Fatigue Loading Effect in Custom-Made All-on-4 Implants System: A 3D Finite Elements Analysis

ObjectivesThis study aims to evaluate the fatigue stress around custom-made all-on-4 implants system to find out which type of implants have a better performance under different graded multidirectional occlusal forces.Material and methods3D normal and implanted models simulating the “All-on-4” concept were created and analyzed under three different conditions of occlusal loadings. Two types of static and fatigue were applied. Stress distribution was analyzed based on von Mises and Goodman theories in ANSYS environment in addition to the safety factor. Statistical tests were performed to assess the significance of the results as well as the reproducibility of the results.ResultsThe results showed stress increasing reaching a value of 48%, 29% in tilted implants compared to vertical implants and normal cases respectively. In contrast, tilted implants appeared to be less stable (safety factor may reach 0.7) and they may fail during the application of occlusal forces. The safety factor of cortical bone decreased by about 91% in the implanted model compared to the normal model, indicating a higher possibility of bone remodeling around the bone.ConclusionThe orientation and position of occlusal forces had an important influence on stress distribution between the implant and the surrounding bone, and fatigue loading caused greater stresses in comparison with static loading. Lower amounts of stress were found in the vertical implants, ensuring a higher safety factor and a longer clinical service. In contrast, the critical safety factor values are observed in tilted implants, which may fail under the influence of applied occlusal forces.     

On the Effects of Cyclic Transversal Forces on Osseointegrated Dental Implants: Experimental and Finite Element Shakedown Analyses

This paper is concerned with the mechanical strength of fixed osseointegrated dental implants subjected to cyclic external loads, applied mainly in a direction orthogonal to their axis. Such a loading condition, seen as a basic design action for the implant, has been given little attention so far. Experimental results and numerical simulations, performed on two- and three-dimensional Finite Element models, are discussed. The shakedown theory is used to show that a common implant design (threaded fixture-abutment-connection screw) is susceptible of low-cycle fatigue failure under loading conditions well within the working range, even if the same design is able to withstand loading of the same type, but applied monotonically, much in excess of the working values. The shakedown analyses give an indication of several possible failure modalities: the low-cycle fatigue either of the implant or of the connection screw, or the loosening of the connection screw itself. Experimental and numerical results are in good qualitative agreement, and both suggest that the issue of transversal cyclic loading on fixed dental implants should be carefully reconsidered in the design phase.     

Biomechanical evaluation of the natural abutment teeth in combined tooth-implant-supported telescopic prostheses: a three-dimensional finite element analysis

Telescopic overdentures supported by the combination of natural teeth and implants have been thought a valuable treatment for the severely compromised partially edentulous patients. But the combination of teeth and implants involves highly complex biomechanical problems. This study is to evaluate biomechanical behaviors of the natural abutment teeth with the treatment of combined tooth-implant supported telescopic crown prostheses in mandible through 3D FEA. According to this study, the prosthetic option supported by a combination of teeth and implants and retained by double crowns could protect teeth and their periodontal support tissues acting as a rigid splint, and may be a valuable treatment option for partially edentulous patients with severely reduced remaining teeth in mandible.     

The Influence of Cavity Shape on the Stresses in Composite Dental Restorations: A Finite Element Study

Dental restoration adhering to the cavity exhibits fundamentally different load transfer mechanisms from non-adhering restorations. It is therefore questionable that traditional cavity designs are optimal from a purely mechanical point of view when working with composite materials. Drawing from general engineering experience, it can be hypothesised that smooth, well rounded designs with bevelled margins are superior. A finite element model is used in the present investigation to determine the stress field in four different cavity designs as it develops during the curing of the restoration. The results show that a significant reduction of the stress along the adhesive interface between the tooth and the restoration can be achieved through the use of a rounded cavity shape. They also show that the adoption of bevelled margins leads to a reduction of the stress concentration at this location. These results are confirmed by a set of experimental results published in the literature. It is concluded that adhering restorations will perform better from a mechanical point of view if an appropriate cavity shape is selected.     

Influence of transmucosal height in abutments of single and multiple implant-supported prostheses: a non-linear three-dimensional finite element analysis

The aim of this study was to analyze the influence of three different transmucosal heights of the abutments in single and multiple implant-supported prostheses through the finite element method. External hexagon implants, MicroUnit, and EsthetiCone abutments were scanned and placed in an edentulous maxillary model obtained from a tomography database. The simulations were divided into two groups: (1) one implant with 3.75 × 10 mm placed in the upper central incisor, simulating a single implant-supported fixed prosthesis with an EsthetiCone abutment; and (2) two implants with 3.75 × 10 mm placed in the upper lateral incisors with MicroUnit abutments, simulating a multiple implant-supported prosthesis. Subsequently, each group was subdivided into three models according to the transmucosal height (1, 2, and 3 mm). A static oblique load at an angle of 45 degrees to the long axis of the implant in palatal-buccal direction of 150 and 75 N was applied for multiple and single implant-supported prosthesis, respectively. The implants and abutments were assessed according to the equivalent Von Mises stress analyses while the bone and ceramics were analyzed through maximum and minimum principal stresses. The total deformation values increased in all models, while the transmucosal height was augmented. The transmucosal height of the abutments influences the stress values at the bone, ceramics, implants, and abutments of both the single and multiple implant-supported prostheses, with the transmucosal height of 1 mm showing the lowest stress values.     

Bone ingrowth on the surface of endosseous implants. Part 2: Theoretical and numerical analysis

The study of osseointegration of endosseous implants is a matter of great interest, mostly due to the increase in the use of many types of implants in clinical practice. Bone ingrowth results from a complex process, in which mechanics and biology play a major role. A wide variety of diverse factors can affect the development of the process, such as the properties or geometry of the implant surface, the mechanical stimulation or the initial cell conditions. In the first part of this article [Moreo, P., García-Aznar, J.M., Doblaré, M., 2008. Bone ingrowth on the surface of endosseous implants. Part 1: mathematical model. J. Theor. Biol., in press] a model composed of a set of reaction–diffusion equations was proposed to simulate the formation of bone around implants, specially focused on the early stages of bone healing, that was able to contemplate the effects of surface microtopography. The goal of this second part is to use the model to analyse the effect of factors such as cell stimulation, the initial cell concentration in the host bone and the geometry of the implant. For this purpose, two different simplified versions of the model are here analysed theoretically and further insight is gained from the study of the stability of fixed points and existence of travelling waves. Additionally, numerical simulations by means of the finite element method have been performed to examine the osseointegration of a dental implant with grooves at the surface of the threads. Results obtained from the analysis and simulations show that the model can reproduce some features of peri-implant bone ingrowth.     

3D finite element model of the diabetic neuropathic foot: A gait analysis driven approach

Diabetic foot is an invalidating complication of diabetes that can lead to foot ulcers. Three-dimensional (3D) finite element analysis (FEA) allows characterizing the loads developed in the different anatomical structures of the foot in dynamic conditions. The aim of this study was to develop a subject specific 3D foot FE model (FEM) of a diabetic neuropathic (DNS) and a healthy (HS) subject, whose subject specificity can be found in term of foot geometry and boundary conditions. Kinematics, kinetics and plantar pressure (PP) data were extracted from the gait analysis trials of the two subjects with this purpose. The FEM were developed segmenting bones, cartilage and skin from MRI and drawing a horizontal plate as ground support. Materials properties were adopted from previous literature. FE simulations were run with the kinematics and kinetics data of four different phases of the stance phase of gait (heel strike, loading response, midstance and push off). FEMs were then driven by group gait data of 10 neuropathic and 10 healthy subjects. Model validation focused on agreement between FEM-simulated and experimental PP.     

Influence of plaque calcifications on coronary stent fracture: A numerical fatigue life analysis including cardiac wall movement

Coronary stent fracture is still an unresolved issue in the field of minimally invasive cardiovascular interventions due to its high rate of incidence and uncertain clinical consequences. Recent studies, based on clinical data, proved that there are several factors which can be identified as independently responsible of coronary stent fracture. Among these, calcifications, which increase the local stiffness and heterogeneity of atherosclerotic plaques, seem to play a major role. From a mechanical point of view, stent fracture in coronary arteries is triggered by the cyclic loading of pulsatile blood pressure combined with the movement of cardiac wall.     

3 种不同弹性模量钛合金股骨假体在羊股骨置换模型中应力分布的三维 有限元分析

目的:通过三维有限元分析方法来观察并比较3种不同弹性模量钛合金股骨假体在羊股骨置换模型中von-Mises应力分布的情况。方法:采用64排螺旋CT对一健康成年羊的下肢股骨进行全长的CT扫描,扫描层厚为0.5 mm,扫描所得的数据存储为DICOM文件。将得到的DICOM文件导入到CT图像分析软件Mimics 10.0,然后利用Mimics 10.0软件来生成股骨的骨质点云数据,再将生成的骨质点云数据导入到Simpleware分析软件,通过机械加工反求中的复杂曲面造型技术建立起精确的三维实体模型。对三维实体模型进行网格划分,确定了髓腔的形状,并根据羊下肢股骨髓腔的形状设计了作者实验用的羊股骨假体模型,然后在ANSYS 12.1软件中进行网格划分。给予加载缓慢行走载荷以及扭转载荷,分析并比较羊股骨以及3种不同弹性模量钛合金股骨假体在股骨置换模型中von-Mises应力分布的情况。结果:在缓慢行走载荷以及扭转载荷条件下,3种不同弹性模量钛合金股骨假体von-Mises应力分布变化趋势一致,假体的柄颈结合部以及假体柄上1/3为应力集中区域。3种不同弹性模量的最大应力集中点均位于柄颈结合部,60 GPa弹性模量的股骨假体植入后假体的最大应力最小(37.8 MPa、29.1 MPa),股骨的最大应力最大(12.6 MPa、24.5 MPa);80 GPa的次之,假体的最大应力(38.4 MPa、33.4 MPa),股骨的最大应力(12.5 MPa、24.5 MPa);110 GPa的股骨假体植入后假体的最大应力最大(38.9 MPa、38.1 MPa),股骨的最大应力最小(12.3 MPa、24.5 MPa)。60 GPa弹性模量的股骨假体植入后的假体最大位移和相对位移均最小(缓慢行走载荷下假体最大位移为0.551 mm、相对位移为0.008 mm,扭转载荷下假体最大位移为0.730 mm、相对位移为0.011 mm)。结论:较低弹性模量的钛合金股骨假体(60 GPa)由于其弹性模量更接近于骨组织的弹性模量,股骨假体与股骨间的"应力遮挡"效应较小,更有利于应力在股骨假体及股骨间的传递,增加了股骨假体的早期稳定性,延长了其临床寿命。     

分析塞来昔布与不同剂量艾瑞昔布治疗axSpA的效果及对骨代谢的影响

目的:探究塞来昔布和2种剂量艾瑞昔布治疗中轴脊柱关节炎(axSpA)的效果及对患者骨代谢的影响。方法:选取我院96例axSpA患者为研究对象,采用随机数字表法分为A组、B组、C组各32例。A组给予0.2 g/d艾瑞昔布治疗,B组给予0.4 g/d艾瑞昔布治疗C组给予0.4 g/d塞来昔布治疗。比较3组治疗前及治疗12周后疾病活动性[C反应蛋白(CRP)、红细胞沉降率(ESR)、Bath强直性脊柱炎疾病活动指数(BASDAI)]、躯体活动度(踝间距、腰椎侧弯度)、功能状态[Bath强直性脊柱炎功能指数(BASFI)、加拿大脊柱骨关节研究协会评分系统(SPARCC)]、骨代谢[血清骨形成发生蛋白-2(BMP-2)、血管内皮生长因子(VEGF)、Dickkopf相关蛋白1(DKK-1)]差异,并记录3组治疗期间不良反应发生情况。结果:治疗12周后,3组疾病活动性(CRP、ESR、BASDAI)、功能状态(BASFI、SPARCC)、骨代谢(BMP-2、VEGF、DKK-1)均较治疗前降低(P<0.05),躯体活动度(踝间距及左右侧腰椎侧弯度)则较治疗前升高(P<0.05);但B组及C组组间比较,差异无统计学意义(P>0.05),而A组上述指标变化幅度低于B组及C组(P<0.05)。3组治疗期间不良反应发生情况比较,差异均无统计学意义(P>0.05)。结论:较高剂量(0.4 g/d)艾瑞昔布疗效明显优于较低剂量(0.2 g/d),不良反应也未增加,且0.4 g/d艾瑞昔布及同剂量塞来昔布治疗axSpA具有相似的疗效及安全性,适用于临床治疗。     

The nutrition of the human meniscus: A computational analysis investigating the effect of vascular recession on tissue homeostasis

The meniscus is essential to the functioning of the knee, offering load support, congruency, lubrication, and protection to the underlying cartilage. Meniscus degeneration affects ∼35% of the population, and potentially leads to knee osteoarthritis. The etiology of meniscal degeneration remains to be elucidated, although many factors have been considered. However, the role of nutritional supply to meniscus cells in the pathogenesis of meniscus degeneration has been so far overlooked. Nutrients are delivered to meniscal cells through the surrounding synovial fluid and the blood vessels present in the outer region of the meniscus. During maturation, vascularization progressively recedes up to the outer 10% of the tissue, leaving the majority avascular. It has been hypothesized that vascular recession might significantly reduce the nutrient supply to cells, thus contributing to meniscus degeneration. The objective of this study was to evaluate the effect of vascular recession on nutrient levels available to meniscus cells. This was done by developing a novel computational model for meniscus homeostasis based on mixture theory. It was found that transvascular transport of nutrients in the vascularized region of the meniscus contributes to more than 40% of the glucose content in the core of the tissue. However, vascular recession does not significantly alter nutrient levels in the meniscus, reducing at most 5% of the nutrient content in the central portion of the tissue. Therefore, our analysis suggests that reduced vascularity is not likely a primary initiating source in tissue degeneration. However, it does feasibly play a key role in inability for self-repair, as seen clinically.     

Cervical spine morphology and ligament property variations: A finite element study of their influence on sagittal bending characteristics

Cervical spine finite element models reported in biomechanical literature usually represent a static morphology. Not considering morphology as a model parameter limits the predictive capabilities for applications in personalized medicine, a growing trend in modern clinical practice. The objective of the study was to investigate the influence of variations in spinal morphology on the flexion-extension responses, utilizing mesh-morphing-based parametrization and metamodel-based sensitivity analysis. A C5-C6 segment was used as the baseline model. Variations of intervertebral disc height, facet joint slope, facet joint articular processes height, vertebral body anterior-posterior depth, and segment size were parametrized. In addition, material property variations of ligaments were considered for sensitivity analysis. The influence of these variations on vertebral rotation and forces in the ligaments were analyzed. The disc height, segmental size, and body depth were found to be the most influential (in the cited order) morphology variations; while among the ligament material property variations, capsular ligament and ligamentum flavum influenced vertebral rotation the most. Changes in disc height influenced forces in the posterior ligaments, indicating that changes in the anterior load-bearing column of the spine could have consequences on the posterior column. A method to identify influential morphology variations is presented in this work, which will help automation efforts in modeling to focus on variations that matter. This study underscores the importance of incorporating influential morphology parameters, easily obtained through computed tomography/magnetic resonance images, to better predict subject-specific biomechanical responses for applications in personalized medicine.     

Nd:YAG激光联合Icon渗透树脂治疗氟斑牙患者效果及对美学效果的影响

摘要 目的：探讨Nd:YAG激光联合Icon渗透树脂治疗氟斑牙患者效果及对美学效果的影响。方法：选择2018年6月至2023年6月来我院诊治的氟斑牙患者80例,共有486颗患牙,根据随机数字表法将80例患者分为两组,对照组行Nd:YAG激光治疗,观察组行Nd:YAG激光联合Icon渗透树脂治疗。对比两组不同时间点的色阶变化情况、漂白疗效、病损面积比、患牙牙釉质硬度,对比治疗过程中两组患者的牙齿敏感度及患者满意度。结果：治疗后即刻、治疗后12周,两组的色阶降低,且同时间点观察组与对照组相比较低（P<0.05）。治疗后即刻,观察组有效率84.17%明显较对照组76.42%高（P<0.05）,治疗后12周,观察组有效94.17%明显较对照组82.93%高（P<0.05）。治疗后即刻、12周两组的病损面积比降低,且同时间点观察组与对照组相比较低（P<0.05）。与治疗前及观察组相比,对照组治疗后即刻、12周时的患牙牙釉质硬度较低（P<0.05）。观察组的牙齿敏感度、满意度明显优于对照组（P<0.05）。结论：Nd:YAG激光联合Icon渗透树脂可提高氟斑牙患牙的疗效,缩小病损面积比、患牙敏感度,提高美学效果,且不影响患牙牙釉质硬度,其是氟斑牙具有潜能的治疗方法。     

南京市玄武区3～5岁儿童龋病的影响因素分析及对生长发育和营养素摄入的影响

摘要 目的：对南京市玄武区3～5岁儿童患龋病进行流行病学调查,并分析患龋病的影响因素,及其对生长发育和营养素摄入的影响。方法：2020年3月~2022年2月期间,采用多阶段分层等容量随机抽样方法,随机抽取南京市玄武区6所幼儿园,共抽取792名3～5岁儿童,实际完成调查788人,响应率99.49%。记录南京市玄武区3～5岁儿童龋病发生情况,根据有无龋病发生分为龋病组（n=361）和无龋病组（n=427）。应用单因素和多因素Logistic回归性分析南京市玄武区3～5岁儿童龋病发生的影响因素。并观察龋病发生对儿童生长发育和营养素摄入的影响。结果：788例3～5岁儿童中,检查出存在龋病361人,发病率为45.81%。单因素分析显示,南京市玄武区3～5岁儿童龋病发生与年龄、喂养方式、糖摄入频次、睡前食用甜点、刷牙次数、开始刷牙年龄、家长口腔健康知识水平有关（P<0.05）。多因素Logistic回归性分析结果显示：年龄为5岁、喂养方式为全母乳、糖摄入频次为≥2次/d、睡前食用甜点是南京市玄武区3～5岁儿童龋病发生的危险因素（P<0.05）,而家长口腔健康知识水平较高是南京市玄武区3～5岁儿童龋病发生的保护因素（P<0.05）。无龋病组的身高、体重、胸围、肺活量均大于龋病组（P<0.05）。龋病组的能量、蛋白质、脂肪、钙、铁、锌、维生素C、叶酸低于无龋病组（P<0.05）。结论：南京市玄武区3～5岁儿童龋病的发病率较高,龋病对生长发育和营养素摄入均有一定的影响,而年龄、喂养方式、糖摄入频次、睡前食用甜点、家长口腔健康知识水平均是龋病发生的影响因素。     

The Effects of Prolonged Cryopreservation on the Biomechanical Properties of Bone Allografts: A Microbiological, Histological and Mechanical Study

Bone allografting is the most common form of allotransplantation in modern medicine. Bone banking is usually the major part of most tissue banks throughout the world. Several years ago, many standards of bone banking were set empirically, and have never been evaluated. One particular parameter or standard was outdating graft materials after 5 years of storage. This study was conducted to evaluate the effect of prolonged cryopreservation on the biomechanical properties of bone allografts and establish whether graft materials become contaminated during long-term storage.Proximal humeral bone allografts were obtained from the bone bank after 1, 3 and 5 years of –80°C cryopreservation. Samples of each humeral head, i.e., cartilage, subchondral bone and spongy bone were histologically examined for inter- and intra-cellular changes. A three-point mechanical bending test was used on identical pieces of cortical bone to compare fresh and cryopreserved materials. Fresh-retrieved cortical bone using identically-sized segments, served as a control. Cultures were taken from each respective sample to determine contamination or sterility.Results of both the histological and mechanical testing showed that there were no significant, qualitative histological, or quantitative mechanical differences among the samples. All the cultures were negative. Therefore, based on this study's parameters, bone allografts can safely be used after a cryopreservation period of over 5 years and should not be discarded.     

Effects of lumbo-pelvic rhythm on trunk muscle forces and disc loads during forward flexion: A combined musculoskeletal and finite element simulation study

Previous in-vivo studies suggest that the ratio of total lumbar rotation over pelvic rotation (lumbo-pelvic rhythm) during trunk sagittal movement is essential to evaluate spinal loads and discriminate between low back pain and asymptomatic population. Similarly, there is also evidence that the lumbo-pelvic rhythm is key for evaluation of realistic muscle and joint reaction forces and moments predicted by various computational musculoskeletal models. This study investigated the effects of three lumbo-pelvic rhythms defined based on in-vivo measurements on the spinal response during moderate forward flexion (60°) using a combined approach of musculoskeletal modeling of the upper body and finite element model of the lumbosacral spine. The muscle forces and joint loads predicted by the musculoskeletal model, together with the gravitational forces, were applied to the finite element model to compute the disc force and moment, intradiscal pressure, annular fibers strain, and load-sharing. The results revealed that a rhythm with high pelvic rotation and low lumbar flexion involves more global muscles and increases the role of the disc in resisting spinal loads, while its counterpart, with low pelvic rotation, recruits more local muscles and engages the ligaments to lower the disc loads. On the other hand, a normal rhythm that has balanced pelvic and lumbar rotations yields almost equal disc and ligament load-sharing and results in more balanced synergy between global and local muscles. The lumbo-pelvic rhythm has less effect on the intradiscal pressure and annular fibers strain. This work demonstrated that the spinal response during forward flexion is highly dependent on the lumbo-pelvic rhythm. It is therefore, essential to adapt this parameter instead of using the default values in musculoskeletal models for accurate prediction of muscle forces and joint reaction forces and moments. The findings provided by this work are expected to improve knowledge of spinal response during forward flexion, and are clinically relevant towards low back pain treatment and disc injury prevention.     

A unique feeding strategy of the extinct marine mammal Kolponomos: convergence on sabretooths and sea otters

Mammalian molluscivores feed mainly by shell-crushing or suction-feeding. The extinct marine arctoid, Kolponomos, has been interpreted as an otter-like shell-crusher based on similar dentitions. However, neither the masticatory biomechanics of the shell-crushing adaptation nor the way Kolponomos may have captured hard-shelled prey have been tested. Based on mandibular symphyseal morphology shared by Kolponomos and sabre-toothed carnivores, we hypothesize a sabretooth-like mechanism for Kolponomos prey-capture, whereby the mandible functioned as an anchor. Torque generated from jaw closure and head flexion was used to dislodge prey by prying, with prey then crushed using cheek teeth. We test this hypothesized feeding sequence using phylogenetically informed biomechanical simulations and shape analyses, and find a strongly supported, shared high mandibular stiffness in simulated prey-capture bites and mandibular shape in Kolponomos and the sabre-toothed cat Smilodon. These two distantly related taxa converged on using mandibles to anchor cranial torqueing forces when prying substrate-bound prey in the former and sabre-driving forces during prey-killing in the latter. Simulated prey-crushing bites indicate that Kolponomos and sea otters exhibit alternative structural stiffness-bite efficiency combinations in mandibular biomechanical adaptation for shell-crushing. This unique feeding system of Kolponomos exemplifies a mosaic of form-function convergence relative to other Carnivora.     

A review of methods to trace material flows into final products in dynamic material flow analysis: Comparative application of six methods to the United States and EXIOBASE3 regions,Part 2

Modeling pathways toward sustainable production and consumption requires improved spatio-temporal and material coverage of end-use product stocks. Momentarily, studies on inflow-driven, dynamic material flow analysis (dMFA) extrapolate scarce information on material end-use shares (i.e., ratios that split economy-wide material consumption to different end-use products) for single countries and years across longer time periods and global regions. Therefore, in part 1 of this work, we reviewed five methods to derive material end-use shares which use industry shipment data in physical units and monetary input–output tables (MIOTs). Herein, we comparatively apply these methods to the United States, drawing on detailed national data, as well as the multi-regional input–output model EXIOBASE3. To better match MIOT and dMFA system definitions, we propose the end-use transfer method, which re-routes specific intermediate outputs to final demand in MIOTs. In closing, we conclude on 12 points for improved end-use shares. We find mixed results regarding the fit between end-use shares derived from industry shipments and MIOTs: for detailed national data, we find good fit for some materials (e.g., aluminum), while others deviate strongly (e.g., steel). In many cases, the temporal trend of MIOT-derived end-use shares roughly agrees with industry shipments. For EXIOBASE3, we find good fit for some countries and materials, but substantial mismatches for others. Despite mixed results, combining MIOT-based end-use shares with industry shipments and auxiliary country-level data could enable improved temporal, geographical, and end-use resolution. However, the scarcity, documentation, and quality of input data are key limitations for more accurate and detailed end-use shares. This article met the requirements for a gold-gold data openness badge described at http://jie.click/badges .