| Background: the mandible lies in one of the third of the lower and the middle face. Mandibular fracture is a relatively common occurrence because of the big area and the projection. Fractures of the angle,body and symphysis region represent the most percentage of mandibular fractures. The aim of the treatment for mandibular fracture is to restore the normal occlusion relation and the physiological function of lower jaw. For the long time the treatment for mandibular fracture is the intermaxillary traction and intermaxillary fixation using of the arch splint, which can restore and keep the nomal occlusion relation until the wound healing. However clinically, this treatment brings much pain and inconvenience to patients, restricted to many conditions, not accord with the require of biomechanics and with many postsurgical complications. So people try to develop some more scientific treatments. In the middle of the last century, people have realized the new mechanism of the healing of the fracture, that is keeping the stability to the fragments is very important to the wound healing normally and quickly. From then on, the technique of the rigid internal fixation using dynamic compress plate, eccentric dynamic compress plate have used for the treatment of mandibular fracture. However the long-time clinical retrospective study showed that there were high rate complications such as infections and malocclusion due to the large plate which can not be bended to be suitable for the complex surface of mandible and long time wound explosure, excess pilling and pulling of the parenchyma. So the dynamic compress plate and eccentric dynamic compress plate were replaced by the mini-plate in 1980s. In 1970s Champy et al reported a new treatment of mandibular fracture using miniplate system, which could avoid an external scar and reduce the complications of malocclusion due to placed transorally and easily bended to suitable to the surface of the mandible. But the small plate reduced mechanical properties because of the small volume and modulus of elasticity, and still gave rise to the questionwhether they were stabile enough for mandibular fracture fixation. Purpose : a three-dimension finite element mathematical model of mandibular fracture was used to analyse the stability of the titanium mini-plate when used to rigid internal fix the mandibular fracture and discuss the relationship between the incline angle of the body and the stability of the fragment after titanium mini-plate rigid internal fixation. Materials and Methods: a mandibular three-dimension finite element model was developed. The data came from a male volunteer who had the full dentition,healthy periodontium and normal occlusion relationship. The orbital –ear plane was as the basal plane ,scanned through spiral CT ,selected the bone tissue windows to study the floors, registered the coordinates value of the every floor of the borderline of bone tissue, then inputted the value into the SolidWorks2002 finite element software, thus developed the mandibular three-dimension finite element model. The each material parameter was defined, and the bone nature of the mandible was supposed tothe isotropy .Angle,body and symphyseal single line fractures were simulated in vitro. The fractures were fixed by the titanium mini-plate according to the Champy's ideal fixture line of the mandibular fracture, and the displacement of the fragments was attained by simulating occlusion on incisors, molars of the fracture side and non-fracture side. Analysed the research results and then enactmented different mesial incline angles of the fracture line in body, calculated and registered the displacement of the fragments. Result: The study has showed that at the situation of occlusion, the fragment can mobile wherever the fractures are. The displacement in symphysis and body fractures with rigid internal fixation was within 150μm when function occlusion. To angle fractures, the displacement of the fragment was also within 150μm when incisors occluded, but larger when both fracture side and non-fracture molar occluded. When the incline angle of the fracture line in body was over 20 degree, the displacement was over 150μm. Conclusion: At the situation of occlusion ,the fragment of... |
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