单端固定式下颌骨修复体的应力分析

目的：针对包括一侧髁状突的下颌骨缺损,通过有限元应力分析,了解单端固定式下颌骨修复体在功能运动时的受力与变形规律,以期寻求更加合理的修复体的设计和固定方式。方法：建立下颌骨断端和修复体的简易三维模型,模拟咀嚼运动,施加垂直方向载荷,进行有限元法应力分析,计算出该模型各组成部分的应力分布和受力变形。结果：在该模型加载时,延伸板基部和近断端处上部的螺钉颈部是应力集中的部位,近断端处下部的螺钉颈部和修复体的远端舌侧为形变最大的部位。结论：单端固定式下颌骨修复体在加载时,延伸板的基部和靠近断端的固定螺钉是应力集中的部位,修复体远离固定的一侧是变形最大的部位,提示我们应将延伸板形态设计为尽可能加宽,并应增加下颌骨下缘处的固定,使修复体与下颌骨断端受力更加合理,变形也尽可能缩小。     

LISS-DF近端螺钉不同固定方式的有限元分析

目的研究LISS-DF治疗股骨远端骨折近端螺钉不同固定方式对应力分布规律的影响,寻找符合生物力学原理的固定方式,为临床应用提供理论依据。方法在ANSYS9.0软件中建立LISS-DF钢板固定股骨远端骨折（AO/OTA33-A3型）的实体模型和有限元模型。在近端螺钉不同单、双皮质固定方式下,通过模拟生理应力做轴向加载实验并进行有限元计算和分析。结果1、3孔单2、4孔双皮质固定时,近端螺钉最大应力值在不同固定方式中最小为24.21975Mpa,位移值为0.131424um与其它固定方式相当且均较小,说明该固定方式可以取得较好的力学效果。结论近端螺钉靠近骨折端处双皮质固定,其余螺钉间隔单双皮质固定时,可以减少应力集中现象,得到更好的把持力,使固定更牢固,从而降低固定失败的风险性。     

人工半骨盆假体置换联合腰椎椎弓根螺钉固定术后生物力学的有限元分析

目的:建立人工半骨盆假体置换与联合腰椎椎弓根螺钉固定后的三维有限元模型,评价腰骶段生物力学改变后半骨盆假体力学结构的特点。方法:采用CT薄层扫描采集原始数据,分别建立正常骨盆、半骨盆假体置换术后以及半骨盆假体置换联合腰椎椎弓根螺钉固定术后骨盆的三维有限元模型,分别在第4腰椎上终板平面施以500 N的垂直纵向载荷,分析不同骨盆模型的应力分布特点。结果:与正常骨盆有限元模型相比,半骨盆假体置换术后健侧骨盆应力分布以骶髂关节、髋臼窝及耻骨为主,置换侧半骨盆假体以耻骨连接棒、髋臼杯及髂骨座为主,最大应力出现在耻骨连接棒,应力峰值为65.62 MPa。联合腰椎椎弓根螺钉固定后健侧应力相对减小,置换侧髂骨固定座与骶骨固定处应力相对减小,应力分布以腰椎椎弓根钉棒、耻骨连接棒及髋臼杯为主,最大应力出现在椎弓根螺钉,应力峰值为107 MPa。结论:半骨盆假体置换联合腰椎椎弓根螺钉固定后钉棒分担了半骨盆置换后健侧骨盆及置换侧髂骨固定座与骶骨固定处附近的部分应力,缓解应力集中现象,降低术后骨盆破坏风险,一定程度上增加了半骨盆置换后骨盆的稳定性。     

LISS钢板治疗股骨远端骨折有限元建模及分析

目的建立LISS-DF治疗股骨远端骨折近端螺钉不同单双皮质固定的三维有限元模型,并进行初步生物力学分析。方法提取CT图片相关数据,利用自行编写程序生成命令流文件,建立完整股骨以及16个不同LISS-DF治疗股骨远端AO分型33-A3型骨折的实体模型（钢板和股骨不接触、螺钉分别固定于钢板和股骨）,进行网格划分。分析不同载荷作用下完整股骨和LISS钢板近端螺钉全双皮质固定治疗骨折的模型受力状况。结果建立了相关的有限元模型。不同载荷作用下,LISS钢板近端螺钉全双皮质固定模型和完整股骨的应力集中均位于股骨颈内侧和股骨干外侧中下1/3处。相同载荷作用下,LISS钢板近端螺钉全双皮质固定模型的股骨颈部最大等效应力值略减小,股骨干最大等效应力值明显减小。结论研究建立的三维有限元模型,为应用LISS治疗股骨骨折的生物力学分析提供了良好的实验平台和基础。从生物力学角度而言,LISS-DF近端螺钉全双皮质固定为治疗股骨远端复杂骨折的有效方法。     

股骨骨折术后1年随访骨愈合模型的有限元分析

目的：对股骨骨折髓内钉术后1年骨愈合模型快速建模,通过有限元分析研究对比术前术后模型,通过术前判定内固定取出后骨折断端是否断裂。方法：运用Mimics、Geomagic Studio、Abaqus等软件采用快速个体化建模方法对股骨骨折髓内钉术后1年内固定取出术前后的多层螺旋CT数据进行快速建立模型,术前模型模拟剥除钢板后进行有限元分析,施加人体单腿站立时的静力载荷和约束,并将分析结果与术后模型进行对比,观察米塞斯应力分布情况、最大值及其所处部位。结果：按照材料属性进行区别显示米赛斯应力的最大值及最小值,在不同应力载荷下,手术前后各类型材料的米赛斯应力最大值及最小值部位相同,各类型材料中,最大值均没有位于骨折断端,不同方法的最大应力值部位相近,均在股骨中远端1/4交界处,手术前后应力分布基本相同。结论：采用个体化建模方法可以对骨折内固定取出前的骨愈合模型进行运算分析,快速预判术后是否导致骨折断端断裂。     

不同材料充填修复下颌第一前磨牙楔状缺损的应力分析

目的研究三种材料对两种角度下颌第一前磨牙楔状缺损的修复效果。方法在下颌第一前磨牙颊颈部深度为1mm,夹角分别为30°、90°的楔状缺损有限元模型上用银汞合金、复合树脂和玻璃离子粘固粉三种材料进行缺损修复,以未修复的楔模型为对照,加载100N轴向力后,利用三维有限元方法进行牙颈部应力分析。结果三种材料修复均改善了缺损牙体的应力集中。银汞合金修复体较其他两种材料承受了更大的应力,使缺损局部牙体应力集中状况得以更多缓解,在角度增加时作用更明显。复合树脂最有效降低牙体内部区域的应力集中。结论楔状缺损充填修复可缓解缺损区牙体硬组织的应力集中,复合树脂相对理想。     

股骨骨折术后1 年随访骨愈合模型的有限元分析

目的：对股骨骨折髓内钉术后1 年骨愈合模型快速建模，通过有限元分析研究对比术前术后模型，通过术前判定内固定取 出后骨折断端是否断裂。方法：运用Mimics、Geomagic Studio、Abaqus等软件采用快速个体化建模方法对股骨骨折髓内钉术后1 年内固定取出术前后的多层螺旋CT 数据进行快速建立模型，术前模型模拟剥除钢板后进行有限元分析，施加人体单腿站立时的 静力载荷和约束，并将分析结果与术后模型进行对比，观察米塞斯应力分布情况、最大值及其所处部位。结果：按照材料属性进行 区别显示米赛斯应力的最大值及最小值，在不同应力载荷下，手术前后各类型材料的米赛斯应力最大值及最小值部位相同，各类 型材料中，最大值均没有位于骨折断端，不同方法的最大应力值部位相近，均在股骨中远端1/4 交界处，手术前后应力分布基本相 同。结论：采用个体化建模方法可以对骨折内固定取出前的骨愈合模型进行运算分析，快速预判术后是否导致骨折断端断裂。     

基于有限元法的下颈椎弓根螺钉人工椎体系统研究

本实验利用有限元法对下颈椎前路椎弓根螺钉人工椎体系统进行研究,采用有限元法对构建下颈椎的生物力学稳定性及应力情况进行分析,进而对椎弓根螺钉进行优化设计,为临床医用提供进一步的理论。通过对患者的下颈椎处进行CT扫描,获得DICOM数据导入Mimics中,根据不同HU值范围构建下颈椎参数,并运用蒙板编辑、阈值选取、三维增长等工具建立颈椎结构区域的三维模型。采用ANSYS对建立构建的三维下颈椎模型进行有限元分析。构建人体下颈椎有限元模型,对皮质骨、软骨终板等椎间韧带结构进行模拟,设计的下颈椎模型单元有276 382个,节点有413 522个。研究表明,下颈椎在侧弯、屈伸、旋转等六个工况下的ROM椎间值与Panjabi及Kallemeyn等实验研究进行对比,实验数值与Panjabi的实验很近似,且都处于有效区间内,进而证实了实验模型的可行性与有效性。对设计的模型进行网格划分,AVB组设置273 347个单元,378 746个节点,AP组设置265 634个单元,374 593个节点。AP组相较于AVB组的应力峰值明显有增大趋势,但是AVB组的应力情况呈现均匀分布,最大应力主要分布在螺钉尾部及L形钛板与人工椎体接触部位;AP组的最大应力分布在前路钛板的钛网、中上部、螺钉钉杆尾端以及上下椎体接触部位,在钉板连接部位AP组出现应力集中现象。     

应用电子散斑干涉术对单端固定桥的受载分析

本文目的是对单端固定桥的运动及其受力状态进行试验性研究。采用电子散斑干涉术这一新的光学技术分别对下颌单端固定桥修复前后进行４种垂直加载测试,观察实时显示的散斑干涉条纹图,并测量相应牙槽骨处的离面位移。     

锁定钢板、交叉金属螺钉和可吸收螺钉固定治疗跟骨关节内骨折的生物力学比较

锁定钢板与经皮交叉螺钉(金属/可吸收螺钉)均可用于跟骨关节内骨折的临床治疗,但对三者间的生物力学稳定性差异目前尚缺乏了解.本研究拟对此进行分析,通过对一例尸体跟骨标本进行断层扫描,建立完整跟骨与典型SanderⅢ型跟骨骨折的三维有限元模型,对骨折模型分别模拟采用锁定钢板、交叉金属螺钉以及交叉可吸收螺钉固定,经距下关节对跟骨施加垂直向下载荷模拟跟骨的受力状况.有限元模型通过相同来源的跟骨标本进行验证.研究结果显示,完整跟骨的结构刚度高于骨折模型.3种骨折模型中,钢板固定刚度最高,但应力也高于两种螺钉固定模型.钢板固定模型的骨折端位移与金属螺钉固定模型相当,但小于可吸收螺钉固定模型.研究认为,锁定钢板和交叉螺钉均可用于跟骨关节内骨折的治疗,但金属螺钉固定可作为首选方案,因为其具有足够的生物力学稳定性,同时应力遮挡效应较小.     

A comparison of stress distributions for different surgical procedures, screw dimensions and orientations for a Temporomandibular joint implant

Finite element analysis is a useful analytical tool for the design of biomedical implants. The aim of this study was to investigate the behavior of temporomandibular joint implants with multiple design variables of the screws used for fixation of the implant. A commercially available implant with full mandible was analyzed using a finite element software package. The effects of different design variables such as orientation, diameter and stem length of the screws on the stress distribution in bone for two different surgical procedures were investigated. Considering the microstrain in bone as a principal factor, the acceptable ranges for screw diameter and length were determined. Parallel orientation of the screws performed better from a stress point of view when compared to the zig-zag orientation. Sufficient contact between the implant collar and mandibular condyle was shown to reduce the peak stresses which may lead to long term success. The distance between screw holes in the parallel orientation was much closer when compared to the zig-zag orientation. However, the stresses in bone near the screw hole area for the parallel orientation were within acceptable limits.     

A customized fixation plate with novel structure designed by topological optimization for mandibular angle fracture based on finite element analysis

Background

The purpose of this study was to design a customized fixation plate for mandibular angle fracture using topological optimization based on the biomechanical properties of the two conventional fixation systems, and compare the results of stress, strain and displacement distributions calculated by finite element analysis (FEA).

Methods

A three-dimensional (3D) virtual mandible was reconstructed from CT images with a mimic angle fracture and a 1 mm gap between two bone segments, and then a FEA model, including volume mesh with inhomogeneous bone material properties, three loading conditions and constraints (muscles and condyles), was created to design a customized plate using topological optimization method, then the shape of the plate was referenced from the stress concentrated area on an initial part created from thickened bone surface for optimal calculation, and then the plate was formulated as “V” pattern according to dimensions of standard mini-plate finally. To compare the biomechanical behavior of the “V” plate and other conventional mini-plates for angle fracture fixation, two conventional fixation systems were used: type A, one standard mini-plate, and type B, two standard mini-plates, and the stress, strain and displacement distributions within the three fixation systems were compared and discussed.

Results

The stress, strain and displacement distributions to the angle fractured mandible with three different fixation modalities were collected, respectively, and the maximum stress for each model emerged at the mandibular ramus or screw holes. Under the same loading conditions, the maximum stress on the customized fixation system decreased 74.3, 75.6 and 70.6% compared to type A, and 34.9, 34.1, and 39.6% compared to type B. All maximum von Mises stresses of mandible were well below the allowable stress of human bone, as well as maximum principal strain. And the displacement diagram of bony segments indicated the effect of treatment with different fixation systems.

Conclusions

The customized fixation system with topological optimized structure has good biomechanical behavior for mandibular angle fracture because the stress, strain and displacement within the plate could be reduced significantly comparing to conventional “one mini-plate” or “two mini-plates” systems. The design methodology for customized fixation system could be used for other fractures in mandible or other bones to acquire better mechanical behavior of the system and improve stable environment for bone healing. And together with SLM, the customized plate with optimal structure could be designed and fabricated rapidly to satisfy the urgent time requirements for treatment.

     

Influences of geometrical and mechanical properties of bone tissues in mandible behaviour – experimental and numerical predictions

The properties and geometry of bone in the mandible play a key role in mandible behaviour during a person’s lifetime, and attention needs to be paid to the influence of bone properties. We analysed the effect of bone geometry, size and bone properties in mandible behaviour, experimenting on cadaveric mandibles and FE models. The study was developed using the geometry of a cadaveric mandible without teeth. Three models of cadaveric condyles were experimentally tested with instrumented with four rosettes, and a condyle reaction of 300 N. Four finite element models were considered to validate the experiments and analyse mandible behaviour. One numeric model was simulated with 10 muscles in a quasi-static condition. The experimental results present different condyle stiffness’s, of 448, 215 and 254 N/mm. The values presented in the rosettes are influenced by bone geometry and bone thickness; maximum value was ?600 με in rosette #4, and the maximum strain difference between mandibles was 111%. The numerical results show that bone density decreases and strain distribution increases in the thinner mandible regions. Nevertheless, the global behaviour of the structure remains similar, but presents different strain magnitudes. The study shows the need to take into account bone characteristics and their evolutions in order to improve implant design and fixation throughout the patient life. The change in bone stiffness promotes a change in maximum strain distribution with same global behaviour.     

Mechanical analysis of a rodent segmental bone defect model: The effects of internal fixation and implant stiffness on load transfer

Segmental bone defect animal models are often used for evaluating the bone regeneration performance of bone substituting biomaterials. Since bone regeneration is dependent on mechanical loading, it is important to determine mechanical load transfer after stabilization of the defect and to study the effects of biomaterial stiffness on the transmitted load. In this study, we assess the mechanical load transmitted over a 6 mm femur defect that is stabilized with an internal PEEK fixation plate. Subsequently, three types of selective laser melted porous titanium implants with different stiffness values were used to graft the defect (five specimens per group). In one additional group, the defect was left empty. Micro strain gauges were used to measure strain values at four different locations of the fixation plate during external loading on the femoral head. The load sharing between the fixation plate and titanium implant was highly variable with standard deviations of measured strain values between 31 and 93% of the mean values. As a consequence, no significant differences were measured between the forces transmitted through the titanium implants with different elastic moduli. Only some non-significant trends were observed in the mean strain values that, consistent with the results of a previous finite element study, implied the force transmitted through the implant increases with the implant stiffness. The applied internal fixation method does not standardize mechanical loading over the defect to enable detecting small differences in bone regeneration performances of bone substituting biomaterials. In conclusion, the fixation method requires further optimization to reduce the effects of the operative procedure and make the mechanical loading more consistent and improve the overall sensitivity of this rat femur defect model.     

Three-dimensional finite element stress analysis of the dentate human mandible.

The biomechanical events which accompany functional loading of the human mandible are not fully understood. The techniques normally used to record them are highly invasive. Computer modelling offers a promising alternative approach in this regard, with the additional ability to predict regional stresses and strains in inaccessible locations. In this study, we built two three-dimensional finite element (FE) models of a human mandible reconstructed from tomographs of a dry dentate jaw. The first model was used for a complete mechanical characterization of physical events. It also provided comparative data for the second model, which had an increased vertical corpus depth. In both cases, boundary conditions included rigid restraints at the first right molar and endosteal cortical surfaces of the articular eminences of temporal bones. Groups of parallel multiple vectors simulated individual masticatory muscle loads. The models were solved for displacements, stresses, strains, and forces. The simulated muscle loads in the first model deformed the mandible helically upward and toward its right (working) side. The highest principal stresses occurred at the bite point, anterior aspects of the coronoid processes, symphyseal region, and right and left sides of the mandibular corpus. In general, the observed principal stresses and strains were highest on the periosteal cortical surface and alveolar bone. At the symphyseal region, maximum principal stresses and strains were highest on the lower lingual mandibular aspect, whereas minimum principal stresses and strains were highest on its upper labial side. Subcondylar principal strains and condylar forces were higher on the left (balancing or nonbiting) side than on the right mandibular side, with condylar forces more concentrated on the anteromedial aspect of the working-side condyle and on the central and lateral aspects of the left. When compared with in vivo strain data from macaques during comparable biting events, the predictive strain values from the first model were qualitatively similar. In the second model, the reduced tensile stress on the working-side, and decreased shear stress bilaterally, confirmed that lower stresses occurred on the lower mandibular border with increased jaw depth. Our results suggested that although the mandible behaved in a beam-like manner, its corpus acted more like a combination of open and closed cross sections due to the presence of tooth sockets, at least for the task modelled.(ABSTRACT TRUNCATED AT 400 WORDS)     

Evaluation of contributions of orthodontic mini-screw design factors based on FE analysis and the Taguchi method

This study determines the relative effects of changes in bone/mini-screw osseointegration and mini-screw design factors (length, diameter, thread shape, thread depth, material, head diameter and head exposure length) on the biomechanical response of a single mini-screw insertion. Eighteen CAD and finite element (FE) models corresponding to a Taguchi L₁₈ array were constructed to perform numerical simulations to simulate mechanical responses of a mini-screw placed in a cylindrical bone. The Taguchi method was employed to determine the significance of each design factor in controlling strain. Simulation results indicated that mini-screw material, screw exposure length and screw diameter were the major factors affecting bone strain, with percentage contributions of 63%, 24% and 7%, respectively. Bone strain decreased obviously when screw material had the high elastic modulus of stainless/titanium alloys, a small exposure length and a large diameter. Other factors had no significanton bone strain. The FE analysis combined with the Taguchi method efficiently identified the relative contributions of several mini-screw design factors, indicating that using a strong stainless/titanium alloys as screw material is advantageous, and increase in mechanical stability can be achieved by reducing the screw exposure length. Simulation results also revealed that mini-screw and bone surface contact can provide sufficient mechanical retention to perform immediately load in clinical treatment.     

Growth in the area of the inferior dental foramen of rats

The object of the present investigation was to see if the bone around the inferior dental nerve remodelled during mandibular growth and development. The investigation was carried out by injecting 27 albino Lewis rats with three fluorescent bone seeking dyes--oxytetracycline HCl (OTC), alizarin red S (ARS), and 2,4 bis-[N,N'-di' (carbomethyl-aminomethyl)] fluorescein (DCAF)--and then studying the bone around the inferior dental foramen. The mandibles of the animals were studied both macroscopically and microscopically under ultraviolet light to investigate the growth processes occurring and to see if the inferior dental foramen was relocated during growth. A quantitative analysis utilizing two specimens was also carried out for the same purpose. The results of both the qualitative and the quantitative analyses showed that the bone around the inferior dental nerve remodeled during mandibular growth. The mandible grew in an upward and backward direction, and the inferior dental foramen was correspondingly relocated in an upward and backward direction to maintain exactly the same position relative to the condyle and the posterior border of the ramus. This study, then, supports Moss's concept of the "unloaded" nerve, and is in keeping with his view of mandibular growth based on the functional matrix theory.     

Reverse engineering of mandible and prosthetic framework: Effect of titanium implants in conjunction with titanium milled full arch bridge prostheses on the biomechanics of the mandible

This study aimed at investigating the effects of titanium implants and different configurations of full-arch prostheses on the biomechanics of edentulous mandibles. Reverse engineered, composite, anisotropic, edentulous mandibles made of a poly(methylmethacrylate) core and a glass fibre reinforced outer shell were rapid prototyped and instrumented with strain gauges. Brånemark implants RP platforms in conjunction with titanium Procera one-piece or two-piece bridges were used to simulate oral rehabilitations. A lateral load through the gonion regions was used to test the biomechanical effects of the rehabilitations. In addition, strains due to misfit of the one-piece titanium bridge were compared to those produced by one-piece cast gold bridges. Milled titanium bridges had a better fit than cast gold bridges. The stress distribution in mandibular bone rehabilitated with a one-piece bridge was more perturbed than that observed with a two-piece bridge. In particular the former induced a stress concentration and stress shielding in the molar and symphysis regions, while for the latter design these stresses were strongly reduced. In conclusion, prosthetic frameworks changed the biomechanics of the mandible as a result of both their design and manufacturing technology.