Anatomic study to determine a safe surgical reference point for mandibular ramus osteotomy

Abstract

OBJECTIVE: The purpose of this study was to identify a surgical reference point on the mandibular ramus that can be used during ramus osteotomy to prevent injury to the inferior alveolar nerve. MATERIALS AND METHODS: A total of 125 subjects' mandibles were analyzed and compared on a three-dimensional (3D) model constructed from computed tomography (CT). 25 volunteer subjects with normal class I occlusion (group I, control), 50 consecutive subjects (25 females and 25 males) diagnosed with mandibular retrognathism (group II), and 50 consecutive subjects (25 females and 25 males) with prognathism (group III) were included. This study created a landmark (the midwaist point) at the halfway point on a horizontal plane between the most concave points on the anterior and posterior borders of mandibular ramus, with the vertical plane bisecting the horizontal plane. The midwaist point was compared to other anatomic landmarks including antilingula, lingula, and mandibular foramen for correlation. RESULTS: The distance from the midwaist point to lingula and mandibular foramen along the horizontal plane was not significantly different among three groups. Lingula and mandibular foramen were mostly located within 2 mm posterior of the midwaist point, whereas the locations of lingula and mandibular foramen along the vertical plane to the midwaist point were highly variable. CONCLUSION: The midwaist point is an excellent intraoperative reference point that can help surgeons to identify the position of the lingual and the mandibular foramen, thus preventing inferior alveolar nerve injury.