Changes in the inferior alveolar nerve after mandibular lengthening with different rates of distraction

Purpose: This study investigated the changes in the inferior alveolar nerve after mandibular lengthening with different rates of distraction. Materials and Methods: Bilateral mandibular corticotomies were performed in 8 goats. The mandibles in 6 goats were lengthened 10 min using a custom-made distractor with 2 different rates of distraction (1 mm/d [n = 3] and 2 mm/d [n = 3]); the other 2 nondistracted mandibles served as a control. The goats with distracted mandibles were killed at 2 weeks after completion of distraction. The inferior alveolar nerve specimens from all animals were harvested and processed for histologic and ultrastructural evaluation. Results: The mandibles were lengthened successfully in the distracted animals. Morphologic changes in the inferior alveolar nerves were observed when compared with the nondistracted controls. Moreover, signs of nerve degeneration, such as demyelination, axonal swelling, axoplasmic darking, and decrease in the number of axons, were more extensive and prominent in those nerves distracted at a rate of 2 mm/d. Conclusions: Degenerative changes in the inferior alveolar nerve occur after mandibular lengthening by distraction osteogenesis. The distraction rate of 1 mm/d appears to be tolerable and safe for the inferior alveolar nerve, but rapid distraction may cause serious degeneration. (C) 2001 American Association of Oral and Maxillofacial Surgeons.