The purpose of this study is to determine the 3-dimensional location of mandibular canal (MC), thickness of the cortical and cancellous bone at distal of 1^st and 2^nd mandibular molars in patients with Class 3 dentofacial deformity and compare with the dentoskeletal Class I individuals in relevance to sagittal split ramus osteotomy.

The study was conducted on CBCT images of 30 dentoskeletal Class I patients with a mean age of 22.9 years and 30 dentoskeletal Class III patients with a mean age of 21.27years.

The comparison of the measurements in the distal root of the first molar area showed that: thickness of the buccal cancellous bone, the distance from buccal aspect of MC to outer buccal cortical margin of mandible and the distance between superior aspect of MC and alveolar crest were significantly greater in Class I patients. The comparison of the measurements in the distal root of the second molar area showed that; the distance between superior aspect of MC and alveolar crest was significantly greater in Class I patients. However, the distances from the distal margin of mental foramen was significantly lower in Class I patients (P<0.05).

In case of deviated skeletal development, position and size of anatomical structures can vary significantly. Prognathic mandibles has increased risk of neurovascular complications and bad splits. Morphologic data provided in this study may help practitioners for better surgical planning to reduce complications.