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PubMedDate not supplied

Hand-held, dynamic indentation system for measuring myocardial transverse stiffness.

Primary muscle abnormalities and/or alterations in regional loading may be critical in myocardial infarct expansion and remodeling, cardiomyopathy progression, and arrhythmia generation. To differentiate muscle abnormalities from loading abnormalities, an estimation of regional wall stress is needed. Researchers have previously relied on geometric models and finite element analysis to estimate wall stress, but these estimations have not been validated. It has been shown that the transverse stiffness (the ratio of indentation stress to indentation strain during transverse indentations) of a cardiac muscle can be used to estimate the myocardial wall stress. The authors designed and tested a hand-held dynamic indentation system that can determine the regional transverse stiffness of an intact heart in as little as 15 milliseconds, allowing multiple estimations of wall stress over a single contraction cycle. The sensor was validated with a finite-element analysis of the indentation process, as well as with direct measurements on isolated heart muscle, and on soft, nonbiologic materials. The validations confirmed that the dynamic indentation system does accurately estimate myocardial wall stress. This regional-wall-stress sensor could help to enhance the understanding of cardiac pathophysiology, guide therapy, and assist surgeons in planning cardiac surgeries.

Cardiac Surgical Procedures↗
PubMed1993

Design of a composite monocoque frame racing wheelchair.

Design of present-day racing wheelchairs developed out of necessity and common sense. The chairs first used in racing were everyday chairs; through years of trial and modification the racing chairs of today evolved. Very little advanced engineering has been applied to the design of racing chairs. The Finite Element Analysis model executed on a computer provided insight into structural problem areas in the design of unibody frame racing chairs. Slight modifications to the model can be used to investigate new shapes, loads, or materials without investing large amounts of time and money. Wind tunnel testing with scale models provided perspectives on different improvements to reduce drag. Shape improvements may play an important role in reducing the racer's time during competition. Shape may help to decrease drag for the user in either the upright or down position. Considering that the frontal area increases around 30% in the up position with current strut and chassis frames, monocoque shapes should excel. Finite element analysis and air drag analysis are important to the design of a composite racing wheelchair. Composite materials may promote more efficient and ergonomic racing wheelchairs.

Computer Simulation↗
PubMed2003

Finite element modeling of the human thoracolumbar spine.

STUDY DESIGN: Biomechanical properties within cadaveric vertebral bodies were parametrically studied using finite element analysis after calibration to experimental data. OBJECTIVES: To develop and validate three-dimensional finite element models of the human thoracolumbar spine based on quantitative computed tomography scans. Specifically, combine finite element modeling together with biomechanical testing circumventing problems associated with direct measurements of shell properties. SUMMARY OF BACKGROUND DATA: Finite element methods can help to understand injury mechanisms and stress distribution patterns within vertebral bodies as an important part in clinical evaluation of spinal injuries. Because of complications in modeling the vertebral shell, it is not clear if quantitative computed tomography-based finite element models of the spine could accurately predict biomechanical properties. METHODS: We developed a novel finite element modeling technique based on quantitative computed tomography scans of 19 radiographically normal human vertebra bodies and mechanical property data from empirical studies on cylindrical trabecular bone specimens. Structural properties of the vertebral shell were recognized as parametric variables and were calibrated to provide agreement in whole vertebral body stiffness between model and experiment. The mean value of the shell properties thus obtained was used in all models to provide predictions of whole vertebral strength and stiffness. RESULTS: Calibration of n = 19 computer models to experimental stiffness yielded a mean effective modulus of the vertebral shell of 457 +/- 931 MPa ranging from 9 to 3216 MPa. No significant correlation was found between vertebral shell effective modulus and either the experimentally measured stiffness or the average trabecular modulus. Using the effective vertebral shell modulus for all 19 models, the predicted vertebral body stiffness was an excellent predictor of experimental measurements of both stiffness (r2= 0.81) and strength (r2 = 0.79). CONCLUSION: These findings indicate that modeling of the vertebral shell using a constant thickness of 0.35 mm and an effective modulus of 457 MPa, combined with quantitative computed tomography-based modeling of trabecular properties and vertebral geometry, can accurately predict whole vertebral biomechanical properties. Use of this modeling technique, therefore, should produce substantial insight into vertebral body biomechanical behavior and may ultimately improve clinical indications of fracture risk of this cohort.

Adult↗
PubMed1996

Stress concentration in all-ceramic posterior fixed partial dentures.

Two-dimensional finite-element analysis was used to study levels and distribution patterns of stress within three-unit fixed partial dentures (mandibular first premolar to first molar) constructed of different materials (Type III gold alloy, Dicor, and In-Ceram) and with different connector heights (3.0 mm versus 4.0 mm). In the computer models, 10 MPa of stress was applied centrally to the prosthesis. Resultant von Mises stresses were concentrated within the connectors; the greatest stress occurred at the axial location of the connector. Stresses were 40% to 50% lower for 4.0-mm connectors. Patterns of stress distribution were similar for premolar and molar connectors. Stress levels within In-Ceram models were lower than for the other two materials and represented a lower percentage of the ultimate strength of the material. Based on a two-dimensional finite-element analysis model, In-Ceram would appear to be the best choice for posterior fixed partial dentures.

Aluminum Oxide↗
PubMed2004

CT-based geometry analysis and finite element models of the human and ovine bronchial tree.

The interpretation of experimental results from functional medical imaging is complicated by intersubject and interspecies differences in airway geometry. The application of computational models in understanding the significance of these differences requires methods for generation of subject-specific geometric models of the bronchial airway tree. In the current study, curvilinear airway centerline and diameter models have been fitted to human and ovine bronchial trees using detailed data segmented from multidetector row X-ray-computed tomography scans. The trees have been extended to model the entire conducting airway system by using a volume-filling algorithm to generate airway centerline locations within detailed volume descriptions of the lungs or lobes. Analysis of the geometry of the scan-based and model-based airways has verified their consistency with measures from previous anatomic studies and has provided new anatomic data for the ovine bronchial tree. With the use of an identical parameter set, the volume-filling algorithm has produced airway trees with branching asymmetry appropriate for the human and ovine lung, demonstrating the dependence of the method on the shape of the lung or lobe volume. The modeling approach that has been developed can be applied to any level of detail of the airway tree and into any volume shape for the lung; hence it can be used directly for different individuals or animals and for any number of scan-based airways. The resulting models are subject-specific computational meshes with anatomically consistent geometry, suitable for application in simulation studies.

Algorithms↗
PubMed2001

Modeling and underwater characterization of cymbal transducers and arrays.

The cymbal is a miniaturized class V flextensional transducer that was developed for potential use as a shallow water sound projector and receiver. Single elements are characterized by high Q, low efficiency, and medium power output capability. Its low cost and thin profile allow the transducer to be assembled into large flexible arrays. Efforts were made to model both single element and transducer arrays by coupling finite element analysis (ATILA) and the integral equation formulation (EQI). The pressure and velocity distributions on the surface elements were calculated by ATILA and later used with EQI to calculate the far field properties of the transducer element and arrays. It eliminates the mesh of the fluid domain and makes the 3-D model of a transducer possible. Three-dimensional models of a cymbal transducer and a 3 x 3 cymbal array were developed in the modeling. Very good agreement was obtained between modeling and measurement for single element transducers. By coupling finite element analysis with the integral equation method using boundary elements, acoustic interaction effects were taken into account. Reasonable agreement was obtained between calculation and measurement for a 3 x 3 array.

Journal Article↗
PubMedDate not supplied

The effect of veneering materials on stress distribution in implant-supported fixed prosthetic restorations.

In this study, the effect of various materials used in fabricating superstructures for implant-retained fixed partial dentures on stress distribution around implant tissues was investigated. Five different mathematical models consisting of 11,361 nodes and 54,598 elements were constructed to study porcelain, gold alloy, composite resin, reinforced composite resin, and acrylic resin veneering materials using the 3-dimensional finite element analysis method. MARC K7.2/Mentat 3.2 software was used for the analysis. Reference points were determined on the cortical bone, where perpendicular, oblique, and horizontal forces were applied. Stress values created by oblique and horizontal forces appeared to be higher than those created by vertical forces. Stress seemed to be concentrated at the cortical bone around the cervical region of the implant. Gold alloy and porcelain produced the highest stress values in this region. Stresses created by acrylic resin and reinforced composite resin were 25% and 15% less, respectively, than porcelain or gold alloy. Porcelain and gold alloy produced stress values at the lingual implant sites that reached the ultimate strength values of the cortical bone.

Acrylic Resins↗
PubMed2004

[Effects of the directions of an extraoral retractive force on the displacement of and stress distribution in palate].

OBJECTIVE: The aim of this study was to assess the effects of varying retractive force directions on the displacement of and stress distributions in palate. METHODS: A three-dimensional finite element model of the nasomaxillary complex was created, consisting of 1638 isoparametric elements and 1827 nodes. An extraoral retractive force of 9.8N was applied to the upper canines in 3 different directions, i.e. parallel, 30 degrees upwards and downwards to the functional occlusal plane. Then we investigated the nature of stress distributions, the directions and amounts of displacement in palate by finite element analysis. RESULTS: In the midpalatal suture and transpalatal suture, all displacement directed to bone suture and increased gradually when the retractive force direction ranged from +30 degrees to -30 degrees. In the midmost part of palate, correlation between stress distributions and retractive force directions was not significant. Relatively compressive stresses were induced in the front and middle of the midpalatal suture, whereas nearly no stress was induced in the back. In the lateral part of palate, compressive stresses were nearly equal to tensile stresses in the front, while tensile stresses were induced in the middle and back. Meanwhile, there was no significant correlation between stress distributions and force directions. CONCLUSION: This study showed that the directions of retractive force had obvious effects on displacement but but little effect on stress distributions.

Biomechanical Phenomena↗
PubMed2006

Effect of loading method on the fracture mechanics of two layered all-ceramic restorative systems.

OBJECTIVE: The aim of this research was to evaluate both the fracture and impact strength of two core veneered all-ceramic systems and to reveal whether the speed of loading affects fracture mechanism. METHODS: The absorbed energy by (IPS)Empress-Eris crowns and Cercon-Ceram S crowns in a fracture strength test was compared by the energy absorbed in an impact strength test. The principles of fractography were used to identify fracture origin and dimensions and to calculate the stress at failure. Finite element analysis (FEA) was used to rationalize the results. RESULTS: For the (IPS)Empress 2-Eris crowns, there was a significant difference in the energy absorbed for the fracture test and the impact test, where for the Cercon-Ceram S, there was no significant difference. Despite the high strength of the zirconia cores there was no significant difference in the energy absorbed between the two systems in the impact strength test. The dominant mode of failure of layered all-ceramic restorations under occlusal loading is cone cracking in the veneering ceramic. SIGNIFICANCE: It was concluded that to exploit the high strength of the zirconia cores the strength of the veneering ceramic has to improve as delamination and cone cracking of the veneer are the most expected failure modes.

Analysis of Variance↗
PubMed2004

Stress-strain response in human dentine: rethinking fracture predilection in postcore restored teeth.

In this study, the biomechanical perspective of fracture predilection in post-core restored teeth is investigated using computational, experimental, and fractographic analyses. The computational finite element analysis and the experimental tensile testing are used to evaluate the stress-strain response in structural dentine. The fractographic evaluations are conducted using laser scanning confocal microscopy and scanning electron microscopy to examine the topography of dentine from experimentally fractured specimens, and clinically fractured post-core restored teeth specimens. These experiments aided in correlating the stress-strain response in structural dentine with cracks and catastrophic fractures in post-core restored teeth. It was observed from these experiments that the inner dentine displayed distinctly high strains (deformations), while the outer dentine demonstrated high stresses during tensile loading. This implies that the energy fed into the material as it is extended will be spread throughout the inner dentine, and there is less possibility of local increase in stress at the outer dentine, which can lead to the failure of dentine structure. During post-endodontic restoration with increase in loss of inner dentine, the fracture resistance factor contributed by the inner dentine is compromised, and this in turn predisposes the tooth to catastrophic fracture.

Adult↗
PubMedDate not supplied

Strength, reliability, and mode of fracture of bilayered porcelain/core ceramics.

PURPOSE: The aim of this investigation was to compare the biaxial flexural strength, its reliability, and the mode of fracture of bilayered disks made of two core materials (In-Ceram Alumina and In-Ceram Zirconia), both veneered with conventional feldspathic porcelain (Vita Alpha). MATERIALS AND METHODS: One hundred forty specimens (monolithic and bilayered) of In-Ceram Alumina, In-Ceram Zirconia, and Vita Alpha were made and tested with the biaxial flexural test. Finite element analysis was used to estimate the maximum tensile stress at fracture. Data were analyzed with one-way ANOVA, Tukey HSD, and Weibull distribution. SEM was used to identify the initial crack and characterize the fracture mode. RESULTS: All specimens with the core material on the bottom surface were statistically significantly stronger and more reliable than those with the porcelain on the bottom surface. Among them, In-Ceram Zirconia was stronger than In-Ceram Alumina. There was no statistically significant difference among groups when the porcelain underwent tension. Two different modes of fracture were observed in the bilayered samples according to which material was on the bottom surface. CONCLUSION: The material that underwent tensile stress dictated the strength, reliability, and fracture mode of the specimens. The design of the restorations and the actual distribution of the tensile stresses must be taken into account; otherwise, the significant contribution of stronger and tougher core materials to the performance of all-ceramic restorations may be offset by the weaker veneering porcelain.

Analysis of Variance↗
PubMed1997

Relationship between bone-prosthesis bonding and load transfer in total hip reconstruction.

The effect of bone-prosthesis bonding on proximal load transfer is investigated using a coupled experimental and finite element analysis on a synthetic femur. Three-dimensional finite element models for an intact femur and a femur implanted with a cementless prosthesis were constructed from the experimental models used, and the proximal femoral strains recorded for two loading conditions approximating a one-legged stance. The approach was used to investigate a press-fitted and a fully bonded bone-prosthesis structure to identify the stem-bone behaviour for both interface conditions and their implications for proximal bone load transfer. Regression slopes close to unity indicated that the finite element predictions were an accurate estimate of the experimental measurements. Physiological surface strains were recorded only when the abductor force was included in the loading. Meanwhile, experimental measurements and numerical predictions showed that a different load transfer pattern is to be expected for normally press-fitted and glued press-fitted stems. The finite element model for the treated femur, modelling both interface conditions correlated very well with the experimental model. These finite element models subsequently modified and used to analyse the effect of different interface conditions predicted a significant increase in the load transfer to the proximal calcar bone when only proximal bonding is achieved. This study suggests that information obtained for the assessment and prediction of total hip arthroplasty longevity by numerical and experimental techniques used together and in parallel is of greater value than either technique used alone. The employment of a femur analogue as featured in this study is also shown to be a suitable alternative to cadaveric specimens in such an analysis.

Biomechanical Phenomena↗
PubMed2001

Stress analysis of threaded cups.

Using finite element analysis we have studied the pelvic bony socket and compared it with radiological imaging using threaded acetabular cups of three different shapes (parabolic, conical, hemispherical). The two-dimensional model depicted a planar section through a left pelvic hemisphere. In all three cups the stress in the bony socket increased from lateral towards medial. Compressive stress was found on the superior and inferior parts of the cup, but mainly on the superior aspect, seen radiologically as new trabecular bone formation. The maximum compressive stresses were seen in the cranial curvature of the conical cup, with less in the parabolic form and least in the hemispheric form. The tensile stress at the bottom of the socket increased from the hemispheric to the conical shape. Radiological rarefaction gave an indication of lower stress. There was lower compressive stress between the teeth of the threads. This FE model uses computer simulation to predict bony changes with different designs of implant. The ability to simulate biological conditions is a valuable addition to the testing of mechanical strength.

Hip Joint↗
PubMed2006

New imaging technologies in the diagnosis of osteoporosis.

In the context of osteoporosis, bone quality--which encompasses trabecular and cortical micro-architecture, mass, and tissue mechanical & compositional properties--plays an important and as yet undiscovered role. Non-invasive assessment of bone quality has recently received considerable attention, as bone density alone has not been able to predict existing or future osteoporotic fractures, or to explain therapeutic effects of emerging treatments. The goal of this review, therefore, is to present imaging modalities and related analysis methods capable of assessing bone quality for improved diagnosis and care of osteoporotic individuals. The techniques described include quantitative ultrasound, quantitative computed tomography, peripheral quantitative tomography, micro computed tomography, magnetic resonance, radiographic texture analysis, as well as finite element analysis based on the above-mentioned imaging modalities. The performance of these techniques in predicting osteoporotic fracture and assessing strength indices are discussed.

Absorptiometry, Photon↗