可摘局部义齿各部件三维有限元模型库的建立

目的 建立可摘局部义齿各部件的三维有限元模型库。方法：在正常牙颌组织及可摘局部义齿三维几何学模型库的基础上，利用Powershape、Pro/E和Ansys 5．5软件，通过数据转换、模型分割修整、重建，分别建立各模型单元体，并在整体模型中连接、修整，最终生成各类有限元模型库。结果：建立了包括(牙合)支托、卡环、基托、人工牙、连接体等共计200余个有限元单元体，分类生成8类有限元模型库。结论：各类模型具有良好的几何学形态，在整体模型中组合完好，调用、编辑便捷。     

固定义齿各部件三维有限元模型库的建立

目的 建立固定义齿各部件三维有限元模型库。方法：在正常牙颌组织三维几何学模型、模型库的基础上，利用Powershape、Pro/E和Ansys5.5软件，根据天然牙牙冠模型建立基牙一固位体单元体，以及桥体单元体，在牙冠间隙中新建连接体单元体。结果：建立了固定义齿各组成部分的有限元模型库，包括固位体、桥体、连接体3个模型库82个单元体。结论：各类模型具有良好的几何学形态，力学模型组建过程快速、简便。     

牙颌组织及修复体三维几何学、有限元模型的设计

目的 建立口腔修复各类模型及模型库系统。方法 以正常颌骨及牙弓为样本，在CT技术及计算机软件（PRO／E，ANSYS等的）的帮助下，首先建立部分上颌骨及下颌骨的三维几何学模型和有限元模型，再建立牙颌组织和修复体的各类模型库，最后探讨模型和模型库的应用方法。结果 建立了部分上颌骨，下颌骨，牙列及修复体的三维模型及模型库。结论 模型具有较好的力学相似形和几何学相似形，模型库应用高效方便。     

不同高度牙周支持组织的下颌前磨牙三维有限元应力分析

目的：观察不同牙周支持高度的牙齿受力时，牙体内部尤其是牙根的受力的状况。方法：以电子计算机技术建立了包括牙齿、牙周膜、硬骨板、松质骨和皮质骨的下颌前磨牙三维有限元模型。分别删去2层、4层、6层牙周支持组织(分别占牙周支持高度的20%、40%、60％．)产生代表4种不同牙周支持高度的三维有限元模型。分别计算出不同同载荷下不同牙槽骨高度下牙体组织的最大拉应力、最大压应力和Von Mises应力。结果：随着牙槽骨的降低，牙体组织内的最大等效应力和最大压应力都逐渐增大，最大拉应力变化不明显。最大应力部位由牙颌部逐渐移至牙根中部。结论：健康的下颌前磨牙较牙槽骨有吸收的下颌前磨牙更易患楔状缺损。而牙槽骨吸收的下颌前磨牙较止常下颌前磨牙易根折。     

中山市民众镇中学生牙颌畸形调查分析

目的：了解中山市民众镇中学生牙颌畸形的发病情况。方法：对中山市民众镇3所中学初一至高三的3120名学生的恒牙列牙颌畸形情况进行调查和统计学分析。结果：民众镇中学生牙颌畸形的总发病率为34．17％，以Angle I类错He及牙列拥挤发病率为最高，分别为27．02％和19．65％，88．09％的牙颌畸形患者缺乏正畸治疗意识。结论：民众镇中学生牙颌畸形的发病率相对偏低。     

下前牙缺失3种固位方式基牙及牙周组织所受应力的有限元分析

目的：探讨在相同的缺牙病例中,不同的固位体设计（固位体的类型、放置的位置）对牙颌组织的力学影响.方法：对个别牙缺失的病例设计不同固位体,在可摘局部义齿三维有限元模型库的基础上组建实验模型,通过三维有限元方法,分析牙周组织在不同情况下所受的应力大小.结果：在3种不同的固位体设计方式中,固位体放置在第二前磨牙与第一磨牙之间时,基牙及牙周组织受力最小;固位体放置在第一前磨牙与第一磨牙上,基牙与牙周组织受力最大.结论：应依据基牙与牙周组织的健康状况,选择最佳固位方式.     

下颌牙列三维光弹模型的设计和制作

目的 探讨下颌牙列三维比弹模型的设计和制作。方法 根据相似性原理，用不同弹性模量的环氧树脂模拟牙体、牙槽骨，用硅橡胶模拟牙周膜制作下颌牙列三维光弹模型，结果 制作了与实体相近的下颌牙列三维光弹模型。牙体、牙槽骨及牙周膜的弹性模量之比为13．2：1：0．0003。结论 该三维光弹模型可用于定性分析牙周支持组织的应力分布情况。     

固定桥基牙牙槽骨吸收三维有限元模型的建立

目的:通过建立左侧下颌后牙5单位固定桥双基牙侧牙槽骨吸收的有限元模型,为分析双基牙侧牙槽骨吸收对牙周膜应力的影响打下基础。方法:采用多层螺旋CT扫描技术与Mimics、Ansys软件相结合对88张层厚为0.6mm的CT断层影像进行三维重建,在此基础上建立双基牙侧牙槽骨吸收模型。结果:建立了5单位固定桥有限元模型及双基牙侧牙槽骨吸收的有限元模型,包括牙齿、牙周膜、牙槽骨。结论:所建模型结构完整,单元划分精细,能够较精确地模拟牙槽骨吸收的实体状态,为加载后的基牙牙周膜应力分析提供基础。     

个体化舌侧矫治器微种植体支抗滑动法内收上前牙的三维有限元模型的构建

目的建立包含eBrace托槽、牙、牙周膜、牙槽骨、弓丝和微种植体在内的三维有限元模型,为分析个体化舌侧矫治器上颌腭部不同位置微种植体滑动法关闭上前牙间隙的生物力学特征做准备。方法依据eBrace个体化舌侧矫治器的设计特点,基于CT采集的实际数据,先建立实体模型,再构建含有牙、牙周膜、牙槽骨、托槽、弓丝和微种植体6个成分的个体化舌侧矫治系统的三维有限元模型。结果1．根据微种植体植入位置不同,共建立6个有限元模型,微种植体分别位于上颌第二双尖牙和第一磨牙间、第一磨牙和第二磨牙间距离牙槽嵴顶2mm、6mm和10mm。每个模型包括40个实体模型。2．用10节点四面体单元进行单元剖分,第一个模型（微种植体在上颌第二双尖牙和第一磨牙之间距离牙槽嵴顶2mm）在网格剖分后有节点741670个,单元513925个。其他模型的节点数和单元数类似。结论建立了包含eBrace托槽、牙、牙周膜、牙槽骨、弓丝和微种植体在内的三维有限元模型,该有限元模型构建全面、复杂、真实,几何相似性很强;为下一步分析个体化舌侧矫治器上颌腭部不同位置微种植体滑动法关闭上前牙间隙的生物力学特征奠定了基础。     

安氏Ⅱ类错牙合切牙区牙颌代偿及牙槽骨形态的研究

目的:通过对矫治前安氏Ⅱ类年轻成人错牙合患者进行头影测量分析,观察其切牙区牙颌代偿情况及牙槽骨形态。方法:选取未经治疗安氏Ⅱ类错牙合患者117例,根据上颌中切牙的唇倾程度及垂直骨面型进行分组,通过头影测量分析及t检验对其牙颌代偿情况及牙槽骨形态进行研究。结果:1比较安氏Ⅱ类1分类和2分类错牙合,安氏Ⅱ类1分类者U1/SN、LI/MP、UA、Uap、LAH、LBH和LLH的测量值均大于安氏Ⅱ类2分类患者,但SN/OP、U1/L1、UAH、UDH、UBH、UP、LP、LAP则小于安氏Ⅱ类2分类患者,差异具有显著统计学意义。2不同垂直骨面型间相互比较:均角组和低角组SNA、SNB、L1/MP、UP、UAP、LA、LP、LAP值都显著大于高角组,而ANB、SN/OP、SN/MP、FH/MP、UAH则显著小于高角组。而UDH,LDH,LAH,LBH值则仅均角组显著低于高角组。结论:安氏Ⅱ类1分类错牙合和2分类错牙合相比较,二者在牙颌代偿及牙槽骨形态上均存在显著差异。并且牙颌代偿和牙槽骨形态均受到垂直骨面型的影响。     

一种适用于口腔三维建模的层析测量法的可靠性研究

目的　应用改进的层析测量法进行无牙颌的三维建模,并对其建模精度进行分析研究。方法　采用改进 的层析测量系统对无牙颌模型逐层切削,进行数据运算,重建无牙颌数字模型。用该方法对10个立方体模型分别 重建数字模型,测量建模前后各条边长的数据,对测量结果进行统计分析。结果　对无牙颌模型逐层切削后获得 完整无牙颌数字模型;10个立方体建模前后的总体误差间无显著性差异(P>0·05);在水平方向建模前后的测量数 据间无显著性差异(P>0·05);在高度方向建模前后的测量数据间存在显著性差异(P<0·01),建模后的小于建模 前(0·09±0·08)mm。结论　改进的层析测量法能够适用于口腔高精度的三维建模。     

Finite element modeling of the periodontal ligament under a realistic kinetic loading of the jaw system

PurposeThe stresses and deformations in the periodontal ligament (PDL) under the realistic kinetic loading of the jaw system, i.e., chewing, are difficult to be determined numerically as the mechanical properties of the PDL is variably present in different finite element (FE) models. This study was aimed to conduct a dynamic finite element (FE) simulation to investigate the role of the PDL (PDL) material models in the induced stresses and deformations using a simplified patient-specific FE model of a human jaw system.MethodsTo do that, a realistic kinetic loading of chewing was applied to the incisor point, contralateral, and ipsilateral condyles, through the experimentally proven trajectory approach. Three different material models, including the elasto-plastic, hyperelastic, and viscoelastic, were assigned to the PDL, and the resulted stresses of the tooth FE model were computed and compared.ResultsThe results revealed the highest von Mises stress of 620.14 kPa and the lowest deformation of 0.16 mm in the PDL when using the hyperelastic model. The concentration of the stress in the elastoplastic and viscoelastic models was in the mid-root and apex of the PDL, while for the hyperelastic model, it was concentrated in the cervical margin. The highest deformation in the PDL regardless of the employed material model was located in the caudal direction of the tooth. The viscoelastic PDL absorbed the transmitted energy from the dentine and led to lower stress in the cancellous bone compared to the elastoplastic and hyperelastic material models.ConclusionThese results have implications not only for understanding the stresses and deformations in the PDL under chewing but also for providing comprehensive information for the medical and biomechanical experts in regard of the role of the material models being used to address the mechanical behavior of the PDL in other components of the tooth.     

牙列缺损分类和设计教学软件的研制

目的研制"牙列缺损分类和设计"的教学软件供课堂教学使用.方法利用牙颌组织及修复体三维几何学模型库,采用知识库结构,建立、储存牙列缺损模型及可摘局部义齿模型,并通过软件界面进行交流.结果软件分成教学、测试和维护3个模块,知识库包括了50种常见的牙列缺损状态和近30种可摘局部义齿设计方案.结论本软件有简洁的界面及合理的结构,它的各项功能可以在课堂教学中应用,有利于提高教学质量.     

A novel method of removing artifacts because of metallic dental restorations in 3-D CT images of jaw bone

CT images, especially in a three-dimensional (3-D) mode, give valuable information for oral implant surgery. However, image quality is often severely compromised by artifacts originating from metallic dental restorations, and an effective solution for artifacts is being sought. This study attempts to substitute the damaged areas of the jaw bone images with dental cast model images obtained by CT. The position of the dental cast images was registered to that of the jaw bone images using a devised interface that is composed of an occlusal bite made of self-curing acrylic resin and a marker plate made of gypsum. The patient adapted this interface, and CT images of the stomatognathic system were filmed. On the other hand, this interface was placed between the upper and lower cast models and filmed by CT together with the cast models. The position of the marker plate imaged with the dental casts was registered to those adapted by the patient. The error of registration was examined to be 0.25 mm, which was satisfactory for clinical application. The damaged region in the cranial bone images as an obstacle for implant surgery was removed and substituted with the trimmed images of the dental cast. In the method developed here, the images around the metallic compounds severely damaged by artifacts were successfully reconstructed, and the stomatognathic system images became clear, and this is useful for implant surgery.     

Investigation of cervical muscle mechanisms during jaw movement--using a prototype head-jaw-neck model--

To explain the pain and dysfunction of neck during jaw movement associated with malocclusion, the physiologic relationships between jaw and cervical movement should be understood. However the complicated reflex effects made it difficult to investigate the biomechanical relationship between the head-neck components. For this reason we have created a model for mechanical system dynamic analysis of the normal stomatognathic system to assess the biomechanics of the cervical movement and muscle activity during jaw movement. We have also statistically validated the model and quantitatively verified the model to the human subject by the amounts and conditions of cervical muscle activity. During jaw opening-closing phases the movement of the model was highly correlated to the subject with an identical movement. However low consistency was achieved during intercuspid phase. These findings indicate the establishment of a valid system, which can be used to evaluate the biomechanical relationships between jaw and cervical movement. Moreover the model verification of cervical muscle activity indicate the mechanical action of jaw can be the primary factor to modify cervical muscles, and cervical muscles coordinate to resist changes in head balance during jaw movement to maintains head posture.     

Occlusion as the cause of undiagnosed pain

The teeth provide precise skeleto-motor influences for the stomatognathic system. This unique guidance mechanism characterizes each individual's chewing pattern. It controls the activity of jaw muscles to ensure that appropriate tooth contacts within the limits of existing tooth relationships occur at the end of each chewing cycle. This acts as a means of re-setting the neuromuscular system in anticipation of the next jaw opening movement. The absence of stable centric occlusion at the end point of each chewing cycle alters neuromuscular co-ordination and predisposes to muscle dysfunction. Tooth and jaw or craniomandibular relationships are associated with craniocervical relationships and especially tongue posture. This is also directly influenced by the need for airway maintenance as the predominant influence on tongue-muscle function. The susceptibility to pain and dysfunction is further influenced by individual stereognathic sensitivity or the variable awareness of tooth contour and tooth contacts. These special features are present within the framework of the psycho-physiological and psycho-social significance of the face and mouth, which directly bears on the individual response to and appreciation of pain and dysfunction. Tooth guidance also influences condyle-disc function. Anterior and posterior teeth provide primary and secondary lateral guidance in function, directing the jaw into centric occlusion. If this guidance tends to direct the jaw posteriorly along distal, rather than mesial tooth inclines, it restricts the antero-posterior 'function' of jaw movement at tooth contact. This predisposes to condyle-disc dysfunction and the development of internal derangements, by increasing the likelihood of the posterior thick band of the disc being displaced anteriorly and the condyle posteriorly.(ABSTRACT TRUNCATED AT 250 WORDS)     

Biomechanical finite-element investigation of the position of the centre of resistance of the upper incisors

The position of the centre of resistance (CR) is an essential parameter regarding the planning of orthodontic tooth movements. In the present investigation, the combined CR of the upper four incisors was determined numerically using the finite-element (FE) method. Based on a commercially available three-dimensional data set of a maxilla, including all 16 teeth, as well as known and earlier determined material parameters, FE models of the upper incisors and their surrounding tooth-supporting structures were generated. In the FE system, the model of the anterior segment was loaded with torques of 10 Nmm each at the lateral incisors. The FE model indicated that the individual incisors moved independently, although they were blocked with a steel wire of dimension 0.46 x 0.65 mm(2). The individual CRs were located at 5 mm distal and 9 and 12 mm apical to the centre of the lateral brackets. Thus, the classical view of a combined CR for the anterior segment was disproved and the planning of orthodontic tooth movements of the upper incisors should no longer be based on that concept.     

Four-dimensional visualization of mandibular movement using an individual''s head model reconstructed from cephalograms

We introduce a new four-dimensional (4D) visualizing system of stomatognathic function that combines an individual's 3D head model, reconstructed from cephalograms, and mandibular movement data recorded with a six degrees-of-freedom jaw movement analyzer. The individual's head model was constructed by transforming a standard head model according to the 3D coordinate values calculated from the individual's cephalograms. The accuracy of the 3D reconstructed head model was determined. The error averaged 1.02%, with a range of 0.39–1.58%, and the accuracy was sufficient for clinical use. This method performs dynamic and precise simulation of mandibular movement. We believe that our system will be useful for evaluating the functional background of patients with malocclusions and maxillofacial deformities.