Study On Reconstruction Of Rabbits' Mandibular Traumatic Defects By DO Technique

Maxillofacial regions are often under attack whether in war times or peace times, and mandibular trauma often results in partial bone defect. There are a lot of methods to rehabilitate mandibular defects, including bone graft and biomaterial substitues, in which autogenous bones such as ilia, ribs and fibulae are the most frequently used ones. Scholars from craniomaxillofacial departments around the world have established many traumatic animal models to study the mechanism of injury in maxillofacial region, such as Sweden Model, high speed projectile injury model, blast injury model and blast-explosive injury model in maxillofacial regions. They have studied the severity and range of bone tissue and soft tissue injury from different kinds of trauma, and determined the range of debridement, and surveyed the expression and function of various kinds of cytokines within the traumatic tissues. They concluded that mandibular defects resulting from firearm injuries could be rehabilitated in early stage, and many experiments and clinical experiences confirmed the hypothesis.Distraction Ostogenesis technique is a new method to generate newbones between bone fragments by distration devices after osteotomy. Experimental studies and clinical applications show that the mechanism of regenerate bone by DO is attributed to the ability of concrescence of bones. The periosteum and endosteum and blood supply of the distraction area and the nearby areas are the most important factors during DO procesure. The traumatic defects of mandible, especially suffered from firearm or explosive injuries, are lack of blood supply and loss of periosteum, so could we rehabilitate the defects in this situation? Could we precede the regenerate bone formation by delivery some kinds of angiogenic growth factors? Bone formation is closely linked to blood vessel invasion. Therefore, neo-formation of blood vessels in bone could enhance bone formation. Neo-formation of blood vessels in a tissue can achieve by exogenous delivery. Bone formation is preceded by vascular invasion and osteogenesis takes place in the vicinity of newly formed vessels, that mediate delivery of osteoprogenitor cells, secrete mitogens for osteoblasts, and transport nutrients and oxygen. In this experiment we simulated madibular traumatic defects to investigate the feasibility of mandibular reconstruction in this situation, loss of periosteum and lack of blood supply, and we investigate the feasibility of angiogenic growth factor delivery to precede bone formation in this situation. Four parts are included in this study. As follows:Part 1 Experimental Model of DO in the Rabbits' Mandible and theDistraction ParametersTo determine the parameters of prolonging of the rabbits' mandibles by DO after severe trauma, we simulate unilateral mandible trauma and prolong it by DO. In this study we use adultrabbits (provided by Experimental Animal Department of Fourth Military Medical University), weighing from 2.4 to 2.6kg. For every rabbit we apply mandibular osteotomy, and then introduce internal distraction devices by which both of the rabbits' mandibles can be prolonged. We destroyed the blood supply of the left mandible by removing the periosteum and cut the inferior alveolar vessels to simulate mandibular trauma. Latency period is 1 or 7 days, and distraction rate is 0.5 or 1.0mm per day, distraction length is 10 mm and consolidation period is 4 weeks. After 4 weeks the regenerate bones with 7 days latency period are better than those with 1 day latency period. DO technique can be used even after the blood supply of the mandibles are destroyed, but the latency period should be lengthened, and this may have some implications to the clinics in rehabilitation of mandible defects in early stage after trauma.Part 2 Effects of Local Appliction of rbFGF on rabbits' mandiblularprolonging by DOIn this part we simulate bilateral mandible trauma and prolong the bilateral mandible of rabbit by DO, and the distraction parameters: 7 days latency period, l.Omm/d distraction rate, 2/d, distraction length 10mm. During the latency period and distraction period we deliver FG-bFGF complex in one side of the distraction area and its vicinity, and we investigate the function of FG-bFGF. We found when mandibles are prolonged by DO after the blood supply were destroyed, the delivery of bFGF can enhance the blood vessel density of distraction areas, and after 2 or 4 weeks consolidation period the bending strength and calcium content are greatly improved as compared to the control side. This may imply we can precede bone formation during DO by delivery of FG-bFGF complex locally.Part 3 The Timing of Distraction Devices' Removal after Prolongingof Rabbits'MandibleTo determine the timing of distraction devices' removal after the prolonging of the rabbits' mandibles by distraction osteogenesis through the investigation of the regenerate bone retraction. In this study we use 16 adult rabbits (provided by Experimental Animal Department of Fourth Military Medical University), weighing from 2.4 to 2.6kg, randomly divided into 4 groups and each group 4. For every rabbit we apply mandibular osteotomy, and then introduce internal distractors through which both the two sides of the rabbits' mandibles can be prolonged. Latency period is 7days, distraction period is 10 days and consolidation period is respectively 2, 4, 8, 12weeks. Meanwhile we carry out second operation to remove the distraction devices and at the same time titanic nails are implanted by which we can measure the length changes of the regenerate bone of the mandible. After 8 weeks the regenerate bones with consolidation period of 2 or 4 weeks significantly retract, 2.1±1.2mm and 1.4±1.3mm respectively, and those with consolidation period of 8 or 12 weeks not. We conclude that the timing of removing the distraction devices applied in rabbits' mandible is 8 weeks after the completion of distraction, and if we want to remove the distraction devices earlier, the retraction must be considered.Part 4 Reconstruction of Traumatic Rabbits' Mandibular Defects byDO in Early StageWe use high speed steel balls launched by 2-stage gas cannon (made by NINT) to injure 4 rabbits' unilateral mandibles. The gas pressure is about 120kPa and the steel balls' average speed is 800m/s...