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Internal Nitinol Distractor:Application in Segmental Mandibular Reconstruction

Author: ZhouHongZhi
Tutor: LiuHongChenï¼›HuMin
School: PLA Postgraduate Medical School
Course: Clinical Stomatology
Keywords: Distraction osteogenesis Mandible Reconstruction Nitinol Guided bone regeneration
CLC: R782
Type: PhD thesis
Year: 2003
Downloads: 49
Quote: 1
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Abstract


Objective Rational design of distractor is the foundation of distraction osteogenensis. Continuous distraction, by using internal automatic distractor, can reduce suffering of patients and avoid tiresome procedure of manual distraction. Furthermore, it is more feasible for bone regeneration. Some recent researches have been focused on this thesis and are considered important for further development of distraction osteogenesis. The aims of this study are to develop multi-purpose and self-activated internal distractor, utilizing shape memory and super-elasticity of Nitinol, and to establish practicable surgical technique for segmental mandibular reconstruction via continuous elasticity distraction osteogenesis using Nitinol distractor.Methods First we created a rabbit model for preliminary feasibility research of elasticity distraction in segmental mandibular ramus reconstruction. Ramus segment of 1.5cm, including the condyle, was removed from one side of rabbit mandible. The S shape distractor, made from 0.8mm Nitinol wire, was settled without .latency to perform bone transport. The incision was closed. Final results of mandibular reconstruction were observed 2 months later. Then a canine model of segmental mandibular reconstruction was created for further investigation of surgical technique suitable for elasticity distraction. Segmental defect of l~3mm was created in canine mandibular body and bifocal distraction was performed without latency using W shape Nitinol distractor made from 1.33mm wire. Several experimental groups were divided according to the size of defect, methods of transport disc formation (osteotomy or corticotomy), methods of transport disc guidance (with or without Kirschner pins). The osteogenesis results were compared to search for feasible surgical operation. Based on the established canine model of elasticity distraction, we observed the effect of strength and stretch distance of Nitinol distractor on distraction osteogenesis. Several kinds of distractor, which stretch distance was 4cm or 6cm, were made from 1mm and 1.3mm and 1.33mm Nitinol wire. Their constriction-recovery elasticity curves were measured beforehand. Canine models of 4cm segmental mandibular defect were created and divided into groups to fixdifferent distractors. The rate and distance of distraction osteogenesis were measured afteroperation.The canine models of 4cm segmental defect were duplicated, and 1.3mm and 1.33mmdistractors were used to create regenerate bone segment longer than 3cm. Then the animals weresacrificed at different time after operation for examination of bone density and intensity, so as toget primary knowledge of bone regeneration and rebuilding process in elasticity distractionmode.We further investigated the possibility of combination of guided bone regeneration withdistraction osteogenesis. After the canine segmental mandibular defect was created and Nitinoldistractor was settled routinely, a piece of ePTFE membrane was sutured and covered the buccalside of the bone defect and distraction gap. The osteogenesis results were observed andcompared with that of none membrane guided distraction 3 months later.To improve the design of transport disc guidance by Kirschner pins, we used reconstructive plateand micro-plate to form new device for fixation and guidance. To testify its feasibility, weapplied it with Nitinol distractor in trifocal bone transport reconstruction of canine mandibularmentisResults The rabbit model proved feasibility of elasticity distraction in principle. Regeneratebone segment of 0.8-1cm was formed in distraction zone with bony connection to normalmandible. The ramus was reconstructed. Radiograph of the regenerate bone showed wellossification and micrograph show histological appearance similar to intramembranousossification with regular arrangement of cortical bone lamella and bone trabecula according withdistraction direction.Further researches in canine model revealed that, when performing elasticity distraction, tr

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