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1、 Amira与UG及ALGOR软件联合建立下颌磨牙三维有限元模型 作者：杨萍，张少锋，刘继鹏，周冰，孟庆岩，高婧【摘要】
2、 目的：建立人下颌区三维有限元模型. 方法：采用薄层CT扫描技术、医学影像三维重建软件Amira和Unigraphics NX造型软件以及有限元分析软件ALGOR相结合建立下颌567及其支持组织的三维有限元模型. 结果：建立了下颌区三维有限元模型，总节点为93 260个，六面单元数为167 111个. 结论：所建模型结构完整，空间结构测量准确度高，单元划分精细、能够较精确地模拟实体状态，为进一步的生物力学研究提供了基础. 【关键词】 有限元分析法0引言有限元分析法(finite element analysis method，FEAM)是一种理论力学的分析计算方法，近年
3、来,随着电子计算机技术的飞速发展和各种功能齐全的软件开发, 已被广泛运用到口腔医学领域中用于各种复杂问题的力学研究.该方法的基础是模型的建立，如何提高模型的相似性是研究的重点1 ，只有提高模型的相似性，才能保证实验结果的准确性. 由于牙颌组织外形结构复杂，以往建模难度大，花费高，建模时问长. 我们将薄层CT扫描技术、医学影像三维重建软件Amira，Unigraphics NX以及有限元分析软件ALGOR相结合建模，对如何提高有限元模型精确性、加快建模的速度、简化建模过程进行探讨.1材料和方法1.1材料GX26O商用台式机(处理器Intel Pentium 43.0 G，内存2 GB，硬盘250
4、 GB，操作系统Windows 2000 Professiona1)；PQ6000螺旋CT扫描机(美国Picker公司)；应用软件Amira4.0（美国TGS公司）；UGNX4(美国EDS公司)；有限元分析软件ALGORv19（美国ALGOR公司）；根据参考文献2，选择一牙列完整、咬合关系正常、无明显牙周疾患及牙槽骨吸收成年男性志愿者，作为下颌牙列及下颌骨三维形态数据测量的样本.1.2方法1.2.1CT扫描及原始数据的获取测试者取仰卧位，颏部抬高，头部固定，戴用预制咬合板，避免上下牙列接触. 用螺旋CT扫描机进行扫描，层厚0. mm，选择得到断层影像100张，将扫描图像在CT工作站转换为bmp
5、格式文件，记录并存入计算机.1.2.2图像的三维重建将得到的bmp文件输入医学影像三维重建软件Amira中，读取二维图像数据生成牙齿的三维点云图（图1），转换为可以在UG中输入的tiff格式,再将模型导入UG造型软件实体网格构建. 将多面体网格填充方式由点云形成粗略实体，以牙冠为特征形成XY轴，使用UG中的Imageware模块对齐坐标轴，进行点云拟合和形成髓腔. 平行切割点云形成相交线. 利用已得到的相交线，通过曲线命令形成牙体根部，用缝合命令封闭根尖端完成髓腔实体. 用布尔运算形成牙的实体，将模型保存为igs格式（图2）.图1图2略1.2.3三维有限元模型的建立将建立的三维空间模型数据导入
6、有限元分析软件中，利用ALGOR中分析模块对模型进行自动网格划分，采用8节点六面体单元自动、依次划分各部分的单元，获得三维有限元模型. 根据要求设定材料特性、边界条件，假设模型中的各材料和组织为连续、均质、各向同性的线弹性材料；其近远中径及底部完全固定，受力时模型各界面均不产生相互滑动. 参考文献3-5 ，所用主要材料参数如表1所示.2结果建立了下颌567实体模型， 将模型导入有限元分析软件ALGOR后， 采用8节点六面体单元自动、 依次划分各部分的单元， 获得三维有限元模型(图3). 建成的模型总单元数167 111个， 节点数93 260个， 其中下颌5单元数为36 093个， 节点21
7、830个， 下颌6单元数为73 984个， 节点40 694个， 下颌7单元数为57 034个， 节点30 736个. 所构建的有限元模型能够以单独或组合的方式观察各组成部分的情况， 还可以按照不同的研究目的和要求进行删除、 旋转、 切割和添加， 方便个别修改和调用. 表1有关材料的力学参数略3讨论3.1三维有限元模型建立的基础FEAM分析研究的基础是建立有限元模型，理想模型的建立是准确计算和分析的前提. 而二维截面的生成是模型与实体相似度高低的关键，CT扫描技术具有定位准确，准确再现复杂细微结构，数据精确及可重复使用等优势. 故我们选择此方法较好地再现了牙颌组织结构. 建模过程中，由于牙齿的
8、表面形态及内部结构细微复杂，在建模过程中反映其真实形态难度很大，尤其是磨牙的建模更为复杂，以往建模过程中部分方法不能获得精细的解剖外形及内部结构. 面对模型的“简化”意味着几何信息不准确，会对应力分析结果造成影响6. 我们选用Amira建模软件将二维图像数据转换为牙齿的点云分布图，排除了人为因素的影响，再利用专业造型软件UG生成实体模型，从而使模型具有可调性，精确到点，不存在简化，点控制曲线，由曲线控制曲面，再由曲面生成三维实体模型. 这样所建模型完全符合实际形态并可进行快速分析.3.2逆向工程建模优势牙齿的几何形状较为复杂，属于多材质复合组织，通过常用的有限元软件实体建模工具很难构建几何相似
9、性良好的牙齿有限元模型，需要利用逆向建模(reverse modeling)技术7， 即将已有的牙体模型通过测量扫描及各种先进数据处理手段获得实体信息，进行数据处理手段获得实物信息，然后利用CAD(computer aid design)技术对牙体实物进行各曲面、尖、窝、嵴的实性造型，从而得到原件的CAD模型. Imageware作为UGNX中提供的逆向工程造型软件，具有强大的测量数据处理、曲面造型、误差检测功能. 可以处理几万至几百万的点云数据. 建模过程中最关键的环节即利用Imageware进行点云的正交化，以此来避免因未正交化导致的不符合牙齿正常形态，导致信息的丧失. 正交化后的模型经逆
10、向工程检测生成的牙齿与点云间最大均方根值<0.1，有效的保证了模型的精度. 建模中存在的另一个问题是生成了高阶复杂曲面，其产生原因是由于牙齿的特殊解剖特性所致1，而有限元内并不支持高阶曲面，导致模型不能倒入有限元分析软件ALGOR中进行网格的划分，对此我们利用UG中曲面编辑功能形成样条曲线（低阶3），必须经过点-线-面-线-体的建模过程，根据先前所描记的模型各层轮廓线上的各个点的坐标UG便可自动建立近似几何实体，由此建立起来的三维有限元模型形态与实体具有较好的几何相似性，可以代表实体的真实形态，得到一个即忠实于点云实体，又能被ALGOR划分出有效网格的模型.3.3有限元网格的划分用于三维
11、几何模型进行有限元单元划分的网格类型主要包括：六面体单元、四面体单元、三棱柱单元等. 六面体网格具有较高的精度，但划分难度高,较难实现自动网格划分，而我们所用有限元分析软件ALGOR，采用8节点六面体依次划分，可自动生成美观、精度高的有限元网格，并可模拟各种结构形式及各种复杂材料. 网格划分时进行网格参数设置并分网，若网格可以接受则进入分析环境，若网格不能接受则修改控制参数或者进行网格细化. 在划分单元时，单元的大小(网格的疏密)要根据精度的要求和计算机的速度及容量来确定，对部分细微结构及应力和位移变化较剧烈的部位采取网格加密，避免信息损失.综上所述，我们将采用CT扫描技术与CAD软件和有限元
12、分析软件共同建模，所建立的牙齿几何相似性好，有效的提高了建模精度和建模速度，单元划分精细，模型可任意旋转观察、切割及调整并可重复使用. 从而为进一步的优化修复设计提供了可靠依据.【参考文献】 1 Baumrind S， Kom EL， Boyd RL. Apical root resorption in orthodontically treated adultsJ. Am J Orthod Dentofacial Orthop，1996，110(4): 311-320.2 王惠芸. 我国人牙的测量和统计J. 中华口腔医学杂志,1959，7(3): 147-153.3 Chang
13、KH，Magdum S，Khera SC. An advanced approach for computer modeling and prolotyping of the human toothJ. Ann Biomed Eng，2003, 31(5)：621-631.4 Toparli M. Stress analysis in a postrestored tooth utilizing the finiteelement methodJ. J Oral Rehabil，2003,30(5)：470-476.5 Farah JW，Powers JW，Dennison JB，et al.
14、 Effects of cement bases on the stress and deflections in composite restorationsJ. Dent Res，1976，55(1)：15-20.6 田力丽,李凌曼. 逆向工程技术法构建牙体缺损修复的三维有限元模型J. 实用口腔医学杂志, 2006，22（4）：502-505.7 李作广. 生物组织有限元建模与分析J. 同济大学学报，2002，30(3)：356-358./Porganization system and working mode, the selection of a number of municipa
15、l strengthening group to build innovation and strengthen the organization of the basic level organizations advanced model.(seven) the manual work of the Communist Youth League Organization published and League branch of manual work, to promote the use of two manuals in the citys organizations at var
16、ious levels. The county committee, directly under the group (work) is under the jurisdiction of grassroots League and group (total) using branch ratio shall not be less than 70%.Three, to further strengthen the groups leadership and team building(a) to strengthen the leagues leadership at all levels
17、 of construction. Continue to do a good job of municipal Party Committee Organization Department on the strengthening of the Communist Youth League cadres management opinions implementation. To promote the group counties (autonomous counties, cities) Commission and city directly under the group (wor
18、kers) appointed to carry out the Five team building activities. Improve the League Association Department working mechanism. Conscientiously fulfill the duties of CO, combined with the city group directly under (the) Committee of the general election and the adjustment, actively jointly with the uni
19、t where the party organization department good group leadership selection with the work. Do a good job in municipal Party committee assistant committee leadership and leading cadres of the annual assessment work, adhere to and improve the assistant secretary of the Communist Youth League talk system
20、 group To weave individual conversation and collective conversation, to strengthen the committees of all levels, the Standing Committee of the Standing Committee, the establishment of a sound system of central group learning, the system of investigation and study, the system of important issues and
21、the reporting system.(two) to strengthen the work of education and training of cadres to conscientiously implement the Central Committee. On the implementation of grassroots cadres training project and opinions on carrying out the mission municipal CYL Cadres training project implementation opinions
22、, full implementation of the project of the City Youth League cadres training education. Focus on the county grassroots cadres and workers focused on training, the new school system vocational training League cadres, for the Municipal Organization Department jointly held the third session of the Com
23、munist Youth League system training cadres in party. Focusing on the construction of new socialist countryside, strengthening village cadres and rural construction team group member of the young team, the county organizations at various levels throughout the year is expected to train 100 00 rural gr
24、assroots cadres, plans to train 1000 village secretary of the village Party branch.(three) actively promote grassroots cadres election work. Under the unified leadership of the party organization, to strengthen grassroots organizations direct work, standardize the election work rules and procedures,
25、 in the designated candidate, open competition to democratically elected branch secretary at the same time, actively and steadily the development of Township, streets and other grassroots organizations in the direct election of the pilot work, on the basis of summarizing the experience and gradually
26、 expand the scope of the pilot, and gradually formed a set of measures and cadres election system.(four) to strengthen the cadres testing exercise. To study the development of XX city from 2006 to 2008 cadres testing exercise planning. To select outstanding cadres to the central mission in Beijing,
27、Shanghai, Guangzhou and other central organs and sending work in developed areas. With the Central Committee the implementation of the western region and ethnic minorities cadres training plan . To carry out the eighth batch of municipal organs attachment cadre management, selection, training work.
28、The outstanding cadres to start the National Development Bank XX branch testing exercise.(five) to strengthen the group construction. The main position to play the role of Youth League cadre education and training as the city, in accordance with the requirements of post training, further curriculum
29、scientifically and rationally, adopt arrangement menu course, basic theory includes group work, focus, hot and difficult issues, to enhance the content and practice; to strengthen the construction of teaching staff, the integration of teachers, establish a quality teacher training team, establish an
30、d implement course evaluation system; take delivery of training to the countryside, on-site training, and increase the rural grassroots cadres training efforts.Four, efforts to strengthen the work of young talent(a) to tenth XX young 54 medal in recognition of the publicity, and actively explore the
31、 XX youth service. 54 Medal of institutionalization, standardization and socialization mechanism. Give full play to the XX award in recognition of 54 youth medal Association, Youth Award winner in the 54 chapter, investigation activities. Who won the Youth Service medal, dedication to the society to
32、 create conditions, build the stage. During the 54, named in recognition of the tenth XX young 54 medal. The association of XX editing of young talent , the exchange of information and communication platform for the XX of outstanding young talents.(two) the establishment of municipal Party committee
33、 of young talent information database. In accordance with the feasible, effective, classification management, implement step by step principle, the establishment of municipal Party committee of youth talent database; guiding organizations at various levels generally established the young talent data
34、base, construction of city, county (directly under the Communist Youth League), grassroots organizations three young talent information database the relevant information collection system, and gradually establish the citys young people, the Communist Youth League youth talent information network, pr
35、ovide information platform for young talent resource development.Five, take effective measures to strengthen the mission management(a) to strengthen the mission management work. Strengthen the dues collection and management, continue to adhere to the dues collection regularly reporting system, the a
36、nnual comprehensive award in recognition of the tour and the tour one vote veto system audit system. Do statistical work in the group. The group service award in recognition of the advanced units, standardization, promoting group management work institutionalized.(two) to strengthen the organization
37、 of research and information exchange efforts. Grassroots carry out research, efforts to form a number of theoretical results. Make full use of the network carrier, to explore the establishment of electronic group service system, promote the work of Communist Youth League information.Attachment 4:XX
38、 municipal Party Committee Propaganda Department of the Communist Youth League work pointsIn 2006, the Communist Youth League propaganda ideological work XX to Deng Xiaoping theory and the important thought of Three Represents as guidance, study and implement the partys sixteen and the spirit of the
39、 the fifth Plenary Session of the 16th CPC Central Committee implementation of the eight plenary session of the two committee, the citys cultural work conference, the Propaganda Department of the meeting and the the fourth Plenary Session of the 15th CPC Central Committee permanent mission spirit, c
40、losely around 11th Five-Year XX the goal of full implementation of Scientific Outlook on Development, emancipating the mind, seeking truth from facts, keep pace with the times, close to reality, close to life, close to the young, persevere grasp orientation, grasping deepening, grasping construction
41、 innovation, further improve the groups propaganda and ideological work ability, unity To guide the majority of members of the youth to achieve the 11th Five-Year planning tasks, the overall construction of a well-off society, building a socialist harmonious society to make new contributions.One, ad
42、here to the Three Represents important thought and Scientific Outlook on Development education to guide the youth, to further strengthen the ideological and political education of youth(a) armed with youth science theory. Unremittingly with Deng Xiaoping theory and the important thought of Three Rep
43、resents armed members of youth education, to promote the study and implement to expand the depth and breadth. To study and implement the important thought of Three Represents with the establishment and implementation of Scientific Outlook on Development combine with the implementation of the require
44、ments of constructing socialist harmonious society with Scientific Outlook on Development, carry out education as an important part of the theory of armed youth in the new period, strengthen the establishment and implementation of Scientific Outlook on Development education, educate and guide the yo
45、uth to fully understand the great significance of establishment and implementation of Scientific Outlook on Development, in-depth understanding of the Scientific Outlook on Development era back The king, the practice foundation, basic connotation, historical status, spirit and practice requirements,
46、 a profound understanding of Scientific Outlook on Development with Marxism Leninism, Mao Zedong thought, inheriting and developing relationship between Deng Xiaoping theory and the important thought of Three Represents, to help young people establish and consciously practice Scientific Outlook on D
47、evelopment. Persist in learning, grasping the backbone, grasp the practice, grasp the opportunity. Catch club, effective way to grasp the network, with the group of cadres, young students and young backbone fronts as the focus, to promote the work of the armed youth theory to develop in depth, to he
48、lp the youth continue to firm ideals and beliefs, to build a powerful spiritual pillar. To carry out the study and implementation of the partys sixteen session of the five Eight plenary session of the two plenary session of the Central Committee and the party spirit, to the citys Youth League members thinking into the spirit of the meeting, to achieve the goal of national consciousness and XX economic and social development in 11th Five-Year period. Contribute to help and guide the youth to a profound understanding of the significance and main task of building a socialist harm
