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Results for “Finite Element Analysis”

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At least 451 records · Page 25Linked to original sources

PubMed1997

[A three-dimensional anisotropic finite element analysis of modified bar-clip implant-borne overdenture in the edentulous mandible under punching loads].

The stress distributions of the modified bar-clip implant-borne overdenture in the edentulous mandible were performed under punching loads with both porcelain and resin chosen as the restorative materials by means of three-dimensional anisotropic finite element method. The purpose of this study was to investigate the patterns of stress distributions and to compare the effect of different restorative materials on the stress distributions under punching loads. The results showed that the value of stress peaks in implants with porcelain restorations seemed higher than those with resin restorations. On the contrary, in the bone-implant interface had little difference, except a comparative uniform stress distribution found in resin restorations. It implies that resin restoration produces a cushioning effect on reducing the stress peaks in implants themselves under punching loads. Both porcelain and resin restorations can be chosen as the restorative materials because of a little influence on the stress peaks in bone-implant interface under punching loads.

Adult↗

PubMed2006

Finite element analysis of the lumbar spine with a new cage using a topology optimization method.

In recent years, degenerative spinal instability has been effectively treated with a cage. However, little attention is focused on the design concept of the cage. The purpose of this study was to develop a new cage and evaluate its biomechanical function using a finite element method (FEM). This study employed topology optimization to design a new cage and analyze stress distribution of the lumbar spine from L1 to L3 with a new cage by using the commercial software ANSYS 6.0. A total of three finite element models, namely the intact lumbar spine, the spine with double RF cages, and with double new cages, were established. The loading conditions were that 10Nm flexion, extension, lateral bending, and torsion, respectively, were imposed on the superior surface of the L1 vertebral body. The bottom of the L3 vertebral body was constrained completely. The FEM estimated that the new cage not only could be reduced to 36% of the volume of the present RF cage but was also similar in biomechanical performance such as range of motion, stress of adjacent disc, and lower subsidence to the RF cage. The advantage of the new cage was that the increased space allowed more bone graft to be placed and the cage saved material. The disadvantage was that stress of the new cage was greater than that of the RF cage.

Biomechanical Phenomena↗

PubMed2004

Finite element analysis of three designs of an implant-supported molar crown.

STATEMENT OF PROBLEM: The optimal method of implant support for a single mandibular molar crown is controversial because commonly used, threaded, root-form implants developed by Branemark were not originally designed to support individual crowns. PURPOSE: The purpose of this study was to develop a finite element model of a single mandibular first molar crown supported by (1) a standard 3.75-mm-diameter implant, (2) a 5-mm, wide-diameter implant, and (3) double standard-diameter implants, and to compare the induced displacements as a result of various loading conditions. MATERIAL AND METHODS: Three-dimensional finite element models were made to simulate the 3 single-molar implant designs. Each model was analyzed with 2 force magnitudes (35 N and 70 N) and with 2 force directions (vertical and 15 degrees to the vertical axis). Displacements in 3-dimensional space as a result of the simulated loading conditions were evaluated along 3 primary axes, mesiodistal, faciolingual, and superior-inferior. RESULTS: Mesiodistal and buccolingual displacements for the crown supported by the 5-mm-diameter implant were reduced by approximately 50% compared with the crown supported by the 3.75-mm implant when the crowns were loaded at the distobuccal cusp tip or the distal marginal ridge. The double-implant design recorded the least mesiodistal displacement with off-center loading of the crown. CONCLUSION: When the crown was loaded off-center, the double-implant design produced substantially less displacement when compared with either of the single-implant designs.

Biomechanical Phenomena↗

PubMed2001

Finite-element analysis of aortic valve-sparing: influence of graft shape and stiffness.

Aortic valve incompetence due to aortic root dilation may be surgically corrected by resuspension of the native valve within a vascular graft. This study was designed to examine the effect of graft shape and material properties on aortic valve function, using a three-dimensional finite-element model of the human aortic valve and root. First, the normal root elements in the model were replaced with graft elements, in either a cylindrical or a "pseudosinus" shape. Next, the elements were assigned the material properties of either polyethylene terephthalate, expanded polytetrafluoroethylene, or polyurethane. Diastolic pressures were applied, and stresses, strains, and coaptation were recorded for the valve, root, and graft. Regarding shape, the cylindrical graft models increased the valve stresses by up to 173%, whereas the root-shaped graft model increased valve stresses by up to 40% as compared to normal. Regarding material properties, the polyurethane models demonstrated valve stress, strain, and coaptation values closest to normal, for either root shape. Graft shape had a greater effect on the simulated valve function than did the material property of the graft. Optimizing the shape and material design of the graft may result in improved longevity of the spared valve if a normal environment is restored.

Aorta↗

PubMed2002

Finite element analysis of stress around a sternum screw used to prevent sternal dehiscence after heart surgery.

The sternum screw has been proposed as a means of preventing sternal dehiscence, following heart surgery, by increasing the contact area between the wire used to close the median sternotomy and the surrounding bone; as a result, the contact stress is reduced. A finite element model was constructed of a cylindrical wire or screw passing through a block of sternum which consisted of cancellous bone sandwiched within a cortical shell. The thickness of the cortical shell and the material properties of bone were varied between reasonable values. The stress distribution in the sternum was calculated for each model when the wire was subjected to a tension (250 N) which would be required for six wires to withstand a strong cough (40 kPa). Results were validated by comparison with a simple analytical model in which the bone and wire were considered incompressible. They show that the screw reduces the contact stress to almost one-seventh of its value when wire is used alone. Contact stresses are especially high if the cortical shell is thin. The high stress in the bone around a screw falls off within a few millimetres. As a result, no problems are anticipated in placing six screws in each half-sternum so that the sternotomy may be closed with the usual six wires.

Bone Screws↗

PubMed2003

Subject-specific finite element analysis of the human medial collateral ligament during valgus knee loading.

The objectives of this study were (1) to develop subject-specific experimental and finite element (FE) techniques to study the three-dimensional stress-strain behavior of ligaments, with application to the human medial collateral ligament (MCL), and (2) to determine the importance of subject-specific material properties and initial (in situ) strain distribution for prediction of the strain distribution in the MCL under valgus loading. Eight male knees were subjected to varus-valgus loading at flexion angles of 0 degrees, 30 degrees, and 60 degrees. Three-dimensional joint kinematics and MCL strains were recorded during kinematic testing. Following testing, the MCL of each knee was removed to allow measurement of the in situ strain distribution and to perform material testing. A FE model of the femur-MCL-tibia complex was constructed for each knee to simulate valgus loading at each flexion angle, using subject-specific bone and ligament geometry, material properties, and joint kinematics. A transversely isotropic hyperelastic material model was used to represent the MCL. The MCL in situ strain distribution at full extension was used to apply in situ strain to each MCL FE model. FE predicted MCL strains during valgus loading were compared to experimental measurements using regression analysis. The subject-specific FE predictions of strain correlated reasonably well with experimentally measured MCL strains (R(2)=0.83, 0.72, and 0.66 at 0 degrees, 30 degrees, and 60 degrees, respectively). Despite large inter-subject variation in MCL material properties, MCL strain distributions predicted by individual FE models that used average MCL material properties were strongly correlated with subject-specific FE strain predictions (R(2)=0.99 at all flexion angles). However, predictions by FE models that used average in situ strain distributions yielded relatively poor correlations with subject-specific FE predictions (R(2)=0.44, 0.35, and 0.33 at flexion angles of 0 degrees, 30 degrees, and 60 degrees, respectively). The strain distribution within the MCL was nonuniform and changed with flexion angle. The highest MCL strains occurred at full extension in the posterior region of the MCL proximal to the joint line during valgus loading, suggesting this region may be most vulnerable to injury under these loading conditions. This work demonstrates that subject-specific FE models can predict the complex, nonuniform strain fields that occur in ligaments due to external loading of the joint.

Adult↗

PubMed2006

Nonlinear finite element analysis for musculoskeletal biomechanics of medial and lateral plantar longitudinal arch of Virtual Chinese Human after plantar ligamentous structure failures.

BACKGROUND: Musculoskeletal diseases of the foot such as stress fractures, tendonitis and subsequent pain are commonly associated with elevated stresses/strains of abnormal plantar arch after plantar ligamentous structure failures. The goal of this study was to develop anatomically detailed, finite element models of the medial and lateral plantar longitudinal arch, and to investigate bone and muscle stresses resulting from plantar fasciotomy and major plantar ligament injuries. METHODS: Nonlinear finite element models of the second ray and the fifth ray of plantar longitudinal arches were constructed on the basis of CT and MR images of Virtual Chinese Human "female No. 1". The models assumed a balanced standing load configuration. Three different degrees of passive intrinsic muscle tensions (weak, moderate, or severe) were used in conjunction with simulations of plantar fasciotomy and major plantar ligament injury. FINDINGS: Plantar fasciotomy caused von Mises stress increases in the bones and plantar ligaments while major plantar ligament injuries caused stress increases in the bones, flexor tendons, and plantar fascia. Increasing intrinsic muscle passive tensions decreased stress/strain levels in the medial and lateral arch, and adjusted abnormal tension/compression stress flows of both arches to close to the normal biomechanical states. INTERPRETATION: This study shows that plantar longitudinal arches are concordant combination of bony structures, intrinsic muscles, plantar fascia and ligaments. After plantar ligamentous structure failures, intrinsic muscles have to contribute to stabilize the plantar arches. This mechanism may reduce the risk of developing stress fractures, tendonitis and pain syndrome.

Biomechanical Phenomena↗

PubMed2002

A finite element analysis methodology for representing the articular cartilage functional structure.

Recognising that the unique biomechanical properties of articular cartilage are a consequence of its structure, this paper describes a finite element methodology which explicitly represents this structure using a modified overlay element model. The validity of this novel concept was then tested by using it to predict the axial curling forces generated by cartilage matrices subjected to saline solutions of known molality and concentration in a novel experimental protocol. Our results show that the finite element modelling methodology accurately represents the intrinsic biomechanical state of the cartilage matrix and can be used to predict its transient load-carriage behaviour. We conclude that this ability to represent the intrinsic swollen condition of a given cartilage matrix offers a viable avenue for numerical analysis of degenerate articular cartilage and also those matrices affected by disease.

Animals↗

PubMedDate not supplied

Biomechanical rationale for intentionally inclined implants in the posterior mandible using 3D finite element analysis.

PURPOSE: Since natural dental arches usually form Monson or Spee occlusal curvatures among the posterior teeth, they tend to incline in mesial and lingual directions. The purpose of this study was to examine the biomechanical rationale for placing implants according to these curvatures in the mandibular posterior region. MATERIALS AND METHODS: A 3-dimensional finite element model was created in which 2 implants were placed in the mandibular molar area. Stress distribution in the bone around the implants was analyzed under different distal implant inclinations. RESULTS: Stress in the cervical area of the mesial and distal implants and the surrounding bone was higher when the implants were placed parallel to each other compared to when the distal implant was placed with a mesial or mesiolingual inclination. DISCUSSION: The slightly smaller effect of a mesiolingual inclination compared to a mesial inclination can be explained by the large cantilever on the buccal side of the superstructure. CONCLUSION: Within the limitations of this study, it was suggested that there is a biomechanical rationale for placing implants in the posterior mandible area with a mesial inclination similar to that of natural teeth. It was also suggested that too much lingual inclination can put the implant at risk of overload.

Alveolar Process↗

PubMedDate not supplied

Finite element analysis studies of an all-ceramic crown on a first premolar.

PURPOSE: This study examined the effects of using four different core-ceramic materials on the stresses that developed in a single all-ceramic first premolar crown. MATERIALS AND METHODS: This was done by analyzing models constructed in an axisymmetric fashion with finite element analyses. The model had a 600-N vertical load applied uniformly over a circular area on top of the crown. Particular emphasis was placed on the tensile stresses that developed. RESULTS: For this particular type of model and loading configuration, radial tensile stresses were predominant in magnitude. Peak hoop and axial tensile stresses were approximately 80% and 2% of this value, respectively. The peak radial and hoop tensile stresses were located on the inside of the coping and scaled with the elastic modulus of the coping. For the axial component, the peak was located in the veneer ceramic on its outermost perimeter. CONCLUSION: Under normal loading, a near-uniform tensile stress field developed within the coping, directly beneath the contact area. The magnitude of this stress for realistic bite forces using current design recommendations was significantly lower than the fracture strength of the four ceramic materials investigated. The stresses developed within the porcelain were in all instances well below typical strength values.

Aluminum Oxide↗

PubMedDate not supplied

Edge-element based finite element analysis of microwave hyperthermia treatments for superficial tumours on the chest wall.

Several three-dimensional hyperthermia treatment planning systems for deep regional hyperthermia have been successfully utilized for improving the performance of applicators such as the BSD Sigma 60. Treatment planning systems for superficial heating in contrast have been less utilized. This paper presents a study of the applicability of the finite element method that has been developed for modelling hyperthermia treatments of recurrent chest wall cancer using a patient geometry. The patient model was created by reconstructing the tissue geometry of a patient using a series of axial CT scans. Tetrahedral grids were generated from this geometry for use in finite element simulations of the SAR profile using edge-elements and in finite element simulations of the steady-state temperature profile using scalar elements. The predicted temperature profile was well correlated with thermometry readings taken after 30 min of heating during a hyperthermia treatment. The model predicted the presence of hot-spots in regions that were not monitored. Simulations also showed that the hot-spots can be manipulated by rotating the applicator by 90 degrees. This study demonstrates the ability of the model to provide detailed and accurate heating profiles in a patient specific model for superficial microwave hyperthermia of the chest wall.

Computer Simulation↗

PubMed1999

Finite element analysis of the lift on a slightly deformable and freely rotating and translating cylinder in two-dimensional channel flow.

Motivated by the lateral migration phenomena of fresh and glutaraldehyde-fixed red blood cells in a field flow fractionation (FFF) separation system, we studied the transverse hydrodynamic lift on a slightly flexible cylinder in a two-dimensional channel flow. The finite element method was used to analyze the flow field with the cylinder at different transverse locations in the channel. The shape of the cylinder was determined by the pressure on the surface of the cylinder from the flow field solution and by the internal elastic stress. The cylinder deformation and the flow field were solved simultaneously. The transverse lift exerted on the cylinder was then calculated. The axial and angular speed of the cylinder were iterated such that the drag and torque on the cylinder were nulled to represent a freely translating and rotating state. The results showed that the transverse lift on a deformable cylinder increased greatly and the equilibrium position moved closer to the center of the channel compared to a rigid cylinder. Also, with the same elastic modulus but a higher flow rate, a larger deformation and higher equilibrium location were found. The maximum deformation of the cylinder occurred when the cylinder was closest to the wall where a larger shear rate existed. The numerical results and experimental studies are discussed.

Blood Flow Velocity↗

PubMed2005

Effects of cantilever design and material on stress distribution in fixed partial dentures--a finite element analysis.

The purpose of this study was to examine the stress distribution in distal cantilevered fixed partial dentures (FPDs) that are designed with different cantilever morphology and made from different restorative materials. The finite element (FE) method was used to create models of two restoration types; metal-ceramic and an all-ceramic FPDs. Both models were designed with distal cantilevers involving the first and second premolars as abutments and cantilever extension involving at the premolar or molar. The width of connector between the cantilever and the primary abutment restoration was 2.25 mm. The load applied during the FE analysis was positioned at the cusp tips of all teeth. The FE analysis of the models revealed that Von Mises stress values with maximum stress concentrations were observed on connectors of distal cantilevers. Stress concentration sites were also observed at the distal cervical area of the second premolar tooth. Models with premolar cantilever extensions restored with all-ceramic induced lower Von Mises stress values than metal-ceramic restorations, however models with molar cantilever extensions restored with all-ceramic restorations induced higher Von Misses stress values than metal-ceramic restorations. If the distal cantilever length and restorative material is appropriately chosen, the failure frequency may be reduced. All ceramic can be used as restorative material, when the cantilevers length is not more than the mesiodistal dimension of a premolar tooth and metal-ceramic restorations can be used in longer situations.

Bicuspid↗

PubMed1995

Cancellous bone stresses surrounding the femoral component of a hip prosthesis: an elastic-plastic finite element analysis.

The cancellous bone stresses surrounding the femoral component of total hip replacement were investigated using the finite element method. Four versions of a certain femoral hip prosthesis (the Freeman, Corin Medical), cemented, HA coated, press-fit, and press-fit with ridges were analysed. Each model was subjected to two separate load cases with the cancellous bone modelled as an elastic perfectly plastic material. The effect of bone quality was investigated by varying the cancellous bone stiffness. The resulting cancellous bone stress distributions were compared to that of the intact femur. The results were also compared to clinical subsidence data (published elsewhere) for the Freeman femoral prosthesis to determine if the initial cancellous bone stress distribution could be used to predict the migration of the various versions of this prosthesis. The results showed that the press-fit designs of prosthesis generated substantially higher cancellous bone stresses than the cemented and HA coated designs, and that these stresses were up to 6.5 times higher than found in the intact femur. For all forms of fixation the cancellous bone stress distribution was found to be insensitive to changes in the trabecular bone stiffness: thus poor quality cancellous bone is more likely to promote 'plastic' deformation, and therefore subsidence of the prosthesis. Comparison with the clinical migration data showed a good correlation and revealed that it may be possible to use the calculated initial cancellous bone stresses to predict the migration of the implant, and hence the probability of early and mid-term aseptic loosening.(ABSTRACT TRUNCATED AT 250 WORDS)

Biomechanical Phenomena↗

PubMed1987

Relation of coxarthrosis to stresses and morphogenesis. A finite element analysis.

We calculated subchondral deformations and stresses in the femoral head and acetabulum during weight bearing using finite element models. Areas of high joint contact pressures on the femoral head were shown to correspond to high hydrostatic compression in subchondral bone. The magnitude of the subchondral bone compressive hydrostatic stress correlated with cartilage thickness and was highest in the superior femoral head and moderate at the acetabular roof. The seldom contacting surfaces of the medial-inferior and peripheral areas of the femoral head and the roof of the acetabulum had lower hydrostatic compression and significant subchondral bone tensile strains tangential to the joint surface. Initial cartilage fibrillation and osteophyte formation are often found in these areas. These findings suggest that fluctuating hydrostatic pressure inhibits vascular invasion and the degeneration and ossification of articular cartilage. The generation of tensile strain may promote the degenerative process by direct mechanical mechanisms. Additionally, since tensile strains are associated with a reduction in the compressive hydrostatic stresses in the cartilage and an increase in shear stresses, their presence may permit or promote vascular invasion, cartilage degeneration, and osteophyte formation. These mechanical principles in arthrosis are the same as those that have been previously demonstrated to guide the degeneration and ossification of the cartilage primordium during skeletal morphogenesis. In this sense, arthrosis may be viewed as the final stage in the degeneration and ossification of the cartilage anlage.

Acetabulum↗

PubMed2005

Finite element analysis of a total ankle replacement during the stance phase of gait.

Total ankle replacement (TAR) designs have still several important issues to be addressed before the treatment becomes fully acceptable clinically. Very little is known about the performance, in terms of the contact pressures and kinematics of TAR when subjected to daily activities such as level gait. For this purpose, an explicit finite element model of a novel 3-component TAR was developed, which incorporated a previously validated mechanical model of the ankle ligament apparatus. The intermediate mobile polyethylene meniscal bearing was modelled as an elastic-plastic continuum while the articulating surfaces of the tibial and talar metal components as rigid bodies. Overall kinematics, contact pressures and ligament forces were analysed during passive, i.e. virtually unloaded, and active, i.e. stance phase of gait, conditions. Simulation of passive motion predicted similar kinematics as reported previously in an analytical four-bar linkage model. The meniscal bearing was observed to move 5.6 mm posteriorly during the simulated stance and the corresponding antero-posterior displacement of the talar component was 8.3 mm. The predicted pattern and the amount (10.6 degrees ) of internal-external rotation of the ankle complex were found to be in good agreement with corresponding in vivo measurements on normal ankles. A peak contact pressure of 16.8 MPa was observed, with majority of contact pressures below 10 MPa. For most ligaments, reaction forces remain within corresponding physiological ranges. A first realistic representation of the biomechanical behaviour of the human ankle when replaced by prosthetic joints is provided. The applied methodology can potentially be applied to other TAR designs.

Ankle Joint↗

PubMed1999

Finite element analysis of anterior tooth root stresses developed during endodontic treatment.

Vertical tooth root fractures are diagnostically challenging, frustrating, and an increasingly common cause of failure of tooth restoration. These vertical root fractures have been associated with many causes, including the endodontic process itself. To investigate these endodontic causes, various phases of crown replacement for an anterior tooth were modeled using nonlinear, plane strain finite element (FE) analysis. Stresses developed during obturation, post positioning, crown placement, and masticatory and occlusal loading of the restored tooth were estimated using this analysis method. The minimum (compressive) principal stress was greatest during obturation of cones 1 and 2, and during mastication of the restored tooth. Although these stresses were significant (-150 to -280 MPa), they did not exceed the compressive strength of dentin. The maximum (tensile) principal stresses, 160 to 300 MPa, were also observed during obturation of cones 1 and 2. These peak stresses exceed the dentin tensile strength.

Crowns↗

PubMed2006

[Finite element analysis of the expansion behavior of coronary stents].

Coronary stent is an important device used in Percutaneous Transluminal Coronary Angioplasty (PTCA) which is usually implanted to support the stenosed artery. Its expansion behavior depending on inflating of balloon and characters of recoil happening while the balloon is retrieved is the most important aspects which should be concerned in operation. In this paper, the finite element method was applied to systematically analyze the influence of strut width and thickness and the scale of dilatation of stent on its performance in expansion. The results show that increasing the strut width or thickness can improve the critical internal pressure needed for stent to expand fast. And the change of stent length while expanded is only associated with its structure and final dilatation state. If stent geometry is the same, it is the stent material that may be the main aspect to affect the recoil of stent. Experiment result is well consistent with simulation which indicates that the finite element method can substitute for the stent prototype testing to some extent.

Angioplasty, Balloon↗