修复上颌无牙颌不同种植体位置和数目的应力分析

目的：在前端种植体固定桥和后端冠外弹性附着体义齿联合修复上颌无牙颌的修复设计中，比较不同种植体位置和数目的3个有限元模型的应力分布，选择一种更合理的修复设计。方法：建立4个种植体在双侧侧切牙和尖牙的三维有限元模型Ⅰ，通过局部修改，建立2个种植体在双侧尖牙的模型Ⅱ，4个种植体在双侧尖牙和中切牙的模型Ⅲ。应力垂直加载于上颌右侧第一磨牙，加力300N，用MSC软件进行静态应力分析。结果：模型II中23种植体处的应力大约是模型Ⅰ的3倍。模型Ⅲ的附着体、23种植体和13种植体的应力比模型Ⅰ和模型Ⅱ明显高。然而，模型Ⅲ中21种植体和11种植体的应力比模型Ⅰ中22种植体和12种植体处的应力低。在模型Ⅲ中，4个种植体的应力相差很大。结论：在3个模型中，4个种植体在双侧侧切牙和尖牙的模型Ⅰ在生物力学方面是最合理的。     

附着体应用于单侧上颌骨缺损修复的三维有限元分析

目的:对附着体应用于单侧上颌骨缺损修复进行三维有限元力学分析。方法:利用已有的单侧上颌骨缺损的三维有限元模型,在ANSYS程序中分别设计并建立附着体支架,修复两种不同上颌骨缺损情况的模型(附着体位于中切牙或尖牙近中面),进行三维有限元力学分析。结果:应力集中区均位于健侧腭部基托的近前牙区,健侧后牙受力均匀;附着体位于中切牙近中时,中切牙近中面应力值为1.306MPa,附着体与舌面导板的连接处应力较集中;附着体位于尖牙近中时,尖牙近中面应力值为0.797MPa,应力集中区位于舌面导板的前下方转角区。结论:附着体应用于单侧上颌骨缺损修复,符合生物力学要求,未增加基牙的负荷。对附着体支架的设计,应作进一步研究。     

下颌侧切牙缺失固定桥设计基牙受力情况的实验研究

目的比较双端及单端固定桥修复下颌侧切牙缺失时基牙的受力情况。方法应用ANSYS软件,通过三维有限元法建立4种固定桥模型,分别以中切牙和尖牙、中切牙、尖牙、尖牙和第一前磨牙为基牙模拟下颌侧切牙缺失,分析基牙最大受力部位和大小。结果单端固定桥修复模型中,以中切牙作为单一基牙时,基牙根尖受力值最大;双基牙单端桥基牙根尖受力最小;双端固定桥两基牙根尖受力分布最均匀。结论下颌侧切牙缺失患者以双端固定桥修复时,基牙受力最合理;单基牙单端桥设计,中切牙受力大于尖牙,而双基牙的单端桥修复形式较单基牙理想。     

磁性附着体下颌种植覆盖义齿牙槽骨的三维光弹应力分析

目的：研究磁性附着体下颌种植覆盖义齿在各种咬合状态时下颌牙槽骨的应力分布。方法：选取标准无牙颌模型,在双侧尖牙区植入种植体,连接磁性附着体,翻制下颌环氧树脂模型,制作生物功能性全口义齿,分别在正中、前伸、侧向咬合时加载应力,冻结切片,观测各牙位应力条纹。结果：磁性附着体下颌种植覆盖义齿在正中、侧向、前伸咬合应力加载时种植体周围牙槽骨应力值最大,余留牙槽嵴后牙区所受应力大于前牙区。正中、前伸磨牙区最大应力值出现于颊侧,切牙区最大应力值出现于舌侧。侧向工作侧最大应力值出现于唇颊侧,平衡侧最大应力值出现于舌侧。结论：磁性附着体种植覆盖义齿各向咬合时,应力既分布到种植体,也分布到剩余牙槽嵴,可以明显降低种植体周围骨组织的受力,有利于种植体的健康。     

无托槽隐形矫治器联合微种植体内收并压低上前牙的三维有限元分析

目的 运用三维有限元技术研究无托槽隐形矫治器联合微种植体内收并且压低上前牙时,使用不同方式的微种植体牵引的治疗效果差异。 方法 获取患者上颌骨及牙体等锥形束CT数据,使用Mimics、Geomagic、Solidworks和Ansys软件建立所需要的三维有限元模型以及无托槽隐形矫治器。根据微种植体的设计不同,分为4个实验组。第1组为空白对照组;第2组在上颌双侧第二前磨牙和第一磨牙之间各植入一颗微种植体,在双侧尖牙牙套上沿内收方向加0.98 N的力;第3组在第2组基础上,在中切牙之间植入一颗微种植体加力0.98 N压低上前牙;第4组在第2组基础上,在双侧中切牙和侧切牙之间各植入一颗微种植体加力0.56 N压低上前牙。对各组进行受力分析,比较不同位点植入微种植体牵引加力时前牙转矩的改变、运动趋势以及应力分布。 结果 4组中所有上颌切牙皆表现出内收和压低的趋势,且伴有不同程度的转矩改变。第3组上颌中切牙及侧切牙在矢状向冠根位移差最小,第4组上颌中切牙及侧切牙压低值最大,第2组最大应力集中值最大。 结论 将微种植体植入上颌中切牙之间进行牵引更利于转矩控制;而植入上颌中切牙与侧切牙之间并联合前牙垂直牵引时更利于单纯压低,在一定程度上避免了“过山车”效应。     

口腔生物力学

用CAD软件辅助义齿建立力学分析模型的初步研究，垂直负荷下双种植体固定桥种植体周围骨的应力研究，桩核冠修复材料对牙体应力的影响，牙尖斜度对上颌全口义齿基托应力分布的影响，桩核材料对牙本质应力分布的影响，下颌骨典型牙位圆柱状牙种植体周围骨应力分布的三维有限元分析     

种植全口义齿的三维有限元分析--上部连接设计对应力的影响

目的：分析选用不同上部连接设计时种植全口义齿及其支持组织的应力状况以指导临床设计。方法：用三维有限元法研究螺丝固定结构与球帽附着结构对种植体全口义齿应力状况的影响。结果：采用螺丝固定结构较采用球帽附着结构者,义齿的种植体骨界面应力高出６１％,基托应力高出２１８％,种植体本身应力及人造牙列应力变化不大。结论：球帽附着结构较螺丝固定结构能显著降低种植体骨界面应力和义齿基托应力,利于义齿坚固耐用和支持组织健康。     

杆卡附着体下颌种植覆盖义齿牙槽骨的三维光弹应力分析

目的：研究杆卡附着体下颌种植覆盖义齿在各种咬合状态时下颌牙槽骨的应力分布。方法：制作杆卡附着体下颌种植覆盖义齿光弹模型,采用三维冷冻光弹法分析正中、前伸、侧向咬合状态下种植体周围与余留牙槽嵴的应力。结果：三种咬合状态下,种植体颈部和尖周牙槽骨应力值较大,尖周应力值大于颈部应力值;余留牙槽嵴最大应力值出现在磨牙区。侧向牙合工作侧各牙位切片的最大应力值出现于唇颊侧,平衡侧各牙位切片的最大应力值出现于舌侧;前伸牙合侧切牙区唇侧应力最大,中线区及后牙区应力最大值出现于舌侧。结论：杆卡式种植覆盖义齿在正中、前伸、侧向咬合状态下,种植体周围骨组织应力值较大,不利于种植体的健康,因此应用杆卡式附着体时,可考虑增加种植体,扩大基托面积,依据平衡牙合排牙以分散牙合力。     

骨质量对精密附着体天然牙-种植体联合固定桥的应力影响

目的探讨在应用精密附着体天然牙-种植体联合固定桥修复时,骨质量对两种基牙及其周围支持骨组织的应力影响。方法采用三维有限元分析方法,对不同质量骨组织支持的精密附着体天然牙-种植体固定桥的有限元模型进行计算分析。结果固定桥支持骨组织的质量下降后,各基牙和其周围支持骨组织中的应力值明显增大。结论骨质量与精密附着体天然牙-种植体联合固定桥的应力改变具有密切相关性。     

螺旋压缩成骨器配合牙槽外科减阻快速内收上颌前牙的有限元分析

目的探讨螺旋压缩成骨器对上颌前牙应力分布及位移的影响。方法构建螺旋压缩成骨器配合牙槽外科减阻快速内收上颌前牙三维有限元模型,在对上前牙加载位移0.50mm和0.75mm两种工况下,分析上颌中切牙、侧切牙、尖牙唇腭侧及近远中应力分布及位移。结果两种工况下切牙颈部唇侧位移最大,腭侧应力最大;尖牙颈部近中位移和应力最大,唇侧位移和应力分布最小,两种工况载荷效果总体趋势相同。结论螺旋压缩成骨器两种工况对前牙内收都有影响,中切牙、侧切牙、尖牙的内收趋势明显,中切牙和尖牙有旋转趋势。     

Mechanical analysis of the effects of implant position and abutment height on implant-assisted removable partial dentures

PurposeAn increasing number of clinical reports describe the use of dental implants as abutments in implant-assisted removable partial dentures (IARPD). We used three-dimensional finite element analysis to evaluate IARPD as a unilateral mandibular distal extension denture. Specifically, the mechanical effects of implant position and abutment height on the abutment tooth, denture, and denture-supporting tissue were assessed.MethodsThe models analyzed were defects of the left mandibular second premolar and first and second molars prosthetically treated with an IARPD using one implant for each tooth position. There were two abutment heights: one equal to that of the mucosa and another that was elevated 2 mm above the mucosa. Six models were constructed.ResultsFor mucosal-level abutments, movement of the abutment tooth was lower for implants positioned distal to the abutment tooth than for those positioned medial to the abutment tooth. For elevated abutments, movement of the abutment tooth was lower for implants positioned medial to the abutment tooth than for those positioned distal to the abutment tooth.ConclusionsThe mechanical effects on abutment teeth at the same implant position differed in relation to implant abutment height.     

6颗种植体支持的上颌无牙颌固定义齿应力分布研究

目的:分析种植体位置变化时,6颗种植体支持的上颌无牙颌固定义齿的应力分布.方法:选择一名牙列缺失、牙槽骨中度吸收的志愿者,对其头颅部进行CBCT扫描,并利用一系列计算机软件进行数据转换,完成上颌骨三维实体模型的重建.设计8种不同位置种植体支持的固定义齿,建立8个三维有限元模型,分析种植体、上颌骨和固定义齿的应力分布情况.结果:远中没有悬臂的模型比有悬臂的模型的应力差值小;8种位点设计的模型都是应力集中在磨牙区种植体,种植体的应力集中点都是种植体颈部,且是偏向于颊侧.种植体的应力都是磨牙＞前磨牙＞前牙;在8种位点设计的模型中,种植固定义齿和颌骨位移都是集中在前牙区,种植固定义齿的位移是从前牙区向后牙区逐渐变小;8种模型的种植体应力都表现为以压应力为主.模型Ⅰ种植体(位点13、15、17、23、25、27)分散型排列,避免了远中悬臂的设计,6颗种植体的应力分布最均匀.结论:种植体植入位点于13、15、17、23、25、27,是8种方案中最佳的植入位点方案.     

锥体束CT辅助种植义齿导航系统

目的:研发种植义齿导航系统。方法:通过制作缺失牙位模板义齿初步确定植体的定点和方向。再通过CBCT精确测量,利用模板定位仪精确定位,使植体在颌骨内达到理想定位。结果:统计测量70枚术后种植体,经CBCT冠切、矢切检验,达到理想定位标准者占98.6%。讨论:1、种植体在缺隙的定点和在颌骨内的定位应该符合牙合力传导的规律。植体在颌骨内的方向应与相应义齿牙合力传导方向一致。一般情况下,牙合力传导方向与该自然牙的牙体长轴方向一致。2、在部分病例中,植体在颌骨内的定位受到局部骨质条件的限制。植体的理想定位标准是:依据缺失牙位修复体的功能需求,充分利用缺失牙位局部骨质条件,结合种植体的系统、系列特点,依此确定植体的直径、长度以及植体在颌骨内的方向。3、本导航系统首先以自然牙的牙体长轴方向作为参照制作模板义齿,再以锥体束CT摄影技术进行检验,最后再用模板定位仪进行矫正,确保植体在颌骨内达到理想定位。结论:CBCT辅助种植义齿导航系统操作简便,费用低廉,效果良好,可以推广应用。     

Influence of implant number on the biomechanical behaviour of mandibular implant-retained/supported overdentures: A three-dimensional finite element analysis

Objective

The aim of this study was to evaluate strain distribution in peri-implant bone, stress in the abutments and denture stability of mandibular overdentures anchored by different numbers of implants under different loading conditions, through three-dimensional finite element analysis (3D FEA).

Methods

Four 3D finite element models of mandibular overdentures were established, using between one and four Straumann implants with Locator attachments. Three types of load were applied to the overdenture in each model: 100 N vertical and inclined loads on the left first molar and a 100 N vertical load on the lower incisors. The biomechanical behaviours of peri-implant bone, implants, abutments and overdentures were recorded.

Results

Under vertical load on the lower incisors, the single-implant overdenture rotated over the implant from side to side, and no obvious increase of strain was found in peri-implant bone. Under the same loading conditions, the two-implant-retained overdenture showed more apparent rotation around the fulcrum line passing through the two implants, and the maximum equivalent stress in the abutments was higher than in the other models. In the three-implant-supported overdenture, no strain concentration was found in cortical bone around the middle implant under three loading conditions.

Conclusions and clinical significance

Single-implant-retained mandibular overdentures do not show damaging strain concentration in the bone around the only implant and may be a cost-effective treatment option for edentulous patients. A third implant can be placed between the original two when patients rehabilitated by two-implant overdentures report constant and obvious denture rotation around the fulcrum line.     

Prosthetically driven, computer-guided implant planning for the edentulous maxilla: a model study

Objectives: To analyze computer‐assisted diagnostics and virtual implant planning and to evaluate the indication for template‐guided flapless surgery and immediate loading in the rehabilitation of the edentulous maxilla. Materials and Methods: Forty patients with an edentulous maxilla were selected for this study. The three‐dimensional analysis and virtual implant planning was performed with the NobelGuide? software program (Nobel Biocare, Göteborg, Sweden). Prior to the computer tomography aesthetics and functional aspects were checked clinically. Either a well‐fitting denture or an optimized prosthetic setup was used and then converted to a radiographic template. This allowed for a computer‐guided analysis of the jaw together with the prosthesis. Accordingly, the best implant position was determined in relation to the bone structure and prospective tooth position. For all jaws, the hypothetical indication for (1) four implants with a bar overdenture and (2) six implants with a simple fixed prosthesis were planned. The planning of the optimized implant position was then analyzed as follows: the number of implants was calculated that could be placed in sufficient quantity of bone. Additional surgical procedures (guided bone regeneration, sinus floor elevation) that would be necessary due the reduced bone quality and quantity were identified. The indication of template‐guided, flapless surgery or an immediate loaded protocol was evaluated. Results: Model (a) – bar overdentures: for 28 patients (70%), all four implants could be placed in sufficient bone (total 112 implants). Thus, a full, flapless procedure could be suggested. For six patients (15%), sufficient bone was not available for any of their planned implants. The remaining six patients had exhibited a combination of sufficient or insufficient bone. Model (b) – simple fixed prosthesis: for 12 patients (30%), all six implants could be placed in sufficient bone (total 72 implants). Thus, a full, flapless procedure could be suggested. For seven patients (17%), sufficient bone was not available for any of their planned implants. The remaining 21 patients had exhibited a combination of sufficient or insufficient bone. Discussion: In the maxilla, advanced atrophy is often observed, and implant placement becomes difficult or impossible. Thus, flapless surgery or an immediate loading protocol can be performed just in a selected number of patients. Nevertheless, the use of a computer program for prosthetically driven implant planning is highly efficient and safe. The three‐dimensional view of the maxilla allows the determination of the best implant position, the optimization of the implant axis, and the definition of the best surgical and prosthetic solution for the patient. Thus, a protocol that combines a computer‐guided technique with conventional surgical procedures becomes a promising option, which needs to be further evaluated and improved.     

BIOMECHANICAL ANALYSIS OF THE STRESSES GENERATED BY DIFFERENT DISOCCLUSION PATTERNS IN AN IMPLANT-SUPPORTED MANDIBULAR COMPLETE DENTURE

Objectives:

This study evaluated by three-dimensional finite element analysis the tensions generated by different disocclusion patterns (canine guide and bilateral balanced occlusion) in an implant-supported mandibular complete denture.

Material and Methods:

A three-dimensional model of implant-supported mandibular complete denture was fabricated according to the Brånemark protocol. A 5-element 3.75 x 13-mm screw-shape dental implant system was modeled for this study. The implants were located in the intermental foramen region with 3-mm-high prosthetic components joined by a nickel-chromium framework with 12-mm bilateral cantilever covered by acrylic resin and 12 acrylic denture teeth. SolidWorks^® software was used before and after processing the simulations. The mechanical properties of the components were inserted in the model and a 15 N load was established in fixed points, in each one of the simulations. Data were collected in the entire nickel-chromium framework. The results were displayed three-dimensionally as color graphic scales.

Results:

The canine guide generated greater tensions in the region of the first implant, while the bilateral balanced occlusion generated great tensions in the entire metallic framework. The maximum tension found in the simulation of the bilateral balanced occlusion was 3.22 fold higher than the one found in the simulation of the disocclusion in canine guide.

Conclusion:

The pattern of disocclusion in canine guide is the ideal for implant-supported mandibular complete denture.     

The biomechanical analysis of relative position between implant and alveolar bone: finite element method

Background: The purpose of this study is to analyze biomechanical interactions in the alveolar bone surrounding implants with smaller‐diameter abutments by changing position of the fixture–abutment interface, loading direction, and thickness of cortical bone using the finite element method. Methods: Twenty different finite element models including four types of cortical bone thickness (0.5, 1, 1.5, and 2 mm) and five implant positions relative to bone crest (subcrestal 1, implant shoulder 1 mm below bone crest; subcrestal 0.5, implant shoulder 0.5 mm below bone crest; at crestal implant shoulder even with bone crest; supracrestal 0.5, implant shoulder 0.5 mm above bone crest; and supracrestal 1, implant shoulder 1 mm above bone crest) were analyzed. All models were simulated under two different loading angles (0 and 45 degrees) relative to the long axis of the implant, respectively. The three factors of implant position, loading type, and thickness of cortical bone were computed for all models. Results: The results revealed that loading type and implant position were the main factors affecting the stress distribution in bone. The stress values of implants in the supracrestal 1 position were higher than all other implant positions. Additionally, compared with models under axial load, the stress values of models under off‐axis load increased significantly. Conclusions: Both loading type and implant position were crucial for stress distribution in bone. The supracrestal 1 implant position may not be ideal to avoid overloading the alveolar bone surrounding implants.     

Initial stress differences between sliding and sectional mechanics with an endosseous implant as anchorage: a 3-dimensional finite element analysis

Endosseous implants have been used as orthodontic anchorage in recent years. A 3-dimensional mathematical model was constructed that uses the finite element method, which simulated an endosseous implant and an upper canine with its periodontal ligament and cortical and cancellous bone. Levels of initial stress were measured during 2 types of canine retraction mechanics (friction and frictionless). The lower magnitude and more uniform stresses in the implant and its cortical bone were found to have a moment-force ratio (M/F) of 6.1:1, whereas the canine and its supporting structures exerted a M/F ratio of 10.3:1. On the basis of these results, when the anchor unit is an endosseous implant, it seems better to use a precalibrated retraction system without friction (T-loop) where a low load-deflection curve would be generated.