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Results for “Finite Element Analysis”

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At least 127 records · Page 7Linked to original sources

PubMed2006

Left ventricular wall stress in patients with severe aortic insufficiency with finite element analysis.

BACKGROUND: Severe aortic insufficiency (AI) with preserved left ventricular (LV) function may be associated with a long asymptomatic period and unpredictable course on medical therapy. Since myocardial wall stress is closely related to both pathologic cardiac remodeling and ultimately to LV decompensation, a more accurate description of regional wall stress may improve our ability to appropriately manage these patients. The objective of this study was to define differences in instantaneous global and regional three-dimensional end-systolic maximum principal stress (ESS) between normal patients and patients with AI, both before and after aortic valve replacement (AVR) using magnetic resonance imaging (MRI) and finite element analysis (FEA). METHODS: Magnetic resonance imaging was performed on 20 normal volunteers and 14 patients with moderate to severe AI with normal systolic function (ejection fraction: 57 +/- 0.6) before and after AVR. Finite element analysis was utilized to estimate global and regional ESS. RESULTS: Both global (p < 0.001) and regional (p < 0.001 in all segments) ESS were significantly higher in the preoperative AI patients when compared with their postoperative values and normal controls. Postoperative ESS was significantly lower than the normal controls (p = 0.002). CONCLUSIONS: Three-dimensional regional and global end-systolic LV wall stress can be determined by MRI and finite element analysis. Values of ESS in patients with chronic AI were elevated prior to AVR and normalized after AVR. This method may have considerable potential as a noninvasive, clinically applicable index of regional LV geometry and function that may help with the serial evaluation of patients with AI.

Adult↗

PubMed2005

[3-Dimensional finite element analysis of single implant-supported prosthesis with three different occlusal designs].

This study was directed at analyzing the stress distribution of the implant in three different models whose cusp inclinations are 45, 35, 25 degrees respectively; the aim was to improve the success rate of implant rehabilitation. The method of is 3-dimensional finite element analysis (3D-FEA) was adopted. A volunteer's mandible was scanned using helix computer tomography and then we got the data of the mandible's margin in digital instrument. ANSYS program files were prepared using these data. Three models were created, meshed, analyzed in computer. Stress concentration was located on the cortical bone around the neck of implant and apical area of implant. Among the three designs, 25 degrees inclination of cusp was appropriate and in such a situation Von Mises stress was minimal.

Biomechanical Phenomena↗

PubMed1998

Evaluating parameters of osseointegrated dental implants using finite element analysis--a two-dimensional comparative study examining the effects of implant diameter, implant shape, and load direction.

Finite element analysis (FEA) has been proven to be a precise and applicable method for evaluating dental implant systems. By means of FEA, a parasaggital model was digitized from a computed tomography (CT)-generated patient data set, and various single-tooth, osseointegrated, two-dimensional dental implant models were simulated. The specific aims of the study were to: (1) examine the effect of implant diameter variation (3.8 mm-6.5 mm) of both a press-fit, stepped cylindrical implant type and a press-fit, straight cylindrical implant type as osseointegrated in the posterior mandible; (2) compare the stress-dissipating characteristics of the stepped implant versus the straight implant design; and (3) analyze the significance of bite force direction (vertical, horizontal, and oblique 45 degrees) on both implant types. The results of the FEA suggested that (1) using the widest diameter implant is not necessarily the best choice when considering stress distribution to surrounding bone, but within certain morphological limits, for both implant types, an optimum dental implant exists for decreasing the stress magnitudes at the bone-implant interface; (2) stress is more evenly dissipated throughout the stepped cylindrical implant when compared to the straight implant type; and (3) it is important in FEA of dental implants to consider not only axial forces (vertical loading) and horizontal forces (moment-causing loads), but also to consider a combined load (oblique bite force), since these are more realistic bite directions and for a given force will cause the highest localized stress in cortical bone. The theoretical analysis performed implies that clinically, whenever possible, an optimum, not necessarily larger, dental implant should be used based on the specific morphological limitations of the mandible and that a stepped cylindrical design for press-fit situations is most desirable from the standpoint of stress distribution to surrounding bone.

Alveolar Process↗

PubMed2003

Finite element analysis of a model of a therapeutic shoe: effect of material selection for the outsole.

The finite element analysis method was used to perform a sensitivity study of the effect of the materials used for the two layers of the outsole (high-density polyethylene, HDPE, and polyurethane, PU) of a "solid rocker-bottom" design of a therapeutic shoe on the responses (stresses and displacements) of a model of the shoe. It was found that the aforementioned materials choice affected the model responses in a noticeable manner. For example, when HDPE was used for the top layer of the outsole, the von Mises stress at the interface between the bottom of the foot and the top layer of the insole ranged from being about 8% lower to being about 62% higher compared to when PU was used. The implications of this finding are discussed.

Computer Simulation↗

PubMed2005

The first metatarsal bone under loading conditions: a finite element analysis.

An individual-based, three-dimensional finite element model of the first metatarsal (MT I) bone was created with fine CT. The three-dimensional model of the bone was fixed proximally at the metatarsocuneiform joint and load was applied on the metatarsal head. Loading conditions were simulated, including muscular forces as described for a normal metatarsophalangeal (MTP) joint during three typical phases of gait as the combination of the load in the contact areas of the sesamoid bones and the base of the proximal phalanx. The resultant strain and stress distributions within the loaded MT I were calculated and visualized with the MTP in different positions.

Adult↗

PubMed2005

Three-dimensional finite element analysis used to compare methods of fixation after sagittal split ramus osteotomy: setback surgery-posterior loading.

We used three-dimensional finite element analysis to compare the biomechanical stability of bilateral sagittal split ramus osteotomies fixed by lag screws with linear and triangular configuration, and double or single six-hole miniplates with monocortical screws after set-back operation. The three-dimensional finite element model contained 122,717 elements and 25,048 nodes. Posterior occlusal loads were simulated on the distal segments. MSC Marc software was used to calculate the stress fields on both the segments and the fixing appliances. We conclude that either triangular lag screw configuration or double miniplates led to better stability and lower mechanical stresses near the osteotomy than the linear lag screws or single oblique miniplates.

Bone Plates↗

PubMed2006

Mode superposition transient dynamic analysis for dental implants with stress-absorbing elements: a finite element analysis.

The purpose of this study was to analyze the dynamic behavior of a dental implant with a stress-absorbing element, using dynamic analysis. Two model types, stress-absorbing model with a resilient stress absorber made of polyoxymethylene and non-stress-absorbing model with rigid titanium, were employed. In both model types, the implant was 4.0 mm in diameter and 13.0 mm in length and placed in the mandibular first molar region. Shapes of the finite element implant and implant-bone were modeled using computer-aided design. All calculations for the dynamic analysis were performed using the finite element method. It was found that the stress-absorbing model had a lower natural frequency than the non-stress-absorbing model. In addition, the stress-absorbing model had a higher damping effect than the non-stress-absorbing model. It was concluded that mode superposition transient dynamic analysis is a useful technique for determining dynamic behavior around dental implants.

Dental Implants↗

PubMed1999

Finite-element-analysis of different screw-diameters in the sagittal split osteotomy of the mandible.

A three dimensional finite element model of the mandible was developed to simulate and study the biomechanical loads of osteosynthesis screws in bilateral sagittal osteotomy. Using the finite-element method clinical conditions were simulated. Different bicortical screw configurations and diameters were evaluated. When bite forces were applied, the most stable configuration was found to be a triangular one. This confirms the results found in the literature. A mini screw of 2.0 mm diameter can provide sufficient stability at the osteotomy site after ramus split osteotomy. Even screws with a diameter of 1.5 mm would withstand forces up to 89.5 N, which would not normally be reached by patients after ramus split osteotomy in the early period of healing. Forces exerted by patients after bilateral ramus split osteotomy do not exceed these values. The finite-element analysis appears to be an adequate method to evaluate this clinical question of interest. It might well replace mechanical models and the results are comparable with those reported in the International literature.

Biomechanical Phenomena↗

PubMed1998

Finite element analysis of static loading in donkey hoof wall.

A finite element model of donkey hoof wall was constructed from measurements taken directly from the hoof capsule of the left forefoot. The model was created with a 2 mm mesh and consisted of 11,608 nodes. A linear elastic analysis was conducted assuming isotropic material properties in response to a 375 newton (N) load, to simulate static loading. The load was applied to the wall via 400 laminae in order to simulate the way in which the pedal bone is suspended within the donkey hoof capsule. Displacement, stress concentration, principal strain, and force distribution across the hoof wall were evaluated. The hoof wall model revealed loading responses that were in broad agreement with previously reported in vivo and modelled observations of the equid hoof. Finite element analysis offers the potential to model hoof wall function at the macroscopic and microscopic level. In this way, it could help to develop further our understanding of the functional relationship between the structural organisation and material properties of the hoof wall.

Animals↗

PubMedDate not supplied

Influence of implant abutment type on stress distribution in bone under various loading conditions using finite element analysis.

PURPOSE: The purpose of this study was to investigate the effect of 3 different abutment types on the stress distribution in bone with inclined loads using finite element analysis. MATERIALS AND METHODS: The 1-body, internal-hex, and external-hex implant systems were modeled to study the effect of abutment type on stress distribution in bone. The bone model used in this study comprised compact and spongious bone assumed to be homogeneous, isotropic, and linearly elastic. RESULTS: In the case of the 1-piece implant, the load was transferred evenly not only in the implant system but also in bone. However, the maximum Von Mises stress generated in bone with the 1-piece implant was always higher than that generated with the internal-hex implant, regardless of load angle inclination. In the case of the internal-hex implant, the contact condition with friction between abutment and implant in the tapered joints and at abutment neck reduced the effect of bending caused by horizontal component of inclined load. The maximum Von Mises stress in bone was the highest for the external-hex implant. DISCUSSION: It was found that the internal-hex implant system generated the lowest maximum Von Mises stresses for all loading conditions because of reduction of the bending effect by sliding in the tapered joints between the implant and abutment. CONCLUSIONS: It was concluded that abutment type has significant influence on the stress distribution in bone because of different load transfer mechanisms and the differences in size of the contact area between the abutment and implant.

Alveolar Process↗

PubMed2005

[Three-dimensional finite element analysis of the stress of mandibular incisor with different level of alveolar bone].

By three-dimensional finite element analysis,the present research inquired about the stress on the surface of alveolar bone of mandibular incisor with different level of bone loss under different loadings. For the mandibular incisor without bone loss, the maximums of the von Mises stress under vertical and 15 degree oblique loading were 13.171 and 14.315 MPa respectively, both located in the apical region, and the lingual displacement of the tooth were 0.056 and 0.197mm respectively; under 30 degree oblique loading, the maximum of the von Mises stress was 15.262 MPa, located not only in the apical region but also on the crest, and the lingual displacement of the tooth was 0.324 mm. However, when vertical loading was applied on the mandibular incisor with half of the alveolar bone loss, the maximum of the stress increased significantly, located in the apical regions. And under oblique loadings, the value of the stress of this model increased dramatically,being three to five times over that of mandibular incisor without bone loss. Both of them concentrated on the crest. The scope of its distribution decreased from area to point. The significant lingual displacement happened, amounting to 2.850 mm. So when the loss of alveolar bone is not less than half,occlusal adjustment and splinting should be considered during the initial treatment of periodontal disease in order to avoid the significant change of the stress and alleviate the damage to the periodontal tissues.

Alveolar Bone Loss↗

PubMed1999

Finite element analysis of the effect of vertical curvature on half-oval cast clasps.

High stresses in half-oval cast clasps are the main causes of deformation or fracture. A vertical curvature in clasps is said to be effective in reducing stress. However, such claims lack scientific basis. The purpose of the present study was to evaluate stress and stiffness in a three-dimensional (3D) finite element analysis (FEA) model of clasps with different vertical curvatures, cross-sectional forms and tapers, and to clarify the effect of vertical curvature on the half-oval cast clasp. Circumferential clasp arms for the mandibular second premolar were analysed by 3D FEA. The clasp arms were approximated by curved cantilever beams with a half-oval cross-section around a cylinder. The radius of curvature was set at 4 mm and the angle subtended by the clasp arm was 120 degrees. The clasp tip was set at a point 2 mm lower than the base. In the 'No-taper' half-oval clasp arm, stress increased and stiffness decreased with the increase in vertical curvature. In the shape of a preformed wax pattern (thickness/width = 0.80, tip/base = 0.70), stress and stiffness decreased slightly. In an 'Original' form (thickness/width = 0.33, tip/base = 0.80), vertical curvature had a very slight effect on stress and stiffness, and stress was the lowest. These findings suggest the superiority of the 'Original' form, with less stress and no effect of vertical curvature.

Dental Casting Technique↗

PubMed2000

The importance of tibial alignment: finite element analysis of tibial malalignment.

The influence of the tibial plateau orientation on cancellous bone stress was examined by finite element analysis for a cemented device. The objectives of the study were i) to examine the effect of the plateau-ankle angle on the cancellous bone stress, ii) to analyze the significance of the anteroposterior angles of the tibial component on these stresses, and iii) to compare the finite element predictions with clinical data. In general, positioning the tibial plateau in valgus resulted in lower cancellous bone stresses. These results support previous clinical studies, which suggest that overall alignment in valgus results in lower migration rates and lower incidence of loosening.

Biomechanical Phenomena↗

PubMed2005

[A three-dimensional finite element analysis for the biomechanical characteristics of orthodontic anchorage micro-implant].

PURPOSE: To establish a three-dimensional finite element model for orthodontic anchorage micro-implant,and to analyze the influence of different titled angles on the biomechanical characteristics of orthodontic anchorage implant-bone interface. METHODS: ANSYS(Analysis System)finite element analysis software was used to perform the finite element modeling of the micro-implant with 7 different tilted angles, including 30 degrees, 40 degrees, 50 degrees, 60 degrees, 70 degrees, 80 degrees and 90 degrees. A simulated orthodontic force, which was 200 grams, was loaded mesiodistally to the mathematical models. The stress and displacement distribution on the implant-bone interface were analyzed. RESULTS: As the titled angle increased, the Von-Mises stress at the cervix of the implants were 1.0792, 1.0104, 0.8848, 0.8181, 0.7583, 0.6339 and 0.5608MPa, while the displacement were 5.5513, 4.9900, 3.7419, 3.1264, 2.5874, 1.3624 and 0.8027microm CONCLUSION: The micro-implant can be safely loaded with 200 grams of mesiodistal orthodontic force. The increase of the titled angle can efficaciously enhance the ability,implicating that the implant can bear a mesiodistal orthodontic force, vertical angle should be chosen when the micro-implant is embedded. Supported by Natural Science Foundation of Liaoning Province (20042076).

Biomechanical Phenomena↗

PubMed2005

Concussion in professional football: brain responses by finite element analysis: part 9.

OBJECTIVE: Brain responses from concussive impacts in National Football League football games were simulated by finite element analysis using a detailed anatomic model of the brain and head accelerations from laboratory reconstructions of game impacts. This study compares brain responses with physician determined signs and symptoms of concussion to investigate tissue-level injury mechanisms. METHODS: The Wayne State University Head Injury Model (Version 2001) was used because it has fine anatomic detail of the cranium and brain with more than 300,000 elements. It has 15 different material properties for brain and surrounding tissues. The model includes viscoelastic gray and white brain matter, membranes, ventricles, cranium and facial bones, soft tissues, and slip interface conditions between the brain and dura. The cranium of the finite element model was loaded by translational and rotational accelerations measured in Hybrid III dummies from 28 laboratory reconstructions of NFL impacts involving 22 concussions. Brain responses were determined using a nonlinear, finite element code to simulate the large deformation response of white and gray matter. Strain responses occurring early (during impact) and mid-late (after impact) were compared with the signs and symptoms of concussion. RESULTS: Strain concentration "hot spots" migrate through the brain with time. In 9 of 22 concussions, the early strain "hot spots" occur in the temporal lobe adjacent to the impact and migrate to the far temporal lobe after head acceleration. In all cases, the largest strains occur later in the fornix, midbrain, and corpus callosum. They significantly correlated with removal from play, cognitive and memory problems, and loss of consciousness. Dizziness correlated with early strain in the orbital-frontal cortex and temporal lobe. The strain migration helps explain coup-contrecoup injuries. CONCLUSION: Finite element modeling showed the largest brain deformations occurred after the primary head acceleration. Midbrain strain correlated with memory and cognitive problems and removal from play after concussion. Concussion injuries happen during the rapid displacement and rotation of the cranium, after peak head acceleration and momentum transfer in helmet impacts.

Brain Concussion↗

PubMed2002

[Design strategy for balloon-expandable stents made of biodegradable polymers using finite element analysis].

Stents made of biodegradable polymers have first been suggested to treat cardiovascular diseases more than ten years ago. Despite the enormous potential of local drug delivery there is no biodegradable coronary stent available today. Some of the problems concern the insufficient mechanical properties of the stent designs. Therefore a design strategy was developed to improve the mechanical properties of balloon-expandable polymer stents. Starting with compiling the possible geometric strut forms we proceeded to design strut features exhibiting an improved deformation behaviour. The addition of functional structures to improve certain stent characteristics led to stent designs, whose mechanical properties, recoil and collaps behaviour, were determined by 3D Finite Element Analysis. Finally, a mechanical in vitro testing of these stent prototypes was conducted.

Absorbable Implants↗

PubMed2002

Finite element analysis on dental implant-supported prostheses without passive fit.

PURPOSE: The purpose of this study is to use finite element analysis to investigate the effect of misfit prostheses, cantilever prostheses, and various occlusal forces on the stress distribution in the prostheses, implant components, and surrounding bone. MATERIALS AND METHODS: Two 3-dimensional finite element models were constructed: (1) a 2-implant-supported, 2-unit fixed partial denture and (2) a 2-implant-supported, 2-unit fixed partial denture with a distal cantilever. Variations of the standard finite element models were made by placing a 111-microm gap between the gold cylinder on either the mesial or distal implant. The effects of load of 100 N were tested on all models. Subsequently, loads of 50 N, 200 N, and 300 N were evaluated on the cantilever model. RESULTS: When the gap was positioned near to the applied force, the stress in both models increased significantly in the implant components and surrounding bone. The stress increase in each component ranged from 8% to 64% in the non-cantilever models and 43% to 85% in the cantilever models. The greatest stress was found in the distal gold screw. The effect of the gap was clearly shown by the pattern of stress distribution in both models. Additionally, the presence of a cantilever and excessive occlusal force amplified the effect of prosthesis misfit. CONCLUSIONS: Prosthesis misfit influenced the pattern and magnitude of stress distribution in the prosthesis, implant components, and surrounding bone, and the presence of the cantilever or greater occlusal force amplified the effect of misfit.

Bite Force↗

PubMed1997

Regional vascular mechanical properties by 3-D intravascular ultrasound with finite-element analysis.

A method employing intravascular ultrasound (IVUS) and simultaneous hemodynamic measurements, with resultant finite element analysis (FEA) of accurate three-dimensional IVUS reconstructions (3-DR), was developed to estimate the regional distribution of arterial elasticity. Human peripheral arterial specimens (iliac and femoral, n = 7) were collected postmortem and perfused at three static transmural pressures: 80, 120, and 160 mmHg. At each pressure, IVUS data were collected at 2.0-mm increments through a 20.0-mm segment and used to create an accurate 3-DR. Mechanical properties were determined over normotensive and hypertensive ranges. An FEA and optimization procedure was implemented in which the elemental elastic modulus was scaled to minimize the displacement error between the computer-predicted and actual deformations. The "optimized" elastic modulus (Eopt) represents an estimate of the component element material stiffness. A dimensionless variable (beta), quantifying structural stiffness, was computed. Eopt of nodiseased tissue regions (n = 80) was greater than atherosclerotic regions (n = 88) for both normotensive (Norm) and hypertensive (Hyp) pressurization: Norm, 9.3 +/- 0.98 vs. 3.5 +/- 0.30; Hyp, 11.3 +/- 0.72 vs. 8.5 +/- 0.47, respectively (mean +/- SE x 10(6) dyn/cm2; P < 0.01 vs. nondiseased). No differences in beta between nondiseased and atherosclerotic tissue were noted at Norm pressurization. With Hyp pressurization, beta of atherosclerotic regions were greater than nondiseased regions: 21.5 +/- 2.21 vs. 14.0 +/- 2.11, respectively (P < 0.03). This method provides a means to identify regional in vivo variations in mechanical properties of arterial tissue.

Arteriosclerosis↗