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PubMedDate not supplied

Physical signals and solute transport in human intervertebral disc during compressive stress relaxation: 3D finite element analysis.

A 3D finite element model for charged hydrated soft tissues containing charged/uncharged solutes was developed based on the multi-phasic mechano-electrochemical mixture theory (Lai et al., J. Biomech. Eng. 113 (1991), 245-258; Gu et al., J. Biomech. Eng. 120 (1998), 169-180). This model was applied to analyze the mechanical, chemical and electrical signals within the human intervertebral disc during an unconfined compressive stress relaxation test. The effects of tissue composition [e.g., water content and fixed charge density (FCD)] on the physical signals and the transport rate of fluid, ions and nutrients were investigated. The numerical simulation showed that, during disc compression, the fluid pressurization was more pronounced at the center (nucleus) region of the disc while the effective (von Mises) stress was higher at the outer (annulus) region. Parametric analyses revealed that the decrease in initial tissue water content (0.7-0.8) increased the peak stress and relaxation time due to the reduction of permeability, causing greater fluid pressurization effect. The electrical signals within the disc were more sensitive to FCD than tissue porosity, and mechanical loading affected the large solute (e.g., growth factor) transport significantly, but not for small solute (e.g., glucose). Moreover, this study confirmed that the interstitial fluid pressurization plays an important role in the load support mechanism of IVD by sharing more than 40% of the total load during disc compression. This study is important for understanding disc biomechanics, disc nutrition and disc mechanobiology.

Biological Transport↗
PubMed1999

Design optimization and evolution of bonded ceramics for the anterior dentition: a finite-element analysis.

OBJECTIVE: Finite-element method was used to explore the stress distribution of incisors restored with porcelain veneers. The design of the incisal palatal finish line was analyzed as a function of incisal overlap and initial tooth substance loss (coronal fractures). METHOD AND MATERIALS: The treatment of intact and fractured incisors was investigated using 8 different designs of porcelain veneer. The palatal finish line varied from butt margins to extended chamfers. The stress distribution was assessed in a 2-dimensional finite-element model, reproducing a buccolingual cross section of an incisor. A palatal 50-N horizontal force was applied to the incisal edge to simulate an extreme functional load. The palatal surface tangential stresses were calculated. RESULTS: Considerable differences were detected in the stresses at the level of the incisal-palatal restoration margin. The margins of restorations with limited incisal overlap (butt margin or minichamfer) showed low tensile stresses or even compressive stresses. Restorations with a long chamfer extending into the palatal concavity were subjected to the highest tensile stresses. In the presence of moderate crown fractures (incisal one third) or severe wear, butt margins limited the palatal extension of ceramic, thus reducing the amount of stress at the restoration interface. In the presence of severe crown fractures (incisal two thirds), the margins (either butt or chamfered) were subjected to low tensile forces when located in the smooth convex area of the cingulum. CONCLUSION: Because of the geometry and natural elastic modulus of mineralized tooth structures, a concentration of tensile stresses is formed at the palatal concavity of teeth restored with porcelain veneers. Long chamfers extending into the palatal concavity are unfavorable because thin extensions of ceramic are generated in an area of maximum tensile stresses. Minichamfers or butt margins are generally recommended, especially in the presence of moderate crown fractures or severe wear.

Compressive Strength↗
PubMed2006

[A biomechanical study of the mechanical stress transmission of dental implants using finite element analysis. Review of literature. Part I].

Finite Element Analysis (FEA) is a computerised investigative method that is capable of determining the mechanical stress arising in various objects and their environment as a result of forces effecting the system by using a mathematical model. The method is most often used for purposes of technical, engineering design, but is very useful for medical purposes-the static and functional investigation of the skeletal and motor system of the human body-as well. The transmission of mechanical stress between the implant and bone depends on a number of factors, and its description is quite complicated. A model has to be created to perform a FEA, the geometric data of the implant, the mechanical properties of the bone and the parameters of the bone-implant interface have to be determined, a so-called finite element network has to be created. Valuable data can be obtained by changing the individual elements of the system. The study of dental implants makes it possible to better investigate biomechanical conditions and thus the further perfection of implant methods. In the first part of the present two-part publication authors review the possibilities of use of the finite element analysis in examining the stress transmission of dental implants. In the second part of the publication their own studies will be presented.

Biomechanical Phenomena↗
PubMed2001

Bone loading pattern around implants in average and atrophic edentulous maxillae: a finite-element analysis.

Introduction: Oral implants placed in the maxilla, especially the posterior region, have a lower success rate than those placed in the mandible. Poor bone quantity and quality have been suggested as a reason for this differential success rate. Objective: The purpose of this study was, therefore, to evaluate stress and strain distributions around loaded implants in the normal and atrophic maxilla by finite-element (FE) analyses. Material: FE models of a solitary implant were generated to determine stresses and strains in the bone adjacent to the implant surface under loading conditions. Study design: Different bony situations and implant lengths were used in a FE model. Static loads were applied axially and the resulting stresses and strains calculated. Results: Bone quality and quantity play a major role in decreasing bone strains adjacent to the implant surface under loading. It was found that stresses were more homogeneously distributed when more spongy bone was present. Decreased bone height was found to have less pronounced effects on strain and stress alterations than poor bone quality. Atrophic bony dimensions in combination with poor bone quality were associated with surface strains exceeding physiological levels (>6000 microstrains). Conclusion: Our investigation indicates that supraphysiological bone strains adjacent to the implant surface should be expected under mechanical loading in the atrophic maxilla. Copyright 2001 European Association for Cranio-Maxillofacial Surgery.

Journal Article↗
PubMedDate not supplied

Influence of prosthesis material on stress distribution in bone and implant: a 3-dimensional finite element analysis.

A 3-dimensional finite element analysis was conducted to assess stress distribution in bone, implant, and abutment when gold alloy, porcelain, or resin (acrylic or composite) was used for a 3-unit prosthesis. A unit force was applied axially and then buccolingually to the center of the pontic. For gold and porcelain, similar maximum equivalent stress was found in each part of the models. In almost all cases, stress in the model with the resin prostheses was similar to or higher than that in the models with the other 2 prosthesis materials. The highest increase in stress with the resins was found in the implant-abutment unit under axial load. The protective role of resin for the implant-bone interface could not be demonstrated under the conditions of this analysis.

Acrylic Resins↗
PubMed1994

Finite element analysis of cerebral contusion.

Finite element analysis was carried out to study the mechanism of cerebral contusion. Clinical findings indicate that most cerebral contusions in the absence of skull fracture occur at the frontal and temporal lobes. To explain these observations, cavitation and shear strain theories have long been advocated. Plane strain finite element models of a parasagittal section of the human head were developed in the present study. The model was first validated against a set of experimental results from the literature. Frontal and occipital impacts were then simulated, and pressure and shear stress distributions in the brain were compared. While comparable negative pressures always developed in the contrecoup regions, shear stress distributions remained nearly identical regardless of the impact direction, consistent with the clinically observed pattern for contusion. Therefore, shear strain theory appears to account better for the clinical findings in cerebral contusion.

Acceleration↗
PubMed1987

Comparative study of normal, Crouzon, and Apert craniofacial morphology using finite element scaling analysis.

Finite element scaling analysis is used to study differences in morphology between the craniofacial complex of normal individuals and those affected with the syndromes of Apert and Crouzon. Finite element scaling quantifies the differences in shape and size between forms without reference to any fixed, arbitrary registration point or orientation line and measures the amount of form change required to deform one object into another. Two-dimensional coordinates of landmarks digitized from annual sets of cephalometric radiographs were used in the analysis. A simple tabulation shows no difference in variances between the normal and pathological samples. A test of mean differences depicts the Apert and Crouzon morphologies as significantly different from normal. The Apert palate differs from normal in shape in the older age groups analyzed, and palatal size differences are most common at the posterior nasal spine. The Apert pituitary fossa and basi-occiput are significantly larger than normal. The Crouzon pituitary fossa is also larger than normal, but the difference is not always significant. The typical morphology of the Crouzon nose is due more to differences in shape than size. The Crouzon basi-occiput is significantly smaller than normal. An age association of the differences between the normal and pathological craniofacies was found in Apert syndrome but not in Crouzon syndrome. Apert syndrome is characterized by a more homogeneous pattern of craniofacial dysmorphology from 6 months to 18 years of age than Crouzon syndrome.

Acrocephalosyndactylia↗
PubMed1983

Pre-collapse stress redistributions in femoral head osteonecrosis--a three-dimensional finite element analysis.

Three-dimensional finite element analysis is used to explore the influence of several lesion characteristics upon mechanical stress distributions in segmentally necrotic human femoral heads. Variables studied parametrically included apparent modulus deficits within the lesion proper, as well as the depth, width, and location of the infarcted head regions. The detailed patterns of stress redistribution were complex and were found to be a strong function of the specific lesion characteristics. The salient phenomenon, however, was one of preferential load uptake by the stiffer bone surrounding the lesion. Since computed stress reductions within the infarctions were usually much smaller than experimentally observed strength reductions, the data suggest a strong tendency for an elevated incidence of trabecular fatigue fractures in the affected regions.

Adult↗
PubMed2005

[Simulation of airbag impact on eyes after trabeculectomy by finite element analysis method].

PURPOSE: A finite element computer model of the human eye after trabeculectomy was used in an experiment of simulated airbag ocular injury. METHODS: A half-layer-incised scleral flap was created on the limbus and the strength of its adhesion to the outer sclera was set at 30%, 50% and 100%. The simulations were performed at a workstation using the finite element analysis program PAM CRASH (Nihon ESI, Tokyo, Japan), and the airbag was set to hit the surface of the post-trabeculectomy eye at various velocities in two directions, straight to the corneal center or straight to the scleral flap. RESULTS: In the case of airbag impact on the corneal center, the scleral flap was unlikely to rupture except when the airbag impact velocity was 40 m/sec. In the case of airbag impact on the scleral flap, at the lowest impact velocity of 20 m/sec, partial scleral flap rupture was likely to occur only at the lower adhesion strength, and scleral laceration extending to the posterior sclera was observed at impact velocities of over 30 m/sec. CONCLUSIONS: These simulation results suggest that current airbags may induce globe rupture in eyes after trabeculectomy treatment.

Air Bags↗
PubMed2005

Estimation of Young's modulus and Poisson's ratio of soft tissue from indentation using two different-sized indentors: finite element analysis of the finite deformation effect.

Young's modulus and Poisson's ratio of a tissue can be simultaneously obtained using two indentation tests with two different sized indentors in two indentations. Owing to the assumption of infinitesimal deformation of the indentation, the finite deformation effect of indentation on the calculated material parameters was not fully understood in the double indentation approach. However, indentation tests with infinitesimal deformation are not practical for the measurement of real tissues. Accordingly, finite element models were developed to simulate the indentation with different indentor diameters and different deformation ratios to investigate the finite deformation effect of indentation. The results indicated that Young's modulus E increased with the increase in the indentation deformation w, if the finite deformation effect of indentation was not considered. This phenomenon became obvious when Poisson's ratio v approached 0.5 and/or the ratio of indentor radius and tissue thickness a/h increased. The calculated Young's modulus could be different by 23% at 10% deformation in comparison with its real value. The results also demonstrated that the finite deformation effect to indentation on the calculation of Poisson's ratio v was much smaller. After the finite deformation effect of indentation was considered, the error of the calculated Young's modulus could be controlled within 5% (a/h = 1) and 2% (a/h = 2) for deformation up to 10%.

Connective Tissue↗
PubMed2007

Tissue strain amplification at the osteocyte lacuna: a microstructural finite element analysis.

A parametric finite element model of an osteocyte lacuna was developed to predict the microstructural response of the lacuna to imposed macroscopic strains. The model is composed of an osteocyte lacuna, a region of perilacunar tissue, canaliculi, and the surrounding bone tissue. A total of 45 different simulations were modeled with varying canalicular diameters, perilacunar tissue material moduli, and perilacunar tissue thicknesses. Maximum strain increased with a decrease in perilacunar tissue modulus and decreased with an increase in perilacunar tissue modulus, regardless of the thickness of the perilacunar region. An increase in the predicted maximum strain was observed with an increase in canalicular diameter from 0.362 to 0.421 microm. In response to the macroscopic application of strain, canalicular diameters increased 0.8% to over 1.0% depending on the perilacunar tissue modulus. Strain magnification factors of over 3 were predicted. However, varying the size of the perilacunar tissue region had no effect on the predicted perilacunar tissue strain. These results indicate that the application of average macroscopic strains similar to strain levels measured in vivo can result in significantly greater perilacunar tissue strains and canaliculi deformations. A decrease in the perilacunar tissue modulus amplifies the perilacunar tissue strain and canaliculi deformation while an increase in the local perilacunar tissue modulus attenuates this effect.

Adaptation, Physiological↗
PubMed2001

Replacing the nucleus pulposus of the intervertebral disk: prediction of suitable properties of a replacement material using finite element analysis.

An axisymmetric finite element model of a human lumbar disk was developed to investigate the properties required of an implant to replace the nucleus pulposus. In the intact disk, the nucleus was modeled as a fluid, and the annulus as an elastic solid. The Young's modulus of the annulus was determined empirically by matching model predictions to experimental results. The model was checked for sensitivity to the input parameter values and found to give reasonable behavior. The model predicted that removal of the nucleus would change the response of the annulus to compression. This prediction was consistent with experimental results, thus validating the model. Implants to fill the cavity produced by nucleus removal were modeled as elastic solids. The Poisson's ratio was fixed at 0.49, and the Young's modulus was varied from 0.5 to 100 MPa. Two sizes of implant were considered: full size (filling the cavity) and small size (smaller than the cavity). The model predicted that a full size implant would reverse the changes to annulus behavior, but a smaller implant would not. By comparing the stress distribution in the annulus, the ideal Young's modulus was predicted to be approximately 3 MPa. These predictions have implications for current nucleus implant designs.

Journal Article↗
PubMed1998

The simulation and calculation of the fatigue of the lower complete denture in function by means of the finite element analysis.

This paper presents a finite element analysis, by which the stress distribution during function of a lower jaw acrylic-resin complete denture can be shown. The geometry of a prosthesis has been approximated by measuring, its elementary dimensions, as well as the dimensions of the characteristic cross-sections, on an already completed denture. Based upon these dimensions a mesh, (a three-dimensional network diagram) of finite elements was made. The results obtained are presented both graphically and numerically. The equivalent fatigue stresses, according to von Mises' energetic theory of firmness, expressed in MPa (or in N/mm2), are also shown. The results obtained enable us to gain an insight into lower complete denture fatigue, and could also be used when optimizing the shape of a denture. Furthermore, they could indicate possible causes of the fatigue fractures of a denture, particularly in the area between the left and the right canines.

Acrylic Resins↗
PubMed2006

A comparison of 2D and 3D finite element analysis of a restored tooth.

The finite element method is widely used in dental research. The decision to use two-dimensional (2D) or three-dimensional (3D) modelling is dependent on many interrelated factors. The purpose of the present study was to compare and contrast 2D and 3D finite element analysis (FEA) in investigating the mechanical behaviour of a maxillary premolar restored with a full crown under similar conditions of axial and lateral occlusal loading. The 2D analysis required modelling both a buccolingual and mesiodistal section of the restored premolar and for comparison sections of a 3D model were examined. Differences in the results for displacement and maximum principal stress distribution within the component structures and interfaces of the 2D and 3D models were, in general, attributable to differences in geometry represented in the models. Maximum principal stresses tended to be greater under lateral rather than axial occlusal loading. It was concluded that 2D FEA may find application in investigating key aspects of the mechanical behaviour of a dental restoration in a single tooth unit, but that in certain situations combinations of 2D and 3D FEA may offer the best understanding of the biomechanical behaviour of complex dental structures. Sophisticated FE models are required to better understand the mechanical behaviour of restored tooth units.

Bicuspid↗
PubMed2003

Evaluation of trajectories and contact pressures for the straight nucleus cochlear implant electrode array - a two-dimensional application of finite element analysis.

A two-dimensional (2D) finite element analysis has been used in this study to model the insertion of the Nucleus electrode array with different stiffness properties in order to evaluate the propensity of damage by visualizing the predicted trajectories and by comparing the buckling stresses and the contact pressures at the tip (and its distribution along the length) of the electrode array. Previous temporal bone studies have shown that damage during insertion of an electrode array around the basal turn of the cochlear spiral could be related to the design and the stiffness properties of the electrode array. However, it is difficult to evaluate different designs of electrode arrays purely by experimental methods as the experimental conditions and their results are difficult to reproduce. Three electrode arrays with different mechanical properties, i.e. uniform stiffness, graded stiffness, and a soft tip have been modelled. Buckling stress and contact pressure at the tip of the electrode array were found to be highest for the arrays with uniform stiffness. The contact pressures at the tip of the electrode array appeared strongly influenced by the stiffness profile and were optimal for graded stiffness. The results indicate the importance of the electrode array design and stiffness properties in minimizing trauma. However, there are a number of limitations in the present 2D evaluation which will require further analysis using a three-dimensional model to obtain definitive results.

Cochlea↗
PubMed2006

Finite element analysis of a bone-implant system with the proximal femur nail.

Static analysis with finite element of a realistic femur nail bone-implant system in a typical proximal femoral fracture under physiological load bearing situations provides results for stress, displacement and strain. The question to be answered is, if simulation with the finite element analysis is able to explain biomechanically clinical observed patterns of failure. Surface-Reconstruction with CT database of a proximal femur and reconstruction with CT based density data was done. Next steps were to unite the bone structure with the Proximal Femoral Nail and to model two relevant fractures (31-A2.2 and A2.3 according AO). After modelling of geometry, isotropic material behaviour and load application numeric calculation of the femur-nail system with FE-software was performed. FE simulation mainly shows an axial dislocation of the femoral head screw with nearly no dislocation of the antirotation screw. This so-called z-effect therefore means: (1) Tilting of the proximal main fragment around the sagittal axis between the screws and (2) relative movement of both screws in the frontal plane. Relative movement of the two screws against each other could be the reason for implant failure, the so called cut out. Furthermore simulation shows different gliding of the screws explaining the so called z-telescoping. The analyzed stress patterns have to be relativized, because isotropic material behaviour of cancellous bone was assumed. Further examinations for this issue are necessary.

Biomechanical Phenomena↗
PubMed2004

Analysis of tablet compaction. II. Finite element analysis of density distributions in convex tablets.

A Drucker-Prager/cap constitutive model, where the elastic and plastic model parameters are expressed as a function of relative density (RD), was presented in a companion article together with experimental calibration procedures. Here, we examine the RD distribution in curved-faced tablets with special reference to the die wall lubrication conditions. The compaction of powders is examined using finite element analysis, which involves the following factors: constitutive behavior of powder, friction between powder and tooling, geometry of die and punches, sequence of punch motions, and initial conditions that result from die fill. The predictions of the model are validated using experimental RD maps. It is shown that different die wall lubrication conditions induce opposite density distribution trends in identical tablets (weight, height, and material). The importance of the internal tablet structure is illustrated with respect to break force, failure mode, and friability: it is demonstrated that for a given average tablet density the break force and failure mode are not unique. Also, tablet regions having lower density locally have higher propensity for damage. The applicability of finite element analysis for optimizations of formulation design, process development, tablet image, and tool design is discussed.

Chemistry, Pharmaceutical↗