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At least 397 records · Page 22Linked to original sources
PubMed1999

A fluid--structure interaction finite element analysis of pulsatile blood flow through a compliant stenotic artery.

A new model is used to analyze the fully coupled problem of pulsatile blood flow through a compliant, axisymmetric stenotic artery using the finite element method. The model uses large displacement and large strain theory for the solid, and the full Navier-Stokes equations for the fluid. The effect of increasing area reduction on fluid dynamic and structural stresses is presented. Results show that pressure drop, peak wall shear stress, and maximum principal stress in the lesion all increase dramatically as the area reduction in the stenosis is increased from 51 to 89 percent. Further reductions in stenosis cross-sectional area, however, produce relatively little additional change in these parameters due to a concomitant reduction in flow rate caused by the losses in the constriction. Inner wall hoop stretch amplitude just distal to the stenosis also increases with increasing stenosis severity, as downstream pressures are reduced to a physiological minimum. The contraction of the artery distal to the stenosis generates a significant compressive stress on the downstream shoulder of the lesion. Dynamic narrowing of the stenosis is also seen, further augmenting area constriction at times of peak flow. Pressure drop results are found to compare well to an experimentally based theoretical curve, despite the assumption of laminar flow.

Arteries↗
PubMed2003

Strain distribution within the human femur due to physiological and simplified loading: finite element analysis using the muscle standardized femur model.

The aim of the current work was to study the effect of simplified loading on strain distribution within the intact femur using the Muscle Standardized Femur finite element model and to investigate whether the interaction between the intact human femur and the muscles which are attached to the bone surface could accurately be represented by concentrated forces, applied through the centroids of their attachment areas. An instant at 10 per cent of the gait cycle during level walking was selected as the reference physiological load case; nine load cases were analysed. Comparison of the calculated results for the physiological load case with muscle forces uniformly distributed over their attachment areas showed good agreement with in vivo measurements of strain values and femoral head displacement in humans. Simplified load cases generated unrealistic displacement results and high strain magnitudes, exceeding the physiological range. It was found that when muscles with large attachment areas are included in the model and the muscle forces are simplified, stress and strain distributions will be affected not only on the external bone surface in the vicinity of the load application node, but also on the internal surface of the cortical bone. However, applying muscle forces as concentrated loads at the centroids of the attachment areas can serve as first indicators of the physiological stress and strain levels, if results from nodes and elements in the vicinity of the load application nodes are discarded. Omitting muscle forces or fixing the femur in mid-shaft leads to large unphysiological strain values.

Compressive Strength↗
PubMed2002

[Finite element analysis of shape memory alloy intrasegmental fixator for lumbar spondylolysis].

OBJECTIVE: To study the tensile strength of shape memory alloy intrasegmental fixator and tensile stress distribution in the device during force loading with finite element method (FEM). METHODS: The designed parameters, scanning image, and mechanical properties of shape memory alloy intrasegmental fixator were input into computer for the construction of the FEM model of the device in inherent coordinate of ANSYS. The model was extended with restriction in different parts, and the tensile strength and the distribution of tensile stress in the model was calculated. RESULTS: When the device was loaded with pulling force to induce a relative displacement of 2 mm between the 2 hooks along the two midpoints, the pull was about 281 N, and the tensile stress concentrated more on the middle of device than on the two sides. CONCLUSION: The shape memory alloy intrasegmental fixator is strong enough against tensile stress, which concentrates in the middle portion of the device where fatigue breakage is liable to occur when excessive force is loaded.

Alloys↗
PubMed2005

[3D finite element analysis in consideration of the slide on residual ridge and the rigidity of mandibular complete denture].

PURPOSE: The motions and stress distributions of mandibular complete dentures during use were compared and investigated in terms of denture rigidity using 3D finite element method (FEM) stress analysis. METHODS: Four models for analysis of mandibular complete dentures with different elastic modulus (1. A resin base denture (C), 2. A resin base denture with reinforcement wire (R), 3. A metal base denture (M), 4. A metal plate denture consisting of a double structure (T)) and measured using 3D FEM. Modes were separated into two elastic bodies: the dentures and residual ridge. Analyses were executed under the same conditions total loads of 20 kgf and contact. RESULTS: 1. The total equivalent-potential strain of dentures was high beneath the load point for C and R (2.38 approximately 2.86 x 10(-3)epsilon at buccal-shelf of working side and 0.55 approximately 0.68 x 10(-3)epsilon at posterior residual ridge). The entire dentures barely distorted for M and T (0.98 approximately 1.17 x 10(-3)epsilon at buccal-shelf of working side and 0.21 approximately 0.25 x 10(-3)epsilon at posterior residual ridge). 2. In the main stress distribution of mucosa beneath denture bases, high loads were located beneath the loading point of dentures, at lingual distal areas of the working side in C and R. In M and T, increasing the rigidity of dentures reduced the stress beneath the loading point of dentures. Stress was distributed widely and evenly. CONCLUSIONS: When the rigidity of dentures is high, the strain of dentures decreases, the stress of the residual mucous membrane will evenly become distributed, and the distance of the balancing side from the denture border to the residual mucous membrane at the time of unilateral balanced position will decrease.

Dental Stress Analysis↗
PubMed2005

Three-dimensional finite element analysis of the effect of different bone quality on stress distribution in an implant-supported crown.

STATEMENT OF PROBLEM: Primary implant stability and bone density are variables that are considered essential to achieve predictable osseointegration and long-term clinical survival of implants. Information about the influence of bone quality on stress distribution in an implant-supported crown is limited. PURPOSE: The purpose of this study was to investigate the effect of 4 different bone qualities on stress distribution in an implant-supported mandibular crown, using 3-dimensional (3-D) finite element (FE) analysis. MATERIAL AND METHODS: A 3-D FE model of a mandibular section of bone with a missing second premolar tooth was developed, and an implant to receive a crown was developed. A solid 4.1 x 10-mm screw-type dental implant system (ITI; solid implant) and a metal-ceramic crown using Co-Cr (Wiron 99) and feldspathic porcelain were modeled. The model was developed with FE software (Pro/Engineer 2000i program), and 4 types of bone quality (D1, D2, D3, and D4) were prepared. A load of 300 N was applied in a vertical direction to the buccal cusp and distal fossa of the crowns. Optimal bone quality for an implant-supported crown was evaluated. RESULTS: The results demonstrated that von Mises stresses in D3 and D4 bone quality were 163 MPa and 180 MPa, respectively, and reached the highest values at the neck of the implant. The von Mises stress values in D1 and D2 bone quality were 150 MPa and 152 MPa, respectively, at the neck of the implant. A more homogenous stress distribution was seen in the entire bone. Conclusion For the bone qualities investigated, stress concentrations in compact bone followed the same distributions as in the D3 bone model, but because the trabecular bone was weaker and less resistant to deformation than the other bone qualities modeled, the stress magnitudes were greatest for D3 and D4 bone.

Aluminum Silicates↗
PubMed2006

Efficient 3D finite element analysis of dental restorative procedures using micro-CT data.

OBJECTIVES: This investigation describes a rapid method for the generation of finite element models of dental structures and restorations. METHODS: An intact mandibular molar was digitized with a micro-CT scanner. Surface contours of enamel and dentin were fitted following tooth segmentation based on pixel density using an interactive medical image control system. Stereolithography (STL) files of enamel and dentin surfaces were then remeshed to reduce mesh density and imported in a rapid prototyping software, where Boolean operations were used to assure the interfacial mesh congruence (dentinoenamel junction) and simulate different cavity preparations (MO/MOD preparations, endodontic access) and restorations (feldspathic porcelain and composite resin inlays). The different tooth parts were then imported in a finite element software package to create 3D solid models. The potential use of the model was demonstrated using nonlinear contact analysis to simulate occlusal loading. Cuspal deformation was measured at different restorative steps and correlated with existing experimental data for model validation and optimization. RESULTS: Five different models were validated by existing experimental data. Cuspal widening (between mesial cusps) at 100 N load ranged from 0.4 microm for the unrestored tooth, 9-12 microm for MO, MOD cavities, to 12-21 microm for endodontic access cavities. Placement of an MOD adhesive restoration in porcelain resulted in 100% cuspal stiffness recovery (0.4 microm of cuspal widening at 100 N) while the composite resin inlay allowed for a partial recuperation of cusp stabilization (1.3 microm of cuspal widening at 100 N). SIGNIFICANCE: The described method can generate detailed and valid three dimensional finite element models of a molar tooth with different cavities and restorative materials. This method is rapid and can readily be used for other medical (and dental) applications.

Bite Force↗
PubMed2006

Finite element analysis and stent design: Reduction of dogboning.

In Western countries, cardiovascular disease is the most common cause of death, often related to atherosclerosis. This paper offers a brief introduction into some aspects of this disease and its treatment, where the use of stents is gaining increasing importance. Stents are supporting - mostly metal - tubular mesh structures which are opened in an obstructed artery in order to reopen it, and to offer radial strength to prevent elastic recoil of the dilated vessel. In addition to a variety of experimental tests to study the behavior of (new) stent designs, advanced numerical models (e.g. Finite Element Models) may offer interesting insights in the mechanical behavior of stents and will undoubtedly influence the design of future generation stents. A brief literature review on numerical studies dealing with the mechanical behavior of stents is presented. Subsequently, the finite element method is exploited to investigate and compare different designs of a "first generation" Palmaz Schatz stent in order to reduce the dogboning (i.e. ends of stent open first during expansion) to a minimum. Our computational models (Abaqus ) are described in terms of geometry, constitutive material models, numerical aspects and output quantities. Altering the original symmetric stent design to asymmetric designs decreased the dogboning from 27.24% to less than 10% for the vast majority of the studied asymmetric designs. For one particular configuration, the dogboning effect vanished completely. For this reason, taking asymmetry into account in the design of stents seems very promising, at least from the perspective of dogboning. However, as the dogboning only takes into account the radii (R) at the central and distal part of the stent, nothing can be concluded concerning the uniformity of the complete stent expansion. The mean value (Rm) and the root mean square (R(RMS)) of radii (differences) of the stent at the end of the loading phase (P = 0.7 N/mm2) are much better parameters to give a clear indication of the uniformity of the expanded stent's shape. Although the model is suitable to study basic aspects of stent deployment, further research is necessary, especially accounting for newer generation stent geometries and more realistic balloon-stent interaction.

Angioplasty, Balloon↗
PubMed1996

Finite element analysis of the effect of cantilever and implant length on stress distribution in an implant-supported fixed prosthesis.

This study investigated the stress distribution at the bone/implant interface with a three-dimensional finite element stress analysis by using three different cantilever and implant lengths in an implant-supported fixed partial denture. Simulation models were created as a bilateral distal cantilever fixed partial denture supported with six implants embedded in a model of the mandibular bone. Nine different simulation models had three different cantilevers (7, 14, and 28 mm) and implant lengths (7, 15, and 20 mm). Vertical forces of 75 N and horizontal forces of 25 N were applied to the distal end of the cantilever. Analysis of the von Mises stresses for the bone/implant interfaces revealed that the maximum stresses occurred at the most distal bone/ implant interface located on the loaded side and significantly increased with the length of the cantilever. However, there was no statistically significant change associated with the length of implants.

Computer Simulation↗
PubMed2001

[Finite element analysis of pulsatile flow in aortic arch].

The blood flows in the ascending aorta and the aortic arch are studied. The theoretical models, boundary conditions and calculation conditions are proposed. The numerical simulation with finite element method of the blood flow in aortic arch of dogs is carried out according to the physiologically pulsatile flow conditions. The calculation results are analyzed with scientific visualization method.

Animals↗
PubMed2002

Finite element analysis and fatigue of stents.

Understanding the behaviour of implantable medical devices is of obvious importance. The potential for failure of a medical device can often be associated with issues related to cyclic loading of the device, and material fatigue. Detailed finite element simulations to evaluate the fatigue of stents allow the engineer to assess potential failures. The engineer can then use the analysis results to modify the design and prevent failure, without making and testing numerous physical devices. Complete understanding of the mechanical behaviour of a stent provided by finite element analysis has the benefits of facilitating effective design, helping to reduce time to market and minimising the potential for unwanted failures.

Journal Article↗
PubMed1988

A nonlinear finite element analysis of interface conditions in porous coated hip endoprostheses.

We used a geometrically simplified finite element model to investigate load transfer between a porous coated hip endoprosthesis and a femur. Assuming both rigidly bonded and nonlinear interfaces, we analyzed fully and partially coated stems that had coatings of different elastic moduli. Our results indicate that maximum values for relative motion in the interface between bone and implant occur for implants with the same elastic modulus as compact bone. By comparison, interface motion is reduced by about half for Co-Cr-Mo alloy stems. We also showed that the elastic modulus of the porous coating had only a small influence on bone stresses.

Biomechanical Phenomena↗
PubMedDate not supplied

Selection of the best element type in the finite element analysis of hip prostheses.

Hip prostheses have to fulfil biomedical, anatomical and strength requirements. In the initial design phase it is convenient to carry out contact analyses that simulate standardized fatigue tests using automatically generated finite element meshes of the implant design. While parabolic tetrahedrons are known to be more accurate, they usually cannot be used in contact analyses. In the present study, a prototype design was analysed using automatically generated tetrahedral meshes under linearly equivalent boundary conditions. Results of convergence analyses show that linear tetrahedral elements, even with rotational degrees of freedom, should be avoided, especially when modelling regions with a high stress gradient.

Biomechanical Phenomena↗
PubMed1990

A dynamic finite element analysis of impulsive loading of the extension-splinted rabbit knee.

A dynamic nonlinear finite element model was developed to study juxtarticular stresses in the splinted rabbit knee, an established laboratory model for creating osteoarthrosis due to impulsive loading. Plane strain finite element results were validated by comparison with corresponding experimental data. Parametric effects studied included the input tibial displacement speed, the local bone density distribution, and the modulus of cartilage and subchondral bone. While the computed resultant contact force magnitude was sensitive to a number of model parameters, the stress patterns, when normalized to a given resultant force magnitude, were not. Despite comparable force peaks, the finite element results showed approximately six-fold higher effective strain rate levels for a severely impulsive loading protocol known to induce rapid osteoarthrosis, versus those for a mildly impulsive loading protocol not usually associated with cartilage damage. A propensity for elevated shear in the deep cartilage layer near the contact periphery, observed in nearly all computed stress distributions, is consistent with previous experimental findings of fissuring at that level in the impulsively loaded rabbit knee.

Animals↗
PubMed1997

[Finite element analysis of force produced by "T" loop retraction archwire].

This study introduced three presumed springs to imitate the three dimensional bolstering function of the bracket-tooth-periodontal tissue on the archwire with three dimensional finite element method (FEM), and, systematically analysed the force system produced by the "T" loop retraction archwire on the incisors. The following conclusions were drawn; (1) The activation of the "T" loop retraction archwire will produce extrusion and root lingual torque force as well as horizontal force on the incisors; (2) Adequate torqul on the incisor segment and gable bend mesial to the T-loop are necessary to control the position of the anterior teeth while they are being retracted; (3) retraction archwire should not be activated too much; (4) Lighter wire will produce milder and more durable forces.

Biomechanical Phenomena↗
PubMedDate not supplied

Interdental design of porcelain veneers in the presence of composite fillings: finite element analysis of composite shrinkage and thermal stresses.

PURPOSE: This study was conducted to optimize the interdental design (wraparound) of porcelain laminates bonded to teeth in the presence of preexisting composite fillings. MATERIALS AND METHODS: A finite element model (2-dimensional mesh generated from a horizontal cross section of a maxillary incisor) was used to evaluate the effects of luting composite shrinkage and thermal changes on the stress distribution within the ceramic. The mesh included 3 restorative designs (3 degrees of interdental wrapping) and a Class III composite filling. Curing contraction of the luting composite was simulated at baseline temperature (37 degrees C). Thermal loads from 37 to 60 degrees C and from 37 to 5 degrees C were assessed with and without preexisting composite shrinkage. Surface tangential stresses were calculated at the ceramic surface and interface. RESULTS: Curing contraction alone generated mostly compressive stresses (peaks at 15 MPa) at both the ceramic surface and interface. Stresses remained compressive (peaks at 20 MPa) when thermal changes were added, except for the conservative veneer with minimum wraparound, the margins of which showed potentially harmful tensile stress peaks (approximately 7 MPa). Deformation of the tooth-restoration complex tended to be more uniform for veneers with maximum wraparound. In the presence of thermal loads alone, opposite effects were observed on the restoration surface and the interface, with compressive stresses on one side (up to 13 MPa) and tensile stresses on the other (up to 9 MPa). This effect of proximal bending (explained by the nearby expansion/contraction of the composite filling) was attenuated by the significant reduction of the bulk of the preexisting interdental composite by the overlapping veneer. CONCLUSION: In the finite element environment, the negative effect of the nearby expanding/contracting composite fillings can be minimized by extending the veneer over the preexisting interdental restoration. Because of the precompressed state resulting from composite shrinkage, ceramics showed lower temperature-induced tensile stresses.

Composite Resins↗
PubMed2001

Fabrication of a functionally graded dental composite resin post and core by laser lithography and finite element analysis of its stress relaxation effect on tooth root.

Laser lithography was applied for Computer Aided Design and Computer Aided Manufacturing (CAD/CAM) fabrication of dental prostheses made of composite resin. First, the conditions to obtain the optimum resolution for photo-curing were determined, and then a composite resin full crown was fabricated by laser lithography. Second, a functionally graded composite resin post and core which had gradient elasticity in the post, was manufactured by the gradual change in the filler contents of the composite resin. Finally, stress analysis of the functionally graded post and core was performed by a two-dimensional finite element method. This demonstrated the effects of reducing the stress concentration around the apex of the post.

Composite Resins↗