A simple method to locate mandibular foramen: preliminary radiological study.

INTRODUCTION

The position of mandibular foramen is variable at the medial aspect of mandibular ramus. Nevertheless its location is useful for the oral and maxillofacial surgeon in orthognatic surgery, especially in vertical ramus osteotomy (VRO) procedure. The aim of our study is to analyse the position of mandibular foramen in order to provide simple and reliable surgical landmarks.

MATERIALS AND METHODS

A radio-anatomical study was undertaken on normal mandibular panoramic X-ray examinations. Precise reproductions were outlined on tracing paper. Original orthonormal landmark was designed using posterior border of the ramus, mandibular incisure and anterior border of the ramus. All these elements are visible in the patient in VRO. Measurements of the position of mandibular foramen in horizontal and vertical dimensions were then performed with a ruler by two independent observers: l (width of mandibular branch), x (distance between posterior border of the ramus and mandibular foramen), h (height of mandibular branch) and y (distance between sigmoid notch and mandibular ramus). x/l and y/h ratios were calculated in order to minimise magnifications and image distortions due to the imaging process.

RESULTS

Forty-six panoramic X-rays were analysed, including 24 male and 22 female specimens (sex-ratio 1.1/1) with the mean-age 21 years. In vertical dimension, y/h ratio was distributed on a gaussian mode with a peak around 0.30-0.35, mandibular foramen was located around the midpoint of the inferior two-thirds and the superior third of the ramus, preferentially under this point. In horizontal dimension, x/l ratio observed the same model with a peak around 0.35; mandibular foramen was located around the midpoint of the anterior two-thirds and the posterior third of the ramus, preferentially in front of this point. Mandibular foramen was situated in the ventral and inferior two-thirds of the ramus without difference according to the side, sex or age.

DISCUSSION

Posterior and superior thirds of the ramus constitute a "safety zone" where mandibular foramen is unlikely to be found. This area can be used by the oral and maxillofacial surgeon in vertical ramus osteotomy of the mandible with low inferior alveolar nerve morbidity probability.