【作者】 张劲；

【导师】 柳大烈；

【作者基本信息】 南方医科大学 ， 外科学， 2010， 博士

【摘要】 1.研究背景东亚民族以女子的“瓜子脸形”或“鹅蛋脸形”为美,而面下1/3宽大,呈方形脸,甚至梯字形面型,这种男性化的面部轮廓与东南亚多数国家的人群推崇卵形脸的传统东方审美标准显然不符。下颌角是决定面下部宽度和形态的重要解剖结构,女性下颌角肥大使得外貌缺乏温柔、秀美、灵气等东方女子特有的柔美气质。下颌角肥大导致面部轮廓整形是近年来美容外科的热点。Baek等人于1989年提出下颌角肥大(Prominent mandibular angle)这一概念,其表现为颜面的方形或向外突出的外观,甚至使面部轮廓出现上小下大的形态。下颌角肥大畸形在东方人群中相对发生率较高,多数为双侧同时发生,也有仅单侧肥大者。其临床特征是下颌角较低垂,向后向下突出,下颌角角度变小,下颌角距耳垂之间的距离过大,甚至超过3cm。一般认为东方人群下颌角正常值为110-120度,女性较男性小。下颌角肥大的同时伴有不同程度的嚼肌肥大者较为常见,也有颊脂垫肥大、面部皮下脂肪肥厚等因素造成的面下部过于宽大和臃肿。面部轮廓整形是应用颅颌面外科手术技术以达到美化面部轮廓目的美容外科手术。下颌角肥大主要运用外科治疗。下颌角截骨整形手术是面型轮廓重塑中最常见的一种手术。1947年,Gumey最先采用口外入路切除咬肌外层的矫治方法；1948年,Adams首先采用口外入路下颌角截骨和部分咬肌切除的方法矫正。1951年Converse首次报道采用口内入路直线截骨法治疗下颌角肥大以来,该截骨方式已被不断改进,如1995年Yang提出的“连续多次弧线截骨”,1997年归来提出的“一次性弧形截骨”,王侠提出下颌骨弧形整体截骨。目前下颌角截骨整形术主要以口内入路为主,传统手术方法是用摆动锯或来复锯进行截骨。由于口内入路空间小,手术暴露和用锯截骨时操作困难,锋利的锯片容易损伤血管和周围组织。因此柳大烈等提出应用钻凿法进行下颌角截骨,认为此法相比传统方法有更多优点,值得推广应用。钻凿法下颌角截骨整形术作为矫治下面部轮廓整形的重要术式受到很多研究者和临床医生的关注。钻凿法下颌角截骨术在临床实际工作应用中具有截骨线设计灵活,手术创伤小,操作简单,术中出血及术后并发症少等优点,是下颌角截骨整形手术-种重要的术式。但在学习该术式时不少医师仍然担心在凿断下颌角部时的冲击力会有损伤下颌骨其他部分和颞下颌关节的可能,影响了该术式的推广应用。目前钻凿法下颌角截骨整形手术临床实际应用和相关研究中,我们面临的问题和难点主要有：①钻凿法下颌角截骨整形手术生物力学原理；②钻凿法下颌角截骨整形手术过程的生物力学状态；③钻凿法下颌角截骨整形手术的安全性及其提高措施。阐述钻凿法下颌角截骨整形手术方法的生物力学,对手术过程中下颌骨和颞下颌关节等重要解剖结构的应力分布和变形进行深入、细致的研究,三维有限元仿真分析的方法能很好的达到这一目标。2.目的和意义通过本课题研究,探索研究下颌角生物力学原理的方法和手段,建立高度仿真的下颌骨和颞下颌关节的三维有限元力学模型；通过对钻凿法下颌角截骨整形手术的仿真模拟,了解和阐述其生物力学原理；通过钻凿法下颌角截骨整形手术仿真模型,提出和分析对其的改进和优化的方法。本课题不但实现了对钻凿法下颌角截骨整形手术的仿真模拟,同时阐述了其生物力学机理,并在此基础上提出了优化和改进方法。3.方法3.1不同下颌骨三维有限元模型建模方法的比较3.1.1 Mimics直接建模法建立下颌骨三维有限元模型直接法为直接按照物体结构系统的几何外形建立节点和单元。基于女性青年志愿者头颅CT扫描图像,利用轮廓提取和阈值分割的方法提取下颌骨,删除附近其他骨骼和软组织。通过软件的三维重建和Remesh模块得到光滑连续的骨骼表面单元模型,导入Ansys软件中建立了下颌骨三维有限元模型。通过Mimics内部的FEA模块利用CT图像中骨组织内灰度信息,为每个体单元赋材料性质参数,模拟了骨组织材料性质非均匀的特性。建立了下颌骨三维有限元模型(模型-1)。3.1.2 Solidworks司接建模法建立下颌骨三维有限元模型间接建模法,需要建立物体的实体模型,再对实体模型进行自动网格划分,形成有限元模型。根据与上方法同源的原始CT图片,先在图像处理软件中进行图像分割把下颌骨分离出来,以点云形式输入到逆向工程软件Solidworks。软件对曲面域基于曲率划分,生成曲面修补,调整曲面修补的特征线消除扭曲曲面,导出曲面线框模型在Ansys软件中生成曲面,曲面围成的部分即自动生成所需的实体模型。有限元分析软件ANSYS对实体进行网格划分,生成下颌骨三维有限元模型(模型-2)。骨组织的材料参数与Mimics模型取相同值。3.1.3直接建模法和间接建模法比较为对两种建模方法进行比较分析,对Mimics直接建模法下颌骨三维有限元模型(模型-1)和Solidworks间接建模法下颌骨三维有限元模型(模型-2)采用相同的边界约束条件,在颏联合水平加载同等大小前后向冲击载荷,在同一求解器进行计算。比较两模型的Von Mises分布,对应部位应力大小进行统计学分析。3.2钻凿法下颌角截骨整形手术的生物力学研究3.2.1带颞下颌关节的下颌骨三维有限元模型的建立采用女性青年自愿者头颅CT扫描图像,间接法建立包括颅骨,上颌骨,颞下颌关节盘和下颌骨三维有限元模型。杆单元模拟咀嚼肌约束,设定下颌骨和颞下颌关节窝与关节盘为3D面-面接触关系,约束关节窝的前、后和上表面个节点和杆单元上端所有方向的位移。建立包括颞下颌关节和咀嚼肌及韧带在内的下颌骨三维有限元模型(模型-3)。3.2.2钻凿法下颌角截骨整形手术模型的建立和生物力学分析根据临床手术设计和操作方法,通过施加布尔运算,对模型3进行简化,钻孔切割等操作,模拟手术方案,建立钻凿法下颌角截骨整形手术模型(模型-4)。模拟手术操作在截骨线下缘施加载荷模拟截骨过程,根据失效准则判定失效载荷,观察分析截骨断裂过程中Von Mises应力的在分布下颌骨,颞下颌关节的分布。3.3钻凿法下颌角截骨整形手术的生物力学优化3.3.1非均匀钻孔手术设计根据截骨线局部解剖测量和失效载荷最小化的原则,在模型-4上进行布尔运算,设计了下颌骨截骨线两端钻孔加密的新截骨方式,边界条件同模型-4,建立非均匀截骨线下颌角截骨整形手术模型(模型-5)。载荷条件和观察指标同模型-4。并将计算结果与模型-4进行对比。3.3.2下颌角颊侧皮质骨去除手术设计根据截骨线局部解剖测量和失效载荷最小化的原则,结合手术实际操作过程,设计了将截骨线上内侧下颌骨外板皮质骨去除的手术方法,对均匀截骨法下颌角截骨整形手术模型(模型-4)和非均匀截骨法下颌角截骨整形手术模型(模型-5)进行优化。边界条件、载荷条件和失效准则同模型4生成去除下颌骨外板皮质骨均匀截骨手术模型(模型-6)和去除下颌骨外板皮质骨非均匀截骨手术模型(模型-7)。观察指标同模型-4,并将模型4、5、6、7的计算结果进行对比,筛选出优化下颌角截骨手术的模型。3.3.3约束条件变化对下颌角截骨手术的影响在模型-7基础上模拟肌肉的杆单元上加载最大肌力的轴向预张力建立模型-8；约束手术侧截骨线上以上下颌支后缘部分节点建立模型-9；同时采用以上两种附加约束方法模型-10。并将模型7,8,9,10的计算结果进行比较。4.结果4.1 Mimics直接建模法建立下颌骨三维有限元模型建立了下颌骨三维有限元模型(模型-1),包含皮质骨和松质骨,共214354个节点,147219个四面体单元。4.2 Solidworks间接建模法建立下颌骨三维有限元模型建立了下颌骨三维有限元模型(模型-2),包含皮质骨和松质骨,共79538个节点,73999个四面体单元。4.3 Mimics建模法和Solidworks建模法比较两模型在冲击载荷下的响应、应力传导和分布趋势是一致的；在局部的最大应力值有差异；模型-1和模型-2在冲击载荷峰值时体部、磨牙区、髁突颈采样节点von Mises应力值数据,通过SPSS13.0软件进行统计学分析,配对t检验结果,t分别为-1.496,0.450,-0.286；p分别为0.231,0.684,0.794；模型-1和模型-2之间的差异不显著(p>0.05)。4.4带颞下颌关节的下颌骨三维有限元模型的建立建立了包括颞下颌关节,颞下颌关节盘、咀嚼肌和韧带的下颌骨三维有限元模型(模型-3),包含1895460个单元,2863257个节点,24个杆单元,4个接触单元对。4.5钻凿法下颌角截骨整形手术的生物力学研究建立了均匀钻孔钻凿法下颌角截骨整形手术三维有限元模型(模型-4)；计算结果显示,下颌角断裂失效载荷为2426N; von Mises应力主要分布在截骨线下半段,同时向颏联合部传导；骨折线下半段和颏联合部都有明显的应力集中。手术侧关节盘应力较非手术侧大,大部分区域的应力值在0.56-7.54MPa之间。4.6对钻凿法下颌角截骨整形手术的改进4.6.1建立了下颌角非均匀钻孔的钻凿法下颌角截骨整形手术三维有限元模型(模型-5)；计算结果,模型-5失效断裂载荷为2018N。下颌骨von Mises应力分布显示,应力集中于截骨线下端并向颏部传导,最大应力点位于颏部,颏部红色显示的应力区域明显小于模型-4。4.6.2建立去除下颌角颊侧皮质骨均匀钻孔的钻凿法下颌角截骨整形手术三维有限元模型(模型-6)和去除下颌角颊侧皮质骨的非均匀钻孔的钻凿法下颌角截骨整形手术三维有限元模型(模型-7)；模型-6下颌角断裂失效载荷为1854N,模型-7为1447N; von Mises应力分布,模型-6和模型-7应力分布均较模型-4和模型-5明显集中,模型-7比模型-6应力分布更加集中,最大应力分布位于截骨线下半段,颏部无明显应力集中区域。4.6.3计算结果模型-8失效载荷1183N；模型-9失效载荷1028N；模型-10失效载荷876N；模型-8von Mises应力分布颏部的应力分布较模型-7明显减小；模型-9应力集中在截骨线及其上方区域内,而且较模型-7更加集中,方向与截骨线相同,下领骨其他部位应力明显减小；模型-10应力集中更加明显,应力分布范围较模型-9更小。模型-8关节盘von Mises应力大部分在0.04-0.95 MPa之间,手术侧稍大,少数区域为0.95-8.2MPa；模型-9关节盘von Mises应力手术侧较非手术侧明显增大,关节盘上面局部地方von Mises应力在32.6-45.1MPa之间,后外侧边缘甚至超过了45.1MPa；模型-10关节盘von Mises应力手术侧大于非手术侧,大部分区域为0.52-3.25MPa之间,最大不超过9.86MPa。在模型-8中肌肉韧带的拉应力最大,模型-9最小,模型-10居中但仍然小于模型-7。4.7存在的问题和今后研究展望由于人体组织结构的不规则、材料的非线性,而且大部分受力为动态,特别是颌骨组织,这对计算机提出了高性能的计算和制图能力要求。到目前为止,大多颌骨有限元模拟都基于材料线弹性假设,且绝大多数为静态力的分析,其物理相似性有待进一步提高,特别是建立具有非线性、各向异性、动态等生物力学特性的三维有限元模型,以真正向生物仿真方向发展。虽然有限元法能适应复杂几何结构及其边界条件,同时可以模拟各种外部载荷变化,但仅局限于特定个体的生物力学分析,不能代替描述力学形态的本构方程及研究对象的普遍力学规律,其进一步发展有赖于数学、物理、计算机等学科的进一步发展。现阶段生物力学有限元分析的难点在于基于标本试验和生物组织材料力学理论的材料参数的客观性评价,重点在于根据现有技术,以认识规律、发现和解决问题为目的,而不宜苛求对生物力学的定量分析。目前有限元分析法现在在医学领域还只运用于单纯的生物力学研究,如果能将有限元分析法进行的力学研究与解剖学、组织病理学、生物医学工程学等领域的研究相结合,那么有限元分析对于整个医学领域的帮助及影响将是无法估量的。5.结论根据生物力学原理结合临床实践经验,利用仿真力学实验方法,对模型进行实验条件的仿真手术,对模型在不同条件下的截骨线局部破坏极限进行分析,以失效断裂载荷最小化为标准,寻求优化的截骨方法。通过对模型的计算结果分析,我们认为非均匀钻孔的方法优于均匀钻孔的方法,去除下颌角颊侧皮质骨的方法优于不去除下颌角颊侧皮质骨的方法；在非均匀钻孔的去下颌角颊侧皮质骨手术模型上,单独增加最大咬合力约束或下颌支后缘约束与同时增加最大咬合力和下颌支后缘约束都能明显减少失效载荷,但同时施加最大咬合力和下颌支后缘约束的方法更优。更多还原

【Abstract】 BACKGROUNDWe, East Asian nation think that women with "oval face contour outline" is attractive. Mandibular angle is an important anatomic structures to determine the width and shape of the lower face,while Female mandibular angle hypertrophy makes the appearance of a lack of tender, elegant, grace and other oriental women-specific temperament. Mandibular angle contouring surgery caused by Prominent mandibular angle,in recent years, become more and more popular in our East Asian country. In 1989, Baek et al defined the concept of Prominent mandibular angle. The incidence of mandibular angle deformity in Oriental populations is relatively high, mostly bilateral simultaneous. The clinical features of the mandibular angle Prominence is the prominent mandibular angle droop down, extend toward anterior-posterior, the angle of prominent mandibular angle becomes smaller, the distance from the mandibular angle to the ear lobe is large, even more than 3cm. The normal mandibular angle in eastern population is 110 to 120 degrees, in women are smaller than men. Prominent mandibular Angle accompany by masseter muscle hypertrophy commonly, as well as hypertrophy of the buccal fat pad and facial subcutaneous fat hypertrophy and other factors affecting lower face width. Facial contouring surgery is the application of craniofacial surgical techniques to achieve the purpose of transfiguring the facial contours. The mandibular osteotomy is the most common procedure in facial contouring surgery. Traditional mandibular angle osteotomy is difficult to expose and saw because of the intra-oral approach. Recently, Liu have developed a drilling-chisel method for mandibular angle osteotomy, and deem that this method has more advantages than traditional methods, Should be widely applied as well.In clinical application, The drilling-chisel method for mandibular angle osteotomy have been validated that have the advantages with controllable osteotomy line design with convenient, simple, minimally invasive, less intra-operative hemorrhage and postoperative complications. Before accepting this method, however, many surgeon remain concerned about that the impact may damage temporomandibular joint and other parts of the mandible, so that the popularization and application of this surgical procedures were limited.In the clinical application and relevant researches on the drilling-chisel method for mandibular angle osteotomy, there are still a few questions.①Biomechanical mechanism of the drilling-chisel method;②Biomechanical status of the whole process of the drilling-chisel method;③Beliability of the drilling-chisel method.For in-depth, detailed study on biomechanics of the drilling-chisel method for mandibular angle osteotomy during surgery, three-dimensional finite element analysis method can be very good to achieve this goal.OBJECTIVEThrough this research project, to explore the methods and means of establishing a three-dimensional finite element model of mandible and temporomandibular joint with high similarity;by simulating of the drilling-chisel method for mandibular angle osteotomy, to understand the biomechanical principles;propose and analysis the approaches to improve and optimize the drilling-chisel method.METHODS1 Comparison of different modeling methods of mandibular FEA model 1.1 The direct modeling method to establish three-dimensional finite element model of mandible by MimicsDirect method establish the nodes and elements in accordance with the geometry of the structure system of the object. Based on a young female volunteer head CT scanning images, using contour extraction and threshold segmentation to extract the mandible, remove bone and soft tissue nearby. Using the three-dimensional reconstruction and Remesh modules, obtained a smooth and continuous bone surface element model,inported into Ansys software to create a three-dimensional finite element model of mandible. Mimics FEA module through reading grayscale information of CT images of bone tissue and assigned material parameters for each element, we can simulate the heterogeneous nature of bone tissue material properties, and established Model-1.1.2 Indirect modeling method to establish three-dimensional finite element model of mandible by SolidworksBy indirect method, first establish the physical model of the object, and then the solid model is automatically meshed to form a finite element model. According to the same original CT image, First used an image processing software for image segmentation to separate the mandible from other tissues, and the point cloud format file was entered into reverse engineering software Solidworks. software divided surface based on the curvature domain to generate patch surface, adjusted the surface characteristics line to eliminate distortions in surface; wire frame model generated surface model in Ansys software, surrounded part of the surface model generated solid model;Finite element analysis software ANSYS meshed entities to generate the final three-dimensional finite element model (model-2). Bone tissue material parameters assigned the same value of model-1.1.3 Comparison of Mimics model and Solidworks ModelFor the comparison and analysis the two modeling methods, three-dimensional finite element model of mandible by the direct modeling method using Mimics and three-dimensional finite element model by indirect modeling method using Solidworks, adopted the same boundary conditions, losded the same level of anterior-posterior impact load at the mental symphysis; calculated in the same solver and compared the the magnitude and distribution of Von Mises stress of two models.2 Biomechanical Study on the drilling-chisel method for mandibular angle osteotomy2.1 The establishment of three-dimensional finite element model of mandible and temporomandibular jointBased on a Youth female volunteer’s head CT scanning images, by the indirect method, we established the three-dimensional finite element model of mandible (model-3)comprising glenoid fossa, temporomandibular joint disc and masticatory muscles and ligaments of the mandible. Link element simulated the masticatory muscles and ligaments, defined the mandibular condyle,articular fossa of temporal bone and the articular disc as the contact element, constrainted the nodes in all directions of displacement of fossa surface and top of link elements..2.2 The drilling-chisel method for mandibular angle osteotomy operation modeling and biomechanical analysisAccording to clinical procedure, through Boolean operation, we modified the model-3 to simulated drilling holes on mandible, then the drilling-chisel method for mandibular angle osteotomy model (Model-4) was established. Applying the impact loads at the lower edge of osteotomy line simulated osteotomy procedure. Based failure criterion to determine the failure load, observed the distribution and magnitude of Von Mises stress during the procedure.3 Biomechanical optimization of the drilling-chisel method for mandibular angle osteotomy3.1 Non-uniform drilling method for mandibular angle osteotomyFollowing the principle of minimize the failure load, we designed a new drilling fashion which increased the number of drilling at both ends of osteotomy line. Other conditions same as with the model-4,then we established Model-5 and compared the results with model-4’s.3.2 Mandibular angle buccal cortex removal method According to local anatomical measurement and the optimization principles, combined with the actual surgical operation, we designed a optimized method to remove buccal cortex of mandibular angle of model (model-4) and non-uniform drilling osteotomy model (Model-5), other conditions same as with the model-4,then we got the model-6 and model-7. All the calculation results of model-4,5,6,7 are compared with each other and selected the mandibular angle osteotomy optimization model.3.3 The contribution of constrain condition to the mandibular angle osteotomyBased on model-7, loaded the axial Pre-tension on the link elements to simulated the max muscle contraction force, we established model-8; constrained the nodes on the posterior border of the mandibular ramus over the osteotomy line, we established Model-9; and applied all of two constrain conditions on Model-7,we established Model-10. The computing results of Model-7,8,9,10were compared with each other.RESULTS1 Comparison of different modeling methods of mandibular FEA model5.1 The direct modeling method to establish three-dimensional finite element model of mandible by MimicsWe established the mandibular three-dimensional finite element model (model-1), comprising cortical bone and cancellous bone,214354 nodes,147219 tetrahedron elements.5.2 Indirect modeling method to establish three-dimensional finite element model of mandible by SolidworksWe established the mandibular three-dimensional finite element model (model-2), comprising cortical bone and cancellous bone,79538 nodes,73999 tetrahedron elements.5.3 Comparison of Mimics model and Solidworks ModelIn the peak load, the von Mises stress value of each node on corresponding parts of each model analysised by paired t test, and the result showed that the differences between the two groups of data has no significant (p=0.761). 2 Biomechanical Study on the drilling-chisel method for mandibular angle osteotomy2.1 The establishment of three-dimensional finite element model of mandible and temporomandibular jointWe established a three-dimensional finite element model of uniform drilling mandibular angle osteotomy (Model-4).2.2 The drilling-chisel method for mandibular angle osteotomy operation modeling and biomechanical analysisThe results showed that the failure load of mandibular angle is 2426N; von Mises stress mainly distribute near the lower half of the osteotomy line, while conduction to the mandibular symphysis; the value of von Mises stress in left TMJ articular disc is larger than right’s, the stress values in most regions is between 0.56-7.54MPa.3 Biomechanical optimization of the drilling-chisel method for mandibular angle osteotomy3.1 Non-uniform drilling method for mandibular angle osteotomyWe established the three-dimensional finite element model of non-uniform drilling method for mandibular angle osteotomy (Model-5) and loaded. The computing results showed that the failure load of mandibular angle was 2018N; Von Mises stress distribution in the mandible showed that stress concentrated at the lower half of the osteotomy line and the mandibular symphysis, the red area showed the peak value of stress is smaller than Model-4.3.2 Mandibular angle buccal cortex removal methodWe established the three-dimensional finite element model of mandibular angle buccal cortex removed uniform drilling method for mandibular angle osteotomy (Model-6)and mandibular angle buccal cortex removed non-uniform drilling method for mandibular angle osteotomy(Model-7), loaded as well. The computing results showed that the failure load of mandibular angle of Model-6 was 1854N and Model-7’s 1447N; the distribution of von Mises stress of Model-6, and Model-7 were more concentrated than in Model-4 and Model-5,while it was more concentrated in Model-7 than in Model-6.3.3 The contribution of constrain condition to the mandibular angle osteotomyThe computing results of Model-8,9,10 showed that the failure load of mandibular angle of Model-7 was 1183N and Model-9’s 1028 N,Model-10’s 876N;von Mises stress distribution of Model-8 were more concentrated than the model-7 with a smaller stress concentration zone of mandibilar corpus, stress in Model-9 concentrated in the region near the osteotomy line and the upper area, the conduct direction same as the osteotomy line. In Model-10, von Mises Stress concentrated in a narrow region around osteotomy line.CONCLUSIONAccording to biomechanical principles and clinical experience, using the mechanical simulation experimental method, established the model of simulation surgery, we analysised the mandibular angle osteotomy. To minimize the failure load, we designed a series of 3D finite element model of mandibular angle osteotomy. Computing and analysis these models, we believe that non-uniform drilling method is better than uniform methods; the mandibular angle buccal cortex removed non-uniform drilling method for mandibular angle osteotomy is superior to the method that without removing the buccal cortical bone of mandibular angle and mandibular angle buccal cortex removed uniform drilling method for mandibular angle osteotomy.Based on the mandibular angle buccal cortex removed non-uniform drilling method for mandibular angle osteotomy model, Constraints imposed by the maximum muscle contracting force alone or constraints at the posterior border of the mandibular ramus and also applied them all can significantly reduce the failure load, but to impose constraints at the posterior border of the mandibular ramus approach are more favorable and reliable.更多还原