【作者】 严斌；

【导师】 王林；

【作者基本信息】 南京医科大学 ， 口腔临床医学， 2010， 博士

【摘要】 上颌尖牙埋伏阻生是指上尖牙在正常萌出期间,因为颌骨、邻牙或纤维组织阻挡埋伏于粘膜或骨内,而不能萌出到牙弓中正常位置。其对患者口腔正常功能和美观有较大影响,是正畸临床疑难病症之一。以往国内外学者的研究多集中在上颌埋伏尖牙的定位诊断和治疗方法上,对正畸治疗过程中埋伏尖牙移动的生物力学机制认识并不清楚。本研究将影像工程、非线性有限元分析和实验力学技术紧密结合,旨在实现对上颌埋伏尖牙正畸牵引过程的动态仿真和生物力学的量化研究,以建立上颌尖牙埋伏的生物力学分型系统,用于指导临床对埋伏尖牙的精确诊断和个体化矫治器的开发。研究方法第一部分:对102例上颌尖牙埋伏患者牙颌螺旋CT扫描数据采用表面遮盖成像的三维重建方法,展现各埋伏尖牙及邻近结构的形态、大小和位置。在此基础上,通过对121颗上颌埋伏尖牙与邻牙之间三维位置关系的统计分析,建立适合上颌埋伏尖牙的CT影像分型。再将所有上颌尖牙阻生患者,分为42名腭侧阻生组和60名唇侧阻生组。选择年龄、性别匹配,上颌尖牙正常萌出的50名患者作为对照组。应用MIMICS软件完成牙颌三维CT影像测量,获得所有患者的上前牙宽度、牙弓宽度及颌骨宽度等形态学数据,并进行统计学分析。第二部分:选取2例不同类型的上颌尖牙埋伏患者,以其CT数据为基础,利用逆向工程、快速成型等技术来建立包括牙颌组织及矫治器的仿真模型。在前期研究基础上,采用一种超弹模型作为牙周膜材料的非线性本构模型。在不同CT影像分型的上颌埋伏尖牙三维有限元模型上,自不同方向分别加载力值为60g、75g、100g、120g、150g的牵引力,应用ABAQUS软件分析其牙周膜应力分布的量化改变,统计归纳各自的生物力学特点,并通过相移电子散斑干涉技术进行验证,为建立适合不同上颌尖牙埋伏情况的生物力学分型提供理论依据。第三部分:利用三维影像导航技术研究开发适合埋伏牙开窗手术的计算机辅助导航定位系统,并对系统精度进行测试。依据不同生物力学分型的上颌埋伏尖牙在正畸牵引过程中的生物力学特点,建立埋伏尖牙矫治难度评估体系,并对现有埋伏牙正畸牵引固定矫治器的结构进行优化和改良,设计一种具有局部调节能力的矫治器方案。研究结果1、建立了上颌埋伏尖牙CT影像分型数据库并对不同类型上颌尖牙埋伏患者牙颌形态进行了分析,结果显示唇侧阻生患者的所有前牙宽度大于对照组和腭侧组,均有统计学差异;腭侧尖牙阻生患者的中切牙及侧切牙宽度小于正常对照组,有统计学差异,但腭侧尖牙阻生患者的尖牙宽度与对照组比较,无显著性差异;唇、腭侧尖牙阻生患者的第一双尖牙区牙弓宽度都小于对照组,均有显著性差异,但唇、腭侧两组间比较,无统计学差异;三组患者的第一磨牙区牙弓宽度、鼻腔宽度、上下颌骨宽度及两者差值和比例相互之间均无统计学差异。2、应用CT扫描和逆向工程技术建立了包括上颌牙列、牙周膜、牙槽骨及矫治器的高精度非线性三维有限元模型。结合非线性有限元分析法和相移电子散斑干涉实验用于研究不同类型上颌埋伏尖牙在牵引力作用下的牙周组织应力应变。两者的分析结果经比较基本一致,说明该有限元分析方法是可靠的。3、非线性有限元分析结果显示:不同大小载荷下,均表现为上颌埋伏尖牙牙体长轴与正畸力牵引方向的夹角越小,埋伏牙牙周膜应力分布越平均,越易于被牵出;越大则牙周膜应力分布越集中,越不利于被牵出。以此为主要依据创建了上颌尖牙埋伏的生物力学分型及其矫治难度评估体系。4、设计了一种新的埋伏牙定位方法和埋伏牙立体定位专用装置,并自主开发了一套适合口腔科使用的手术导航软件,系统测试结果表明可用于指导埋伏牙开窗手术的精确定位。5、提出了由可旋转式托槽和悬臂梁式加力装置组成的新型埋伏尖牙个体化牵引矫治器设计方案。结论1、首次应用CT三维重建影像测量分析上颌尖牙埋伏患者的牙颌形态特点,揭示了上颌尖牙唇侧和腭侧阻生患者的牙颌形态学特征存在差异,上颌侧切牙宽度和第一双尖牙区牙弓宽度的变化与上尖牙埋伏位置高度相关。2、以牙颌CT影像和逆向工程建模为基础,选用非线性牙周膜本构模型进行三维有限元计算并应用相移电子散斑干涉技术验证结果的方法是切实可行的,能较好用于上颌埋伏尖牙正畸移动的生物力学分析。3、上颌埋伏尖牙与邻牙的三维空间位置关系决定其受相同大小方向正畸牵引力下牙周膜应力分布的特征。埋伏尖牙的方位越有利于其牙体长轴与临床需要的牵引方向一致,越容易助萌,反之则越困难。4、上颌尖牙埋伏的生物力学分型系统基于三维CT影像和生物力学分析的结果而提出,具有一定的科学理论基础,并且简明、直观,对上颌埋伏尖牙的诊断和治疗有重要的指导意义。5、上颌埋伏尖牙三维影像导航定位系统、矫治难度评估体系和个体化矫治器系统的联合运用,有助于实现埋伏尖牙的个性化诊疗,因此具有良好的临床应用前景。更多还原

【Abstract】 Maxillary canine impaction is a condition in which a canine is embedded in the maxillary alveolus so that its eruption is prevented or the tooth is locked in position by bone or by the adjacent teeth. The impacted canine affects the function and aesthetic of oral cavity.The treatment is usually a challenge to orthodontists. The research in existence about the impacted canine mostly focus on the orientation of impacted tooth and the treatment.But biomechanical mechanism on traction of impacted canine is not clear . In order to realize dynamic simulation and biomechanical quantization of the process during traction of impacted canine, imaging engineering method, nonlinear finite element method, and experimental mechanics method were used to inquire this problem. The aim of this study was to establish a biomechanical classification system for maxillary canine impactions. The classification system will guide the precise diagnosis and development of individualized orthodontic appliance for impacted canines.Methods:Part I: To show the 3D shape, size and position of the displaced canines, Surface Shaded Display method was used to reconstruct the dentomaxillofacial CT data of 102 patients with maxillary impacted canines. Based on the analysis of 121 impacted canines’ spatial relationship to adjacent teeth, a 3D CT image classification system for maxillary canine impactions was established. Patients with impaction of maxillary canines were divided into two groups. 42 patients were in palatal group and 60 patients in labial group. The control group comprised 50 untreated patients who were matched for age and sex exhibiting normally erupted and undisplaced maxillary canines. MIMICS software was used to measure the 3D CT images of jaw and teeth. The maxillary anterior teeth size, maxillary arch and jaw width were measured and analyzed statistically among the three groups.Part II: Based on the CT data of 2 patients with different maxillary impacted canines, the dummy model of maxillary dentition, periodontal tissue and Edgewise appliance were set up by reverse engineering software and the rapid prototyping technology. A hyperelastic model was applied to build the nonlinear constitutive model of periodontal ligament.Forces of 60g, 75g, 100g, 120g and 150g were exerted to the finite element models of different impacted canines from different driections. ABAQUS software was use to analyze stress changes of their periodontal ligament. The results of the simulations were tested by experiments of digital speckle pattern interferometry.Part III: A computer-assisted surgical navigation system for exposure of impacted teeth was developed by using 3D image guided technology, and an accuracy test was performed. According to biomechanical characteristics in the procedure of impacted maxillary canine movements produced by orthodontic load, a evaluating criterion for difficulty in therapy was established and a set of individualized orthodontic appliance for repositioning of impacted maxillary canines was designed by using computer-aided technology.Results:1. A database for 3D CT image of different maxillary canine impactions was established. In this database, all anterior teeth size of the labial group was the largest in three groups. In the palatal group, the central and lateral incisors were significantly narrower than that of controls but the size of canine showed no was significantly smaller in patients with impacted canines compared to the control group. The width of arch between 1st molar and jaw was almost normal in three groups.2. Three-dimensional finite element model of maxillary dentition, periodontal ligament, alveolar bone and Edgewise appliances were set up by CT scanning and reverse engineering technology. Through nonlinear finite element analysis and electronic speckle pattern interferometer to conduct a preliminary verification, the result was similar. That means that the method of finite element analysis was reliable.3. The result of nonlinear finite element analysis showed that when the long axis of the maxillary impacted teeth has angle with the direction of the force, the angle is larger, the maximum stress is larger and the stress distribution concentrates more. The angle between the orientation of the traction and the long axis of the impacted canine is smaller, the stress distribution is more average.According to this result, a novel biomechanical classification system for maxillary canine impactions and evaluation system for difficulty in maxillary impacted canines’therapy were established.4. A novel positioning method and device for impacted teeth was designed. A set of surgical navigation software for department of stomatology was developed and proved to be able to guide the surgical exposure of impacted teeth precisely.5. A design proposal of individualized orthodontic appliance for impacted maxillary canines which is comprised of a rotatable bracket and cantilever beam forcing device was created.Conclusion:1. There is a distinction of dentomaxillofacial morphology between palatal and labial canine impactions. The changes of maxillary lateral incisors and arch width between the 1st premolar showed significant associations with the maxillary canine impaction.2. Based on the CT image and reverse engineering ,the method through nonlinear finite element analysis and electronic speckle pattern interferometer to test is feasible.The model can be used to biomechanics analysis for numerical simulation of different impacted maxillary canine movements produced by orthodontic load.3. The impacted canines’ spatial relationship to adjacent teeth determines the characteristics of stress distribution on periodontal ligament. When the long axis of impacted canine is in line with the desired direction of the force,,there are more advantage to the eruption of the impacted canine.4. The biomechanical classification system for maxillary canine impactions was established based on 3D CT image and results of biomechanical analysis. This concise classification has a basement of science theory. It will play an important role in diagnosis and the treatment of impacted canines in the future.5. Computer-assisted surgical navigation system, difficulty evaluation system and individualized orthodontic appliance will contribute to realize the individualized diagnosis and treatment for impacted maxillary canines, and has good perspective in clinical application.更多还原