| Distraction osteogenesis (DO), that is bone lengthening following an osteotomy and a latency period, was originally introduced by a Russian orthopaedic surgeon Ilizarov, who also defined the main principles used nowadays in DO. The basic principles of DO were originally defined for long bones, but have successfully been used also in craniofacial bones. The use of DO in the treatment of congenital and acquired mandibular deformities has increased significantly. But the osteogenesis mechanism in mandibular DO has not been fully understood. For human sample is unavailable, it is important to establish a proper animal model of mandibular DO. Some authors have reported DO models, but each had its lacks and shortcomings. The present study tried to make an improvement in the animal model of mandibular DO repair the bone defect.Twenty-five adult healthy rabbits were used in this study and divided into six groups by random. (1) Five groups were experimental groups, and four rabbits in each group. Unilateral mandibular osteotomy was performed on twenty rabbits. By operation, a self-made distraction device was implanted. After a 6-day latency, therabbits underwent distraction for 8 days and entered into the consolidation period. There was a distraction phase of 8 days, during which gradual distraction was performed at a rate of 0.4mm every 12h, and a consolidation phase, during which the internal distractor remained in place with no distraction. Four rabbits were respectively killed at different time points (4 days, 8days after distraction and 2 weeks, 4 weeks, 6 weeks after consolidation). (2) One group was experimental control group. Five rabbits of experimental control group were performed the same osteoctomy as experimental groups and not performed the distraction after osteotomy. One animal was respectively killed at corresponding time in experimental groups. (3) A block of normal bone come from a rabbit of experimental groups was used as empty control.Major steps of the operation: Following general and local anesthesia, an about 3 to 4cm longitudinal incision was made on the lateral aspect of unilateral mandible, and after the muscles had been separated, the mandible was exposed. A block of bone about 6.4mm width was cut off and formed a mandibular bone defect. Six pins were inserted into the mandible in order to fixed the distractor and then an osteotomy was made gently between the second and third pins. After this procedure, the wound was washed and closed.All the procedures used in this study have been well tolerated by twenty-five rabbits. There were no appearent wound infection. The distraction devices were stable and produced well and maintained the distraction amount required. The distraction gaps were filled with regenerated bone tissue. The mandibular bone defects were repaired successfully. The method in this study is practicable and repeatable which could be used to establish an animal model of mandibular distraction osteogenesis in rabbits.The distracted bone tissues were dissected with the surrounding soft tissues and fixed overnight. The samples were then decalcified with 10% ethylene-diaminetetraacetate (EDTA), and then embedded in paraffin according to the standard procedure. Finally sections of 4.0-um thickness were cut on a microtome and mounted on slide glasses and stained with hematoxylin & eosin. The expression of c-fos, OPG and OPGL were detected by ultrasensitive S-P immunohistochemical method.Histological examinations showed that distraction zone of 4 days, 8days after distraction were filled with fibril connective tissues in which had a lot of fibroblasts. The osteotomized bone edges were surrounded by a small amount newly formed trabecular bone. Adjacent to them a large number of osteoblasts were observed, and occasionally, a few chondrocytes in cortical bone islands could be seen. Endochondrai ossification was seen between the osteotomy sites at this stage of distraction. The distraction zone of 2 weeks, 4 weeks after consolidation, there were numerous newly formed bones at both sides of the ce...
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