Finite element analysis of the dental implant using a topology optimization method

In recent years, many attempts have been made to optimize the shape of dental implants. The purpose of this study took advantage of the topology optimization in the finite element (FE) method to look for redundant material distribution on a dental threaded implant and redesigned a new implant macrogeometry with the evaluation of its biomechanical functions. Three-dimensional FE models were created of a first molar section of the maxilla and embedded with an implant, abutment and a superstructure by using the commercial software ANSYS 11.0. The final design of a new implant was shaped by topology optimization, and four FE models namely traditional implants with bonded (TB) and contact (TC) interfaces, and new implants with bonded (NB) and contact (NC) interfaces, were established. Material properties of compact and cancellous bone were modeled as fully orthotropy and transversely isotropy respectively. Oblique (200-N vertical and 40-N horizontal) occlusal loading was applied on the central and distal fossa of the crown. The FE model estimated that the volume of the new implant could be reduced by 17.9% of the traditional one and the biomechanical performances were similar, such as the stress of the implant, stress of the implant-bone complex, lower displacement, and greater stiffness than the traditional implant. The advantages of the new implant increased the space to allow more new bone ingrowth or assist in fusing more bone graft into the bone sustaining the implant stability and saved material. Its disadvantage was higher stress level compared with that of the traditional implant.     

基于CT图像种植牙的有限元分析

背景：多层螺旋CT的出现及后处理技术为种植牙手术前模拟测量手术位置、手术区域等建立标准化数值。 目的：评价基于螺旋CT图像的有限元分析在种植牙中的研究和临床价值。 方法：以“CT,有限元,种植牙,受力分析”为中文关键词;以“CT,finite element, dental implants,stress analysis ”为英文关键词,采用计算机检索2002年1月至2012年1月相关文章。纳入与种植牙有限元分析相关文章;排除重复研究或Meta分析类文章。以7篇文献为重点讨论有限元分析在种植牙中的研究和应用。 结果与结论：螺旋CT采集的颌骨DICM图像经过建模后进行的有限元分析,为手术前提供更全面、更可靠的影像资料,临床口腔医师可根据有限元模型进行手术方案设计,测量手术中需要的数据,模拟手术流程,减少了患者的痛苦。把CT和数字化的模型建立及有限元分析的生物力学研究合理的结合,分析需要种植牙的位置和与周围结构关系,为口腔临床医师提供全面的影像资料和力学分析依据。     

A clinical case report: interface analysis of a successful well-functioning transmandibular implant from a cadaver mandible

Transmandibular implants (TMI) are indicated both for functional reconstruction of the severely atrophic mandible and when routine augmentation is unpredictable. This study investigates the interface of bone around a TMI, retrieved from the cadaver. The TMI had successfully functioned for 7 years. The mandible was immersed in 10% formaldehyde and sectioned into nine appropriate pieces. Samples were embedded in polymethylmethacrylate, and cut around the transosseous posts and cortical screws in both vertical and horizontal sections. Samples were analyzed at 400 MHz (nominal lateral resolution, 2.5 microm) using a UH3 Scanning Acoustic Microscope (Olympus, Tokyo, Japan). The middle of implant specimens 1-4 were cut to 50 microm, and stained by toluidine blue for light microscopy. Dental X-rays showed no bone resorption around any implant. On a 2-mm lateral scan, almost uniform interface space was seen between bone and implant surface in cortical screws. There are wider spaces around the transmandibular posts in the superior area. Histology revealed the small area of direct contact. There is bone marrow space in the interface, with no significant fibrous tissue. We interpret these results at the interface to be because of adaptation for stress distribution.     

包含种植体下颌骨颏部受力的有限元分析

目的　通过对右侧下颌第1磨牙为种植牙的下颌骨,颏部给予100 N水平力作用的有限元分析,揭示种植体对下颌骨应力传导的影响。 方法　利用CT图像,建立缺失第1磨牙的下颌骨和种植牙的三维有限元模型,保持下颌骨的边界约束,给予颏部100 N的水平外力作用,分析下颌第1磨牙种植牙区域应力变化和整体下颌骨的应力变化。 结果　颏部受到水平外力100 N作用后,右侧第1磨牙种植区域断面应力变化：10.37 mm与86.38 mm位置出现应力最低,其最大应力峰值分别为9.005 Pa、9.067 Pa;52.97 mm位置处出现应力最大,应力的峰值94.962 Pa。左侧第1磨牙断面应力变化：10.82 mm与83.82 mm位置出现应力最低,其最大应力峰值分别为18.227 Pa、8.867 Pa;54.66 mm位置处出现应力最大,应力的峰值93.912 Pa。下颌骨的整体应力变化：颏部受力部位最大,最大的应力峰值为260.524 Pa。 结论　一定条件下第1磨牙位置的种植体植入不影响下颌骨的正常下颌骨的应力传导。     

Finite element analysis of the effects of a floating mass transducer on the performance of a middle ear implant

Experimental evidence has shown that floating mass transducers (FMTs) play a key role in the performance of middle ear implants. However, because of the tiny size and complex structure of the middle ear, systematic experimental study of the influences of FMTs is difficult to carry out. In this paper we develop a FMT-attached middle-ear finite element model to investigate some effects of a FMT on the performance of a middle ear implant. This model was constructed based on a complete set of computerized tomography section images of a healthy volunteer's left ear. The validity of the developed model was verified by comparing the model-predicted motion of the tympanic membrane and stapes footplate with published experimental data. The result shows that the FMT produces a mass loading effect prominently at high frequencies, the force required to drive the incus to the equivalent of 100 dB sound pressure level (SPL) is about 89?μN, and setting the attachment position of the FMT close to the incudostapedial joint can enhance the driving effect.     

Finite element analysis of the influence of different implant designs on the stress of mandibular edentulous jaw

BACKGROUND: The implant fixed complete denture for mandibular edentulous jaws has become one of the main clinical restoration methods. Mechanical studies on different implant designs can help clinical selection of implant designs in line with biomechanical principles, which is beneficial to maintain the long-term stability of implant dentures. OBJECTIVE: To establish the models for the distribution of different implant sites with the same cantilever length, and to analyze the influence of implant sites, the symmetry of implant distribution and the number of implants on the stress distribution around the abutment, implant, and bone tissue. METHODS: Cone beam CT data of an edentulous mandible were selected. The cone beam CT data, implant, abutment, and crown restoration data were used to create finite element model of different transplantation sites and regions, and different number of implants. The premolars and molars regions were bilaterally subjected to a vertical load of 150 N. The software was used to calculate the stress of the abutment, implant, and bone tissue, and then statistical analysis was performed. RESULTS AND CONCLUSION: (1) When the frontmost implant was closer to the front, the stress on the abutment, implant and bone tissue would gradually decrease. For four implants, when the number of implants located at and before the lateral incisor was 2, the bone tissue stress value was the smallest, and there was a statistical difference in the stress value with 1 and 0 implants (P < 0.05). For five implants, when the frontmost implant site was located at and before the lateral incisor, there was a statistical difference in the stress value with the canine and later (P < 0.05). Therefore, when the length of the cantilever was fixed (10 mm in the experiment), the foremost implant of 4 or 5 implants should be placed in the lateral incisor and the front site. When there were four implants, the number 2 of implants before the lateral incisor was a better choice (2) When the cantilever length and anterior-posterior spread (the distance between the frontmost implant and the two farthest implants) remained unchanged. The symmetry of the model had no statistical difference in the stress distribution around the abutment, implant and bone tissue (P > 0.05). Therefore, the implants were not arranged in accordance with the principle of symmetry when the cantilever length and anterior-posterior spread remained unchanged. (3) When the number of implants was four, the stress around abutment and implant was significantly larger, and the difference in stress was statistically significant with five and six implants (P < 0.05). Therefore, five or more implants are better for the implant fixed complete denture. © 2022, Publishing House of Chinese Journal of Tissue Engineering Research. All rights reserved.     

Finite element analysis of bioelectric phenomena

This article reviews the application of finite element methods to models of bioelectric phenomena. The models represent the electrical fields created in the body as a result of membrane current sources or external current applied for diagnostic or therapeutic purposes. We formulate the governing equations for these models and then derive the finite element equations for the generalized bioelectric problem. The 32 papers reviewed here, all those appearing in the literature to date, cover the areas of electrocardiology, therapeutic and functional electrical stimulation in the cerebellum, cochlea, spinal cord, and peripheral nerves, cardiac defibrillation, electrical impedance tomography, bidomain cardiac models, electroporation, and therapeutic electrical stimulation of bone. For each, we summarize the purpose of the study, the model details and assumptions, the major results, and the applicability of the study. The models are then considered as a group to critique the appropriateness of the finite element method, the means of implementation, and the factors affecting accuracy, thus providing an overview of the state of finite element modeling of bioelectric phenomena.     

有限元分析全膝关节置换股骨假体置入定位参数及临床优化验证

文章快速阅读：  文题释义：全膝关节置换三维有限元仿真模型：是指对股骨假体截骨定位参数进行正交实验,选择股骨假体的平移量、外旋度数、外翻度数3个参数作为正交实验的相关因素,创建全膝关节置换膝关节的有限元模型。活动平台型膝关节假体：其聚乙烯衬垫与托盘不固定,之间能够自由滑动和旋转,可以减少聚乙烯磨损和假体松动的风险,现阶段临床应用比较多的是活动性膝关节假体,该假体能够扩大相应界面与聚乙烯衬垫的接触面积,减少接触应力。   背景：三维有限元仿真分析在生物力学中有着广泛应用,但在膝关节置换中的研究不多,对股骨假体的研究也比较少。目的：有限元分析膝关节置换股骨假体置入的优化定位参数,并对Gemini-PS膝关节假体全膝关节置换进行临床验证。方法：①构建全膝关节置换膝关节有限元模型,对股骨假体截骨定位参数进行正交实验,选择股骨假体的平移量A、外旋度数B、外翻度数C 3个参数作为正交实验的相关因素,每个参数取3个值建立正交表,创建9个实验组合的全膝关节置换膝关节的有限元模型,对9个模型进行有限元分析,通过优化处理进行方差和极差分析。②纳入42例(47膝)中老年膝骨关节炎患者,采用Gemini-PS 膝关节假体进行全膝关节置换,采用美国特种外科医院膝关节评分及美国膝关节协会评分评价置换前后膝关节功能,以疼痛目测类比评分评估置换前后膝关节疼痛程度。结果与结论：①聚乙烯衬底表面压应力峰值最小的为平移0 mm,外旋3°,外翻6°组合,压应力峰值为15.9 MPa;聚乙烯衬垫表面压应力的影响因素中,内外平移的影响大于外旋角度的影响大于外翻角度的影响;通过极差分析和方差分析发现股骨假体置入的最佳定位参数组合为平移0 mm,外旋3°,外翻6°;通过仿真计算证明正交实验是有效的;②42例患者均得到随访,随访时间12-36个月,1例发生术口下段皮下脂肪液化;置换后末次随访患膝美国特种外科医院膝关节评分及美国膝关节协会评分均较置换前显著提高(P < 0.05);置换后疼痛目测类比评分较置换前显著降低(P < 0.05)。X射线检查未发现骨溶解、假体脱位及松动等并发症,置换后膝关节功能恢复良好;③结果提示,股骨假体置入位置的微小变化都会引起聚乙烯衬垫表面压应力峰值的异常分布,全膝关节置换术中对股骨假体进行准确定位可以取得良好的置换效果。 中国组织工程研究杂志出版内容重点：人工关节;骨植入物;脊柱;骨折;内固定;数字化骨科;组织工程 ORCID:0000-0002-3861-0467(徐高伟)     

Finite element analysis of a Gamma nail within a fractured femur

Failures of Gamma nails which treat unstable femoral fractures have been reported. In this paper, a finite element model to include a Gamma nail within a fractured femur was used to investigate the stresses in the Gamma nail. The effects for different types of fracture were investigated. The results show that its use for subtrochanteric fractures will cause higher stresses at the lag screw and upper distal screw insertion holes in the nail than when used for femur neck fractures.     

Finite element analysis of a four-unit all-ceramic fixed partial denture

All-ceramic restorations are known to be prone to brittle fracture. However, a previously performed in vitro study indicates that four-unit fixed partial dentures (FPDs) with a zirconia framework are sufficiently strong to withstand occlusal forces in the posterior region. The aim of this study was to determine the stress distribution in such a four-unit FPD made of yttria-stabilized polycrystalline tetragonal zirconia (Y-TZP), under an occlusal load. A three-dimensional finite element model was constructed and a stress analysis performed with a force of 1630 N applied at the centre of the middle connector area. The location of maximum tensile stress according to finite element analysis coincided with the fracture origin of all 10 specimens fractured within the previous in vitro study. The maximum tensile stress in the area of the middle connector amounted to 633 MPa. It increased with the load being applied from the oral towards the buccal side (648 MPa) and decreased with the load being applied from the buccal towards the oral side (570 MPa). These stresses are of the same order as the flexural strength of Y-TZP, determined under standardized test conditions to be 600–1000 MPa. The model presented is intended to be used for further investigations, including thermally induced stresses during veneering.     

Finite element analysis in functional morphology

This article reviews the fundamental principles of the finite element method and the three basic steps (model creation, solution, and validation and interpretation) involved in using it to examine structural mechanics. Validation is a critical step in the analysis, without which researchers cannot evaluate the extent to which the model represents or is relevant to the real biological condition. We discuss the method's considerable potential as a tool to test biomechanical hypotheses, and major hurdles involved in doing so reliably, from the perspective of researchers interested in functional morphology and paleontology. We conclude with a case study to illustrate how researchers deal with many of the factors and assumptions involved in finite element analysis.     

Finite element analysis in vertebrate biomechanics

This special issue of The Anatomical Record presents a series of papers that apply the method of finite element analysis (FEA) to questions in vertebrate biomechanics. These papers are salient examples of the use of FEA to test hypotheses regarding structure-function relationships in complexly shaped biological objects such as skulls and in areas of the skeleton that are otherwise impervious to study. FEA is also a powerful tool for studying patterns of stress and strain in fossil animals and artificial constructs hypothesized to represent ancestral conditions. FEA has been used deductively, to study patterns of growth and development, and to investigate whether skull shapes can be created from amorphous blocks using an iterative approach of loading and removing elements. Several of the papers address methodological issues, such as the relative importance of loading conditions and material properties for generating an accurate model and the validation of models using in vivo strain data. Continuing improvements in model building techniques will make possible increased application of FEA to study the functional effects of variation in morphology, whether through ontogenetic or phylogenetic transformations.     

Finite element analysis of unicompartmental knee arthroplasty

Concerns over accelerated damage to the untreated compartment of the knee following unicompartmental knee arthroplasty (UKA), as well as the relatively poor success rates observed for lateral as opposed to the medial arthroplasty, remain issues for attention. Finite element analysis (FEA) was used to assess changes to the kinematics and potential for cartilage damage across the knee joint in response to the implantation of the Oxford Mobile Bearing UKA. FE models of lateral and medial compartment arthroplasty were developed, in addition to a healthy natural knee model, to gauge changes incurred through the arthroplasty. Varus–valgus misalignments were introduced to the femoral components to simulate surgical inaccuracy or over-correction. Boundary conditions from the Stanmore knee simulator during the stance phase of level gait were used. AP translations of the tibia in the medial UKA models were comparable to the behaviour of the natural knee models (±0.6 mm deviation from pre-operative motion). Following lateral UKA, 4.1 mm additional posterior translation of the tibia was recorded than predicted for the natural knee. IE rotations of the medial UKA models were less consistent with the pre-operative knee model than the lateral UKA models (7.7° vs. 3.6° deviation). Varus misalignment of the femoral prosthesis was more influential than valgus for medial UKA kinematics, whereas in lateral UKA, a valgus misalignment of the femoral prosthesis was most influential on the kinematics. Resection of the cartilage in the medial compartment reduced the overall risk of progressive OA in the knee, whereas removing the cartilage from the lateral compartment, and in particular introducing a valgus femoral misalignment, increased the overall risk of progressive OA in the knee. Based on these results, under the conditions tested herein, both medial and lateral UKA can be said to induce kinematics of the knee which could be considered broadly comparable to those of the natural knee, and that even a 10° varus–valgus misalignment of the femoral component may not induce highly irregular kinematics. However, elevated posterior translation of the tibia in lateral UKA and large excursions of the insert may explain the higher incidence of bearing dislocation observed in some clinical studies.     

退变性脊柱侧弯的生物力学有限元分析

背景：脊柱在结构、形状、材料特性以及承受载荷方面都比较复杂,传统的生物力学方法不能完全解决这些特性问题。 目的：探讨退变性脊柱侧弯椎间盘、关节突关节、椎体等的应力分布,为其发生、发展的生物力学机制提供依据。 方法：基于退变性脊柱侧弯患者T₁₂-S₁上段连续的CT扫描图像,赋予模型特定的材料属性,建立完整、有效的退变性脊柱侧弯三维有限元模型。在前屈、后伸、左侧弯、右侧弯、左旋转、右旋转6种工况下对模型进行加载,计算和分析脊柱的活动度、椎间盘、椎体及关节突关节软骨的应力分布。 结果与结论：退变性脊柱侧弯有限元模型比正常腰椎的活动度要小,椎间盘应力分布趋向于椎间盘的四周,后伸运动时各椎间盘应力最大,侧弯顶点椎体容易出现应力集中的情况,在旋转工况下关节突软骨的应力集中最明显,后伸工况下次之,尤其以侧弯顶点节段的关节突软骨影响最大。退变性脊柱侧弯侧弯顶点容易出现应力集中,后伸、旋转运动可加重退变性脊柱侧弯发展。     

距骨缺血性坏死的有限元分析

背景：对距骨缺血性坏死的具体临床治疗,目前仍有很大争议。 目的：观察不同程度距骨坏死时,距骨滑车关节面上的应力及其分布变化。 方法：利用8具踝关节标本建立踝关节三维有限元模型,通过改变各模型距骨坏死的体积分析距骨滑车关节面压应力与其分布的变化规律,计算出距骨缺血性坏死可能诱发踝足创伤性关节炎或出现距骨塌陷的临界坏死体积。 结果与结论：实验成功建立了踝关节三维有限元模型。分析发现距骨内、外侧坏死程度比较小时,距骨滑车关节面应力分布变化不大;当内侧距骨坏死体积达到(26.6±1.5)%,外侧距骨坏死体积达到(35.0±2.5)%时,距骨坏死组织与正常骨组织边界区域出现应力集中的现象,其应力区域呈不规则形,提示,此时诱发踝足创伤性关节炎或发生距骨体塌陷的危险性很高,应手术治疗。     

脊柱侧凸治疗进展中的有限元分析

背景：脊柱侧凸是一种包括椎体水平面旋转的复杂病理特点的三维脊柱畸形。有限元分析法可取代传统的生物力学实验法进行重复实验分析以及数字化仿真模拟,在脊柱侧凸的生物力学研究中的运用日益深入。目的：旨在强调运用有限元分析法对脊柱侧凸的支具和手术治疗方面进行简要的阐述。方法：以“脊柱侧凸;有限元”为检索词,检索PubMed数据库以及万方数据库1986年1月至2013年5月文献。选择文章主要内容与脊柱侧凸治疗的有限元分析直接相关的、代表性好、相关领域权威杂志的文章共38篇进行讨论。结果与结论：如何设计出更加符合脊柱侧凸生物力学特征的个体化支具已成为研究热点。利用多重影像学技术将肋骨、胸骨以及骨盆等引入有限元模型中,分析研究脊柱侧凸施加三维矫形力的最佳方式。研究发现施加载荷最佳的方式是在脊柱侧凸的凸侧区域。有限元分析法可预测和评估患者的矫形过程及效果,进而制定出合理的矫形治疗方案。有限元分析法模拟分析内固定器械与脊柱之间的应力分布情况,更有效的预防治疗后并发症的发生。中国组织工程研究杂志出版内容重点：人工关节;骨植入物;脊柱;骨折;内固定;数字化骨科;组织工程全文链接：     

Finite element application in implant research for treatment of lumbar degenerative disc disease

Surgical treatment for disc degeneration can be roughly grouped as fusion, disc replacement and dynamic stabilization. The clinical efficacy and biomechanical features of the implants used for disc degenerations can be evaluated through short- or long-term follow up observation, in vitro and in vivo experiments and computational simulations. Finite element models are already making an important contribution to our understanding of the spine and its components. Models are being used to reveal the biomechanical function of the spine and its behavior when healthy, diseased or damaged. They are also providing support in the design and application of spinal instrumentation. The article reviewed the most recent studies in the application of FE models that address the issue of implant research for treatment of low back pain. The published studies were grouped and reviewed thoroughly based on the function of implants investigated. The considerations of the finite element analysis in these studies were further discussed.     

Finite element analysis of a glass fibre reinforced composite endodontic post

In this work the mechanical response to external applied loads of a new glass fibre reinforced endodontic post is simulated by finite element (FE) analysis of a bidimensional model. The new post has a cylindrical shape with a smooth conical end in order to adequately fit the root cavity, and to avoid edges that could act as undesired stress concentrators. Mechanical data obtained by three-point bending tests on some prototypes fabricated in the laboratory are presented and used in the FE model. Under various loading conditions, the resulting stress component fields are hence compared with those obtained in the case of two commercial endodontic posts (i.e. a cast metal post and a carbon fibre post) and with the response of a natural tooth. The gold cast post-and-core produces the greatest stress concentration at the post-dentin interface. On the other hand, fibre-reinforced composite posts do present quite high stresses in the cervical region due to their flexibility and also to the presence of a less stiff core material. The glass fibre composite shows the lowest peak stresses inside the root because its stiffness is much similar to dentin. Except for the force concentration at the cervical margin, the glass fibre composite post induces a stress field quite similar to that of the natural tooth.     

Finite element analysis applied to cornea reshaping

A 2-D finite element model of the cornea is developed to simulate corneal reshaping and the resulting deformation induced by refractive surgery. In the numerical simulations, linear and nonlinear elastic models are applied when stiffness inhomogeneities varying with depth are considered. Multiple simulations are created that employ different geometric configurations for the removal of the corneal tissue. Side-by-side comparisons of the different constitutive laws are also performed. To facilitate the comparison, the material property constants are identified from the same experimental data, which are obtained from mechanical tests on corneal strips and membrane inflation experiments. We then validate the resulting models by comparing computed refractive power changes with clinical results. Tissue deformations created by simulated corneal tissue removal using finite elements are consistent with clinically observed postsurgical results. The model developed provides a much more predictable refractive outcome when the stiffness inhomogeneities of the cornea and nonlinearities of the deformations are included in the simulations. Finite element analysis is a useful tool for modeling surgical effects on the cornea and developing a better understanding of the biomechanics of the cornea. The creation of patient-specific simulations would allow surgical outcomes to be predicted based on individualized finite element models.     

Finite element contact analysis of the hip joint

The hip joint plays an important role in the musculoskeletal system; however, current knowledge of the mechanics of the hip joint, especially with regard to the distribution of stress, remains limited. In experimental research, difficulties arise during reproduction of physiological conditions of daily activities and practicable measurement of locations inside the hip joint without violating the physiological environment. On the other hand, numerical approaches, such as finite element analysis, have become useful tools in the field of biomechanics. In finite element contact analysis of the hip joint, due to discretization of contact surfaces, computational instability might occur when the contact nodes move near the edges of the contact elements. In this study, to overcome this problem, a contact smoothing approach was introduced by applying Gregory patches. Contact analysis of the hip joint was then performed for three representative daily activities; i.e., walking, rising up from a chair and knee bending. The effectiveness of the adopted smoothing approach was verified by comparing the results with those obtained experimentally. The distribution and history of contact stress, which have heretofore been scarcely reported, were also obtained and the implications associated with osteoarthritis were discussed.