Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Finite Element Analysis”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 901 records · Page 50Linked to original sources
PubMedDate not supplied

Finite element stress analysis of a class I amalgam restoration subjected to setting and thermal expansion.

Stress analyses are presented for a second mandibular premolar with a class 1 amalgam restoration. The effects of amalgam setting and thermal expansions are examined. An axisymmetric representation of the structure is used and the analyses are carried out by the finite element method. Lined and unlined restorations are compared with regard to the principal stresses set up in the composite structures and also the patterns of deformation incurred. The effects of various enamel and dentin stiffness combinations are also considered.

Chemical Phenomena↗
PubMed2002

[Three dimensional finite element stress analysis in various class II cavity design on first maxillary premolar].

OBJECTIVE: To evaluate the stress influence in different contour of class II cavity with different filling materials on first maxillary premolar. METHODS: The stress distribution in two types and all three contours of class II cavity in maxillary premolar were analyzed by three dimensional finite element. The cavity was respectively filled with amalgam and composite resin; and the vertical and lateral stress force was calculated. RESULTS: In the different contours, the stress of composite restoration by slot design was close to that by dovetail design, and the stress of amalgam restoration by slot design, especially in vertical force, descended respectively at 41%,29% and 27%. CONCLUSION: When class II lesions is only limited in proximal region of the premolar, the filling of composite resin with slot design is recommended.

English Abstract↗
PubMedDate not supplied

The effect of a hydroxyapatite-reinforced polyethylene stress distributor in a dental implant on compressive stress levels in surrounding bone.

This study investigated various designs of stress breakers incorporated into the dental implant using 3-D finite element analysis. These designs employed hydroxyapatite-reinforced polyethylene (HRP), a material capable of inducing osseointegration. The most successful design was that of a dental implant with a peripheral HRP component that was in direct contact with the bone surrounding the neck of the implant. This design lowered the compressive stress values in bone around the neck of the implant. Attempts were also made to optimize this design.

Alveolar Process↗
PubMed2006

The effect of necrotic lesion size and rotational degree on the stress reduction in transtrochanteric rotational osteotomy for femoral head osteonecrosis--a three-dimensional finite-element simulation.

BACKGROUND: The prospect for success in the efficacy of osteotomy for precollapse stage of femoral head osteonecrosis depends on the ability to predict reliably the stress changes derived from specific osteotomies. A three-dimensional finite-element analysis was thus designed to compute necrotic femoral head stress changes with different extent of necrocrosis that accompany anterior or posterior rotational osteotomies. METHOD: Computed tomography images of a standard composite femur were used to create the three-dimensional finite-element intact femur model. Based on the intact model, 27 models simulating three different levels of necrotic region together with nine different rotational osteotomies were created. The von Mises stress distributions of each model were analyzed and compared for a loading condition simulating single-legged stance. FINDINGS: (1) The stress reduction in anterior rotational osteotomy is more effective as compared to that of the posterior rotational osteotomy for various necrotic lesion sizes. (2) Von Mises stress on the necrotic zone decreased with increasing rotational angle. The decreasing rate was higher for the femoral head with a narrow lesion. (3) Femoral head with a wider necrotic lesion had a higher risk for developing collapse due to high local stress on the surface of necrotic region; whereas the necrotic region tended to expand in size instead of collapse for femoral head with a narrow lesion due to high local stress on the interface between necrotic region and healthy bone. INTERPRETATION: Transtrochanteric rotational osteotomy is a technically demanding procedure and associated with high complication risks, a more scrupulous planning including the finite-element analysis should be considered before doing surgery in clinical subjects.

Femur Head↗
PubMed2000

Influence of muscular activity on local mineralization patterns in metatarsals of the embryonic mouse.

This study addressed the theory that local mechanical loading may influence the development of embryonic long bones. Embryonic mouse metatarsal rudiments were cultured as whole organs, and the geometry of the primary ossification center was compared with that of rudiments that had developed in utero. The mineralization front in vivo was found to be nearly straight, whereas in vitro it acquired a more convex shape due to a slower mineralization rate at the periphery of the mineralized cylinder. A poroelastic finite element analysis was performed to calculate the local distributions of distortional strain and fluid pressure at the mineralization front in the metatarsal during loading in vivo as a result of muscle contractions in the embryonic hindlimbs. The distribution of fluid pressure from the finite element analysis could not explain the difference in mineralization shape. The most likely candidate for the difference was the distortional strain, resulting from muscle contraction, which is absent in vitro, because its value at the periphery was significantly higher than in the center of the tissue. Without external loads, the mineralization process may be considered as pre-programmed, starting at the center of the tissue and resulting in a spherical mineralization front. Strain modulates the rate of the mineralization process in vivo, resulting in the straight mineralization front. These results confirm that disturbances in muscle development are likely to produce disturbed mineralization patterns, resulting in a disordered osteogenic process.

Animals↗
PubMed1993

Nonlinear finite element contact analysis of dental implant components.

The treatment design of most dental restorations is largely empirical and based on the experience of the individual practitioner. Because the biomechanical aspects of implant-supported restorations are difficult to assess on an individual basis, there is a possibility for compromised biomechanical performance of the implant-retained restoration to achieve satisfactory esthetics and phonetics. Through repeated loading cycles, the restoration or its components may fatigue and fail. This study evaluated the biomechanical behavior of the crown component relative to the gold retaining screw and abutment under load to provide insight into the mechanism of loosening and fracture of the retaining screw. A two-dimensional finite element model of the dental implant components was developed for nonlinear contact analysis. A simulation of tightening of the retaining screw was followed by axial loading of a cusp tip on the implant-supported crown. Loading of the cusp tip resulted in separation of the contact between (1) the gold retaining screw and abutment, and (2) the crown and the abutment. Repeated loading and unloading cycles resulted in alternating contact and separation between the retaining screw head base and the crown. Clinical findings of screw loosening and failure probably result from these separation events and from elevated strains in the screw as demonstrated by the model.

Crowns↗
PubMed2004

Geometric and material nonlinearity in tensioned wires of an external fixator.

OBJECTIVE: To investigate the fundamental characteristics of a tensioned wire in an external fixator. DESIGN: Many factors that may influence the wire performance including the change in wire geometry, material hardening and yielding, loading and unloading, and levels of pre-tension are considered in order to obtain a whole spectrum of the wire characteristics. BACKGROUND: External fixation is widely used in the treatment of unstable fractures, limb lengthening, and congenital and pathological orthopedic deformities. With the use of tensioned wires, external fixation provides attractive features such as minimal invasiveness, maximum tailorability, and versatility. These seemingly simple wires actually fulfill a very complex duty. To be able to maximize the benefit of these wires, it is necessary to know their fundamental characteristics. METHODS: A single wire was isolated from an external Ilizarov ring-frame, and nonlinear elastic and plastic analyses of the wire were performed using the method of finite element analysis. RESULTS: The nonlinear behavior of the wire originates not only from the material hardening and yielding but also from the change in its geometry. Pre-tension reduces wire deflection, delays the onset of full-plastic deformation, and elevates the limiting plastic moment, but at the same time leads to early material hardening and yielding. CONCLUSIONS: An entire load-deflection curve is necessary when comes to describe the wire performance. To enhance the wire performance, further efforts should be directed to exploiting the benefit of geometric nonlinearity of the wire. RELEVANCE: The findings will lead to refinement of external fixation design and provide engineering information to surgeons regarding the application of pre-tension during surgery.

Bone Wires↗
PubMed1992

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)

Computer Simulation↗
PubMed1995

Fracture toughness determination of dental materials by laboratory testing and finite element models.

This study assessed the effectiveness of finite element analysis in predicting the stress intensity factor (KIC) for three types of dental materials: a glass ionomer, a dental amalgam, and a composite resin. Laboratory tests were conducted on small single-edge notch specimens loaded in three-point bending to determine values for fracture toughness (KQ). Using the dimensions measured for each laboratory specimen, a J integral approach was employed to calculate KIC using finite element analysis. Both two-dimensional plane strain and three-dimensional models were used in determining KIC for each specimen, and these values were compared to the KQ values obtained from laboratory tests. The results indicated that no significant differences existed between laboratory results and those obtained from both two- and three-dimensional finite element models (P > .85). For the three-dimensional model, values for KIC were found to vary across the specimen thickness, with the values at the center of the specimen closely paralleling those obtained from the two-dimensional plane strain model. It was concluded that the two-dimensional plane strain J integral technique was as effective as the three-dimensional technique in calculating values for KIC.

Dental Materials↗
PubMed2001

Finite element tension analysis of the supporting tissues of a maxillary canine.

INTRODUCTION: The distribution of masticatory load on the teeth and the arising force tensions in them are factors that determine the origine of destructive processes in their periodontium. The development of mathematical models and application of new computer technologies make possible their precise study. They are still not thoroughly studied. PURPOSE: To study the tensions, originating in the periodontium of a canine tooth during occlusal load by the modern method of finite elements (MFE). MATERIALS AND METHODS: A three-dimensional model of a maxillary canine is built by MFE containing 304 finite elements with six varieties of geometrical form, linked in 1409 nodes. It is supposed that the tooth is fixed firmly to the outer surface of the periodontal membrane to the alveolar bone and is loaded in the lingual wall by a force perpendicular to its longitudinal axis and directed from the lingual to the vestibular wall. RESULTS: As a result of the calculations according to MFE the tension state of dental tissues is calculated for diferent degrees of destruction of the alveolar bone. It was established that with the increase of destruction of the alveolar bone for one and the same masticatory load, the tensions in the periodontal membrane also increase. The maximal tensions act in the apex of the root and around the clinical neck of the teeth. CONCLUSION: The results obtained provide precise information of distribution of force tensions in the periodontium of maxillary canines during occlusal load. They serve as a serious theoretical base for future investigations.

Cuspid↗
PubMed2002

Miniature specimen shear punch test for UHMWPE used in total joint replacements.

Despite the critical role that shear is hypothesized to play in the damage modes that limit the performance of total hip and knee replacements, the shear behavior of ultra-high molecular weight polyethylene (UHMWPE) remains poorly understood, especially after oxidative degradation or radiation crosslinking. In the present study, we developed the miniature specimen (0.5 mm thickness x 6.4mm diameter) shear punch test to evaluate the shear behavior of UHMWPE used in total joint replacement components. We investigated the shear punch behavior of virgin and crosslinked stock materials, as well as of UHMWPE from tibial implants that were gamma-irradiated in air and shelf aged for up to 8.5 years. Finite element analysis, scanning electron microscopy, and interrupted testing were conducted to aid in the interpretation of the shear punch load-displacement curves. The shear punch load-displacement curves exhibited similar distinctive features. Following toe-in, the load-displacement curves were typically bilinear, and characterized by an initial stiffness, a transition load, a hardening stiffness, and a peak load. The finite element analysis established that the initial stiffness was proportional to the elastic modulus of the UHMWPE, and the transition load of the bilinear curve reflected the development of a plastically deforming zone traversing through the thickness of the sample. Based on our observations, we propose two interpretations of the peak load during the shear punch test: one theory is based on the initiation of crystalline plasticity, the other based on the transition from shear to tension during the tests. Due to the miniature specimen size, the shear punch test offers several potential advantages over bulk test methods, including the capability to directly measure shear behavior, and quite possibly infer ultimate uniaxial behavior as well, from shelf aged and retrieved UHMWPE components. Thus, the shear punch test represents an effective and complementary new tool in the armamentarium of miniature specimen mechanical testing methods for UHMWPE used in total joint replacement components.

Arthroplasty, Replacement↗
PubMed2006

Analysis of mechanical stress in reconstruction plates for bridging mandibular angle defects.

INTRODUCTION: The objective of the present study was to evaluate the mechanical stress in reconstruction plates and the screw-plate-bone interface used in bridging a mandibular angle defect by means of the finite element method (FEM). The influence of plate geometry as well as the configuration and the diameter of the screws on the mechanical stress distribution was to be determined at the same time and was used as the basis for developing suggestions to optimize the design of the reconstruction plates. MATERIAL: Based on the geometrical data of a human mandible, an angle defect bridged by a titanium reconstruction plate was generated and exposed to chewing force. First a reconstruction plate was tightly fixed with M2.7 titanium screws. Then, plate design, screw configuration and screw diameter were varied. The mechanical stress was calculated according to von Mises stress hypothesis. RESULTS: In the standard reconstruction plate, the result of the finite element analysis revealed stress resulting from the simulated functional loadings which far exceeded the strengths of the components. Possible clinical consequences could be a fatigue fracture of the plate itself, gradual loosening of the osteosynthesis screws and loss of bone. The stress can be reduced to less than half by increasing the diameter of the screw threads 1.5 fold. CONCLUSION: Maximizing the interface between bone and reconstruction plate had a favourable effect. As a consequence of the large interface and a triangular or square configuration of the screws, the stresses could be substantially reduced, the plate could be made thinner and thus better adapted to the mandible. As a preliminary result, the newly designed reconstruction plate could be thinned in areas subject to less mechanical stress.

Bite Force↗
PubMed1996

Finite element stress analysis of a hybrid fracture fixation plate.

Metal plates are commonly used in the operative treatment of bone fractures. Rigid metal plates stabilize the fracture site, maintain good contact between bone fragments and allow early weight bearing and patient mobility. However, treatment with rigid metal plates can cause localized bone atrophy due to stress-shielding and interference with blood circulation, and the weakened bone can refracture after plate removal. A hybrid bone plate system that combines the torsional and bending rigidity of a metal plate with the axial compliance of a polymer insert has been designed. A three-dimensional, quarter-symmetric finite element model was generated for a canine femur diaphysis plated with this metal/polymer hybrid design. A model with a standard metal fixation plate was also generated for comparison purposes. The stress state in the underlying bone was examined for several loading conditions taken from published in vivo studies. The finite element model was used to study the performance of biodegradable polymer inserts in the plate system. The flexible plate reduced stress-shielding effects at the fracture site when subjected to an axial load. The bending strength of the plate was not compromised by the addition of the polymer inserts. Biodegradable inserts further enhanced the performance of the new plate design, transferring less of the axial load to the plate as the inserts broke down.

Animals↗
PubMed2001

Design improvement of the jellyfish valve for long-term use in artificial hearts.

In a previous communication, we reported a leaflet fracture in a Jellyfish valve that was incorporated into a blood pump, after a 312-day animal implant duration. Subsequent finite element analysis revealed that the fracture location was consistent with an area of maximum strain concentration. Therefore, the aim of this study was to improve the durability in the light of these findings. Based on the engineering analysis results, a new valve seat having a concentric ring of 0.5-mm width, located at a radius of 7.0 mm, was designed and fabricated. Accelerated fatigue tests, conducted under the conditions recommended by ISO 5840, demonstrated that the durability of this new prototype was extended by a factor of 10, as compared to the original valve. Moreover, further finite element analysis indicated that the maximum equivalent elastic strain of the proposed new valve was reduced by 52.3% as compared to the original valve. Accordingly, it has been confirmed that the modified Jellyfish valve is suitable for use in long-term artificial hearts.

Heart Valve Prosthesis↗
PubMed1995

Role of ligaments and facets in lumbar spinal stability.

STUDY DESIGN: The issue of segmental stability using finite element analysis was studied. Effect of ligament and facet (total and partial) removal and their geometry on segment response were studied from the viewpoint of stability. OBJECTIVES: To predict factors that may be linked to the cause of rotational instabilities, spondylolisthesis, retrospondylolisthesis, and stenosis. SUMMARY OF BACKGROUND DATA: The study provides a comprehensive study on the role of facets and ligaments and their geometry in preserving segmental stability. No previous biomechanical study has explored these issues in detail. METHODS: Three-dimensional nonlinear finite element analysis was performed on L3-L4 motion segments, with and without posterior elements (ligaments and facets), subjected to sagittal moments. Effects of ligament and facet (partial and total) removal and their orientations on segment response are examined from the viewpoint of stability. RESULTS: Ligaments play an important role in resisting flexion rotation and posterior shear whereas facets are mainly responsible for preventing large extension rotation and anterior displacement. Facet loads and stresses are high under large extension and anterior shear loading. Unlike total facetectomy, selective removal of facets does not compromise segmental stability. Facet loads are dependent on spatial orientation. CONCLUSIONS: Rotational instability in flexion or posterior displacement (retrospondylolisthesis) is unlikely without prior damage of ligaments, whereas instability in extension rotation or forward displacement (spondylolisthesis) is unlikely before facet degeneration or removal. The facet stress and displacement distribution predicts that facet osteoarthritis or hypertrophy leading to spinal stenosis is most likely under flexion-anterior shear loading. Selective facetectomy may restore spinal canal size without compromising the stability of the segment. A facet that is more sagittally oriented may be linked to the cause of spondylolisthesis, whereas a less transversely oriented facet joint may be linked to rotational instabilities in extension.

Biomechanical Phenomena↗
PubMed2001

Biological reactions of alveolar bone to orthodontic loading of oral implants.

Enosseous oral implants have been suggested as anchorage for orthodontic appliances in cases where the existing dentition cannot provide sufficient stability. Long-term studies of oral implants have suggested that excessive loading may contribute as an etiologic factor in the pathogenesis of failing implants. The purpose of the present study was to perform a histomorphometric analysis of tissue reactions around implants subjected to a well-defined force system. The analysis was performed on undecalcified sections cut perpendicularly to the long axis of the implant. The degree of osseointegration, bone density at varying distances from the implant as well as the relative extent of resorption and formation of alveolar bone adjacent to the implant-bone interface were evaluated. The results were correlated with the local strain of the tissue estimated by the means of a finite element analysis. It was found that loading significantly influenced both the turnover and the density of the alveolar bone in the proximity of the implants. However, even unloaded implants tended to maintain the bone characteristics of the alveolar process. On the other hand, the degree of osseointegration appeared to be independent of the loading of the implant.

Alveolar Process↗
PubMed2002

MRI gradient coil cylinder sound field simulation and measurement.

High-field, high-speed Magnetic Resonance Imaging (MRI) generates high sound levels within and nearby the scanner. The mechanism and process that produces the gradient magnetic field (a cylindrical electro-magnet, called the gradient coil cylinder, which produces a spatially and temporally varying magnetic field inside a static background magnetic field) is the primary source of this noise. This noise can cause difficulties in verbal communication in and around the scanner, heightened patient anxiety, temporary hearing loss and possible permanent hearing impairment for health care workers and patients. In order to effectively suppress the sound radiation from the gradient coil cylinder the sound field within and nearby the gradient coil needs to be characterized This characterization may be made using an analytical solution of the sound pressure field, computational simulation, measurement analysis or some combination of these three methods. This paper presents the computational simulation and measurement results of a study of the sound radiation from a head and neck gradient coil cylinder within a 4 Tesla MRI whole body scanner. The measurement results for the sound pressure level distribution along the centerline of the gradient coil cylinder are presented. The sound pressure distributions predicted from Finite Element Analysis of the gradient coil movement during operation and subsequent Boundary Element Analysis of the sound field generated are also presented. A comparison of the measured results and the predicted results shows close agreement. Because of the extremely complex nature of the analytical solution for the gradient coil cylinder, a treatment of the analytical solution and comparison to the computational results for a simple cylinder vibrating in a purely radial direction are also presented and also show close agreement between the two methods thus validating the computational approach used with the more complex gradient coil cylinder.

Computer Simulation↗