Histological changes and expression of nerve growth factor in the inferior alveolar nerve after distraction osteogenesis

Park, Bong Wook; Kim, Jong Ryoul; Byun, June Ho

Abstract

Distraction osteogenesis (DO) is frequently used technique in reconstruction of bony defects resulted from tumor resection, congenital deformity, and trauma in the maxillofacial region. Although the histologic and ultrastructural changes associated with distraction osteogenesis have been extensively described, the exact changing of the surrounding tissues, such as nerve tissues, were still unclear. This study observed the histological changes and the expression of nerve growth factor (NGF) in the inferior alveolar nerve (IAN) after distraction osteogenesis. Unilateral mandibular distraction (0.5 mm twice per day for 10 days) was performed in eight mongrel dogs. Two animals were sacrificed at 7, 14, 28 and 56 days after completion of distraction, respectively. The distracted IAN and contralateral control nerve were harvested and processed for histological and innunohistochemical examinations. The signs of acute nerve injuries, such as demyelination and partial discontinuation of nerver fiber, were observed in the distracted IAN on 7 and 14 days after distraction. The initial remyelination and regeneration of distracted IAN were showed at 14 days after completion of distraction. At 56 days later, the histologic features of distracted IAN was similar to those of the normal control IAN. The expression of NGF was significantly increased in most distracted nerve tissues on 7, 14 and 28 days after distraction. On 56 days after distraction, the expression of NGF returned to the normal level. This study suggested that the acute IAN injury caused by mandibular distraction were mostly recovered during consolidation period. The NGF was seemed to be induced from Schwann cell and damaged nerve tissues, and it may have important roles in the initial healing of damaged nerves.