagittal split ramus osteotomy,and also describe the anatomical variations of mandibular canal in order to reduce injuries to the inferior alveolar nerve.Methods: 28 patients with skeletal Class Ⅲ mandibular prognathism(10 males and 18 females) were examined by CBCT.The position and course of mandibular canal from the lowest point of mandibular foramen to the first molar were measured at five specific landmarks.5 sections from the mandibular foramen to the mandibular first molar area were analyzed,including inner and outer diameter,mandibular bone thickness and the distance between mandibular canal and the buccal and lingual bone cortex,and the inferior border of mandible bone.Statistical analysis was performed using the SPSS 17.0 software package.Results:Mandibular bone became thicker gradually from the mandibular ramus to the forepart of the mandibular angle,and thinner forward to the position where the mandibular first molar projected on the mandibular bone.Cortical bone of buccal side of the mandibular ramus became thicker forward to the mandibular angle and thinner to the mandibular body.At each section,the bone marrow cavity in the buccal side was always lager than in the lingual side.Width difference between left and right side of lingual bone marrow cavity were statistically significant.The width of buccal bone marrow cavity,thickness and inner and outer diameter of mandibular bone were statistically different between genders.Three types of connections between mandibular canal and buccal bone cortex were demonstrated in CBCT: 92.5% of which were separate type,6.07% were contact type,and 1.43% were fusion type.Conclusion:This work demonstrates that CBCT can accurately locate the mandibular canal and anatomic structures,which can provide guidance to the design of sagittal split ramus osteotomy for patients with mandibular protrusion.