Acceleration Osteogenesis And Maturity Of The Distracted Callus

Distraction osteogenesis(DO) in the treatment of congenital and acquired craniomaxillofacial deformities has been an alternative and widely used. Comparing to the conventional orthognathic surgery techniques,DO is less invasive and eliminates the need for a donor site operation.In addition, simultaneous expansion may improve long-term stability.Although numberous experiments and clinical studies on DO appeared,there are still some questions unclear,including long duration of treatment and incidence of complications. Attempts should be made to accelerate osteogenesis and promote maturity of the distracted callus.Based on these questions,we did some works as follows: Part I Study on Distraction Osteogenesis in the Irradiated Rabbit Mandible1. Experimental model of distraction osteogenesis in the irradiated rabbit mandibleThe potential use of distraction osteogenesis in mandibular reconstruction has been limited by its questionable efficacy in previously radiated bone. We designed a rabbit model,in which the rabbits underwent a total dose of 27.0 Gy of external beam 6 MeV irradiation with a standard linear accelerator in five 5.4 Gy fractions within a 10-day period,which is biologically equivalent to 50 Gy in 25 fractions. Bilateral osteotomy was made 3 months after completion of radiotherapy.A distractor was placed which is designd to be fixed subcutaneously and allows simultaneous bilateral distraction of the body of the mandible. Results showed that by using the distractor, we could effectively lengthen rabbits's mandible and the distractor fixed well. The rabbits tolerated the irradiation,surgical procedure and the distraction period well.No immediate radiation side effects happened in our study.The rabbits did not show impairment of mastication during the entire experiment period. Osteodistraction resulted in protrusion of the mandible and crossbite.So the rabbit model was suitable for study of mandibular osteodistraction.2. Distraction osteogenesis in the irradiated rabbit mandibleThe purpose of this study was to evaluate the effects of irradiation on mandibular distraction osteogenesis. Six rabbits received a unilateral irradiation (group RA) in the mandible with a total dose of 27.0 Gy in five 5.4 Gy fractions.The contralateral side served as control (group NO).Bilateral osteotomy was made 3 months after completion of radiotherapy. After a 1 week latency period bone distraction was activated at a rate of 0.5 mm twice daily for 10 days, followed by a consolidation phase of 6 weeks. Amount of new bone was measured histomorphometrically. Portion of new bone area and BMD was equal in all groups. Bone was more mature and bone spicules better organized in group NO than in groups RA. Cartilaginous cells were found larger in distracted bone of group RA than group NO. It seems that despite delayed bone formation, DO can be performed after radiotherapy.3. Effect of recombinant basic fibroblast growth factor on distraction osteogenesis of irradiated rabbit mandibleThe possible osteogenetic effect of recombinant human basic fibroblast growth factor (bFGF) on lengthening of irradiated mandibles was investigated in the rabbit. Rabbits underwent bilaterally external beam irradiation in the mandible with a total dose of 27.0 Gy in five 5.4 Gy fractions.Three months after completion of radiotherapy, bilateral mandible distraction osteotomy was performed followed by bone lengthening of the mandible using an intraoral device at a rate of 0.5 mm twice daily for 10 days. 10 ug bFGF in 0.3 ml fibrin glue was injected into the regenerate bone of either hemimandible on the same day after completion the distraction.In the contralateral side,0.3 ml fibrin glue without bFGF was injected. Rabbits were sacrificed at 2, 4 and 6 weeks after completion of bone lengthening. Radiographic evaluation indicated a significant increase in bony union of the distraction regenerate in the bFGF treated groups compared with the control groups.Corresponding to the radiographic findings, the histological examination show...