Mechanism of transient mental nerve paraesthesia in sagittal split mandibular ramus osteotomy.

We investigated the mechanism involved in paraesthesia associated with sagittal split mandibular ramus osteotomy by three-dimensional computed tomography (3-D CT). Ten female patients underwent this procedure between 1988 and 1991. The inferior alveolar neuro-vascular bundles remained intact during the sagittal osteotomy in all cases. We examined the changes in the shape of the foramen mandibulae over a period of 6 months during which the transient mental nerve paraesthesia was recovered, and studied the distance from the foramen mandibulae to the spina mentalis (F-S distance) as measured on 3-D film. The postoperative 3-D CT scan showed bone resorption in front of the foramen mandibulae, and the F-S distance was shortened by an average of 2.94 mm. These findings suggest that possible causes of the paraesthesia is due to compression of the nerve trunk resulting from posterior movement of the mandibular ramus.