Distraction osteogenesis after membranous bone onlay grafting in a dog model

Purpose: The purpose of this experiment was to study the possibility of dis traction osteogenesis in a membranous bone onlay graft to the mandible and to clarify the histology of the bone repair. Materials and Methods: Four dogs, 5 months of age at the beginning of the e xperiment, were used for this study. The zygomatic arch was exposed in the subperiosteal plane, and a 3-cm long, full-thickness portion of the arch wa s harvested. The lateral surface of the mandibular body was exposed in the subperiosteal plane, and the bone was fixed to the lateral surface as a mem branous onlay graft using screws. A vertical osteotomy through the graft an d underlying mandibular body was done postoperatively at week I in dog 1, w eek 2 in dog 2, week 3 in dog 3, and week 4 in dog 4. An external distracti on device was applied to the mandibular body, and distraction was started 7 days after the operation at a rate of I mm/d for 10 days. After completion of distraction, the device was left in place for 6 weeks to allow for bony consolidation. Radiographs were carried out at 2, 4, and 6 weeks postdistr action. All dogs were killed 6 weeks after distraction. Results: New bone between the native underlying mandibular segments was gen erated in the distraction zone in all dogs. New bone was not generated betw een the segments of the membranous bone onlay graft in dog 1, but was gener ated in dog 2, dog 3, and dog 4. However, in dogs 2 and 3, the new bone bet ween the segments was less firm, with more fibrous tissue, than the bone be tween the native underlying mandibular segments. Histologically, the distra ction gap between the segments of the membranous bone onlay graft in dogs 2 and 3 was composed of considerable fibrous tissue in the central zone and activated osteoblastic cells forming new bone in the margins. In dog 4, the re was much more osteoblastic activity in the distraction gap, and the new bone had the appearance of almost normal cortical bone. Conclusion: These findings show that distraction osteogenesis is possible i n a membranous bone onlay graft and suggest that the distraction should be performed at least 4 weeks after the onlay grafting. (C) 2001 American Asso ciation of Oral and Maxillofacial Surgeons.