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PubMedDate not supplied

Finite element analysis of deflections in major connectors for maxillary RPDs.

PURPOSE: The effect of major connector design on deflection in maxillary removable partial denture (RPD) frameworks under simulated occlusal loading was analyzed by means of three-dimensional finite element models. MATERIALS AND METHODS: Thirteen maxillary major connectors were produced for a Kennedy Class II case. Eleven frameworks consisted of posterior palatal straps with different anteroposterior widths at the midline. Anteroposterior and horseshoe bars were also constructed for comparison. In each framework, the occlusal rest on the abutment adjacent to the edentulous ridge was fixed in a vertical direction, and the rest on the contralateral side was fixed in all directions. A biting force of 20 N was vertically distributed simultaneously on each of the three missing posterior teeth locations. RESULTS: For the posterior palatal straps, the maximum vertical displacement at the saddle and the buccal displacement at both the saddle and the rest adjacent to the saddle decreased as their connector width increased from 6 to 29 mm, whereas maximum distal displacements were insensitive to the connector width. The posterior straps with anteroposterior widths of more than 18 mm revealed comparable rigidity to the anteroposterior bar. The horseshoe bar and the posterior straps with smaller widths demonstrated greater displacements than the other frameworks. CONCLUSION: The rigid connectors proved to be the most effective in transmitting applied occlusal forces to the contralateral side of the framework.

Bite Force↗

PubMed1994

The influence of geometry on the stress distribution in joints--a finite element analysis.

The incongruity of human joints is a phenomenon which has long been recognized, and recent CT-osteoabsorptiometric findings suggest that this incongruity influences the distribution of stress in joints during their normal physiological use. The finite element method (FEM) was therefore applied to five different geometric configurations consistent with the anatomy of articular surfaces, and a program with variable contact areas (Marc) was used to calculate the stress distribution for loads of 100 to 6,900 N. The assumption of congruity between head and socket results in a "bell-shaped" distribution of stress with a maximum value of 61.5 N/mm2 in the depths of the socket, decreasing towards zero at its edges. In the model with a flatter socket the von Mises stresses are higher (max. 101.3 N/mm2); with a deeper socket, lower (max. 53.0 N/mm2). If the diameter of the head is greater, the stresses build up from the periphery of the socket and move towards its depths as the load increases. The combination of an oversized head and a deeper socket results in the most satisfactory stress distribution (max. 43.2 N/mm2). These results extend previous photoelastic findings with incongruous joint surfaces. The calculated mechanical conditions show a relationship to the location of osteoarthritic changes, and are reflected by the distribution pattern of subchondral bone density. A more satisfactory stress distribution is found with functionally advantageous, incongruous joint surfaces (oversized head and deepened socket) than in the congruous joint, and a better nutritive situation for the articular cartilage seems likely.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorptiometry, Photon↗

PubMed1982

A non-linear finite element analysis of some early collapse processes in femoral head osteonecrosis.

Some aspects of the early collapse biomechanics of the segmentally necrotic adult human femoral head were studied, using a small-deformation plane strain, elasto-plastic finite element model. The computational procedure used was based upon the initial stress technique, and permitted study of stress and strain fields and of the progression of failure regions as a function of incrementally applied joint loads. The results consistently demonstrated both subchondral and deep cancellous failure patterns similar to those seen clinically. There was a clear distinction, however, between these two failure regimes, dependent primarily upon the relative strength deficits input for the subchondral versus the deep cancellous regions. Usually, the failure zone was appreciable only at significantly supra-physiological loads, reflecting the likely importance of fatigue events in the clinical collapse process. Although subchondral failure was always limited to the entire base region of the infarction wedge, the zones of deep failure varied considerably with changes in lesion geometry, usually being concentrated within the infarct near the underlying necrotic/viable interface.

Elasticity↗

PubMed1995

A 3-D finite element analysis of the natural frequencies of vibration of a stapes prosthesis replacement reconstruction of the middle ear.

In this work, the natural frequencies of vibration of two different stapes prosthesis replacement reconstructions have been analysed using the finite element method. Prosthesis 1 was constructed of fine stainless steel wire and a Teflon base, while prosthesis 2 was made entirely of Teflon. The results have indicated that generally, the first natural frequency of vibration falls as the prostheses become larger and more bulky. However, the fall in the first natural for prosthesis 1 was modest when compared with that of the isolated tympanic membrane. An important variable influencing frequencies and mode of vibration of the reconstruction was the tightness of fit of the prostheses within the remaining ossicular chain. The tightness of fit in this work was modelled as a range of spring constants applied at the stapes pseudo footplate, together with a series of joint elements at the incus tip/prosthesis head for the Teflon implant. When these spring constraints were below approximately 10 N/mm, the reconstruction exhibited normal mode 1 vibration behaviour, but at larger spring values, an abnormal mode 1 became established resembling the normal mode 2 vibration characteristics. The formation of new geometries and surfaces following reconstruction, introduces new constraints between umbo and stapes footplate particularly at the natural/artificial interfaces. These unnatural constraints may inhibit and modify the natural movements normally occurring at the stapes footplate leading to abnormal modes of vibration.

Ear Ossicles↗

PubMed2000

Head injury in facial impact--a finite element analysis of helmet chin bar performance.

The chin bar of a motorcycle helmet protects the rider from facial and head injuries. To evaluate the protective performance of chin bars against head injuries from facial impacts, an explicit finite element method was used to simulate the Snell Memorial Foundation test and a proposed drop test. The maximum acceleration and Head Injury Criterion (HIC) were employed to assess the impact-absorbing capability of the chin bar. The results showed that the proposed approach should be more practical than the Snell test, and provided more information for improving the chin bar design to protect against head injuries. The shell stiffness was important in determining the protective ability of the chin bar, but a chin bar with only an outer shell and comfort foam offered inadequate protection. An energy-absorbing liner was essential to increase the protective performance of the chin bar and the liner density should be denser than that used in the cranial portion of the helmet. For the chin bar with energy-absorbing liner, a shell design that is less stiff would provide better protection.

Craniocerebral Trauma↗

PubMed1992

Finite-element analysis in cartilage biomechanics.

Articular cartilage is a complex composite material in engineering terms. It is inhomogeneous, anisotropic and demonstrates a time-dependent nonlinear relationship between stress and strain. This paper reviews the application of the finite-element method to the loading of articular cartilage, and highlights the potential of this numerical technique in the investigation of osteoarthritis.

Biomechanical Phenomena↗

PubMed1995

Critique of conceptual basis of diffusing capacity estimates: a finite element analysis.

We present a simple geometric model of a pulmonary capillary segment containing a variable number of red blood cells. The pattern of CO transfer from alveolar air to capillary red blood cells in this model is accurately computed by a finite element method and used to explore conceptual flaws in the Roughton-Forster (RF) and morphometric methods of estimating pulmonary diffusing capacity for CO. The CO uptakes calculated by the finite element method at two alveolar O2 tensions are introduced into the RF model to determine whether the anatomically defined membrane component of diffusing capacity for CO (DmCO) and pulmonary capillary blood volume (Vc) are recovered. The same capillary model is also subjected to standard morphometric analysis. Results are compared at different levels of capillary hematocrit (Hct). The RF method accurately recovers DmCO and Vc at a low Hct but modestly overestimates DmCO and underestimates Vc at higher Hct; errors arise because conductance of the tissue-plasma membrane for CO varies with alveolar O2 tension. The morphometric method seriously overestimates DmCO because the true tissue-plasma resistance to diffusion is underestimated and the effective membrane utilized for diffusion is overestimated; these errors are accentuated by a low Hct.

Animals↗

PubMed2006

Prediction of torsional failure in 22 cadaver femora with and without simulated subtrochanteric metastatic defects: a CT scan-based finite element analysis.

BACKGROUND: In metastatic bone disease, prophylactic fixation of impending long bone fracture is preferred over surgical treatment of a manifest fracture. There are no reliable guidelines for prediction of pathological fracture risk, however. We aimed to determine whether finite element (FE) models constructed from quantitative CT scans could be used for predicting pathological fracture load and location in a cadaver model of metastatic bone disease. MATERIAL AND METHODS: Subject-specific FE models were constructed from quantitative CT scans of 11 pairs of human femora. To simulate a metastatic defect, a transcortical hole was made in the subtrochanteric region in one femur of each pair. All femora were experimentally loaded in torsion until fracture. FE simulations of the experimental set-up were performed and torsional stiffness and strain energy density (SED) distribution were determined. RESULTS: In 15 of the 22 cases, locations of maximal SED fitted with the actual fracture locations. The calculated torsional stiffness of the entire femur combined with a criterion based on the local SED distribution in the FE model predicted 82% of the variance of the experimental torsional failure load. INTERPRETATION: In the future, CT scan-based FE analysis may provide a useful tool for identification of impending pathological fractures requiring prophylactic stabilization.

Aged↗

PubMed1994

[Three dimensional finite element analysis of stress induced by orthodontic forces in the periodontal tissue].

The purpose of this study was to investigate the stress induced in the periodontal tissue of the upper central incisor by application of orthodontic forces. A three dimensional finite element model consist of tooth, periodontal ligament (PDL), cancellous and compact bone was established and the following results were obtained: (1) The highest stresses were observed on the root surface, the intermediate on the alveolar bone and the lowest in the PDL. (2) Stress condition on the surface of root and alveolar bone is very complex. The maximum, intermediate and minimum principle stresses on the same area are quite different, but the three principal stresses in the PDL are similar. (3) Regarding to tipping and torque movement, the stress value varied largely from the cervix to the apex, and there is stress concentration at the cervix and the apex. For bodily movement when M/F is -10.30, the stress induced is homogeneous and the difference of the stress values from the cervix to the apex is little, which seems to be more physiological.

Alveolar Process↗

PubMed1996

Finite element analysis of temperature controlled coagulation in laser irradiated tissue.

The Theoretical study of thermal damage processes in laser irradiated tissue provides further insight into the design of optimal coagulation procedures. Controlled laser coagulation of tissue was studied theoretically using a finite element method with a modulating laser heat source to simulate feedback controlled laser delivery with a constant surface temperature. The effects of uncertainty in scattering and absorption properties of the tissue, thermal denaturation induced changes in optical properties, and surface convection were analyzed. Compared to a single pulse CW irradiation in which a doctor would presumably stop CW laser delivery after noticing some effect such as vaporization or carbonization, the constant surface temperature scenario provided a better overall control over the coagulation process. In particular, prediction of coagulative damage in a constant temperature scenario was less sensitive to uncertainties in optical properties and their dynamic changes during the course of coagulation. Also, subsurface overheating under surface convective conditions could be compensated for under constant temperature irradiation by lowering the surface temperature.

Animals↗

PubMed1987

Mathematical and finite element analysis of spine injuries.

A critical review of the anatomical, physiological, epidemiological, and biomechanical aspects of spine injuries are presented. These are discussed in light of the mechanical load that produces the trauma. Emphasis is given to the mathematical and finite element modeling aspects of spinal injury that focuses on the tolerance criteria. In the area of spinal mechanics, static and dynamic models are reviewed. Included are the continuum and discrete parameter models of the intact spine and finite element models of its components. A section on the role of constituent law in the assessment of trauma to the spine is given. Finally, a discussion follows on the future research in this domain.

Humans↗

PubMed1998

Finite element analysis of the lower lumbar neural arch under facet loading.

To evaluate the mechanical effect of the direction of facet load on the isthmus stresses of the lower lumbar neural arch, stress analyses were performed by using three-dimensional finite element models of isolated L4 and L5 vertebrae with particular emphasis on accurate discretization of the posterior elements. The bilateral symmetric or unilateral facet loads, with a constant magnitude, were applied within the sagittal and transverse planes. The largest maximal principal stress in the neural arch (the largest sigma(max)) tended to be qualitatively similar in L4 and L5. At the physiologic range, the largest sigma(max), observed on the anterior surface of the isthmus, was relatively insensitive to the sagittal plane loadings but sensitive to the transverse plane loadings. The values of the largest sigma(max) of L4 and L5 were low at the more frontally directed facet load. The magnitude and direction of the largest sigma(max) depended upon the facet loadings mainly on the ipsilateral side and partly on the opposite side. The results suggest that the direction of facet load, which may be characterized by the facet orientation, can have mechanical effects on the occurrence and direction of isthmic crack.

Computer Simulation↗

PubMed1995

Finite element analysis in the design and characterization of an absorbable cement restrictor.

The benefit of using a cement restrictor to achieve cement pressurization during total hip arthroplasty is well established. An absorbable cement restrictor design has been developed with the use of a finite element model. The non-linear axisymmetric model was used to optimize specific parameters so as to perform within acceptable limits when tested over a specified range of medullary canal sizes. The results achieved from a hybrid experimental/analytical design methodology allowed for a shorter development cycle for the initial size and each additional size in the design family thereafter. The resulting cement restrictor design was compared to and exceeded the performance of currently clinically accepted devices in resisting migration.

Biomechanical Phenomena↗

PubMed2004

Continuum diffusion reaction rate calculations of wild-type and mutant mouse acetylcholinesterase: adaptive finite element analysis.

As described previously, continuum models, such as the Smoluchowski equation, offer a scalable framework for studying diffusion in biomolecular systems. This work presents new developments in the efficient solution of the continuum diffusion equation. Specifically, we present methods for adaptively refining finite element solutions of the Smoluchowski equation based on a posteriori error estimates. We also describe new, molecular-surface-based models, for diffusional reaction boundary criteria and compare results obtained from these models with the traditional spherical criteria. The new methods are validated by comparison of the calculated reaction rates with experimental values for wild-type and mutant forms of mouse acetylcholinesterase. The results show good agreement with experiment and help to define optimal reactive boundary conditions.

Acetylcholinesterase↗

PubMedDate not supplied

Finite element analysis of a new system (IL) for supporting an implant-retained cantilever prosthesis.

A new system (the IL system) for supporting the distal extension of a cantilevered prosthesis is designed from a short implant and a special ball-type attachment. The finite element method was employed to analyze this system and the surrounding bone, as well as a conventional prosthesis, in two dimensions. Effective and maximum stresses in tension and compression were determined. A comparison of these quantities between the IL-supported prosthesis and a conventional prosthesis was carried out. It was observed that use of this system to support the distal extension of a cantilevered prosthesis dramatically lowers the stresses in the bone, cantilever, and implants. Therefore, this system may reduce failures within the implants, prostheses, and surrounding bone. Moreover, employment of a relatively long-span prosthetic extension in the posterior region of the jaw should be possible. This new system is recommended for completely and partially edentulous patients.

Dental Implants↗

PubMedDate not supplied

[Mechanical stress on the osseous tibial plateau in complement joint surface replacement--a finite element analysis].

For an unconstrained bicondylar sledge knee prosthesis the mechanical load of the bony support is crucial. For a design of a tibial component of such a prosthesis with improved anatomical features allowing a complete cortical support of the rim of the prosthesis, a finite element study was performed. Stress reactions of the bone for different implantation modes were calculated. Irrespective of the bony support of the prosthesis, tensile stresses are always transferred at the interface prosthesis/bone into the bone. For a complete cortical support of the rim of prosthesis, the areas of tensile stress in the bone are closely related to areas of high compression stress. If there is cortical support of the prosthesis only on the medial side due to an undersized prosthesis, this is only of minor influence on the stress pattern in the bone. However, if there is cortical support of the prosthesis only on the lateral side, there are large areas of tensile stresses in the lateral compartment of the tibial plateau. However, tensile stress transfer in the tibial plateau must be regarded as unphysiologic and therefore unfavourable. Therefore, if intraoperatively complete cortical support of the prosthesis cannot be achieved a more medial cortical support of such a prosthesis should be preferred to a lateral cortical support.

Biomechanical Phenomena↗

PubMed1995

Finite element analysis of nonlinear pulsatile suspension flow dynamics in blood vessels with aneurysm.

A nonlinear pulsatile suspension flow in a dilated vessel is numerically analysed. Two sets of highly coupled nonlinear partial differential equations governing the suspension flow are numerically solved, to simulate the suspension flow dynamics. A transient velocity-pressure (UVP) finite element method (FEM) and a stable time integration scheme, based on a predictor-corrector strategy, with constant error monitoring are employed in the flow analysis. The pulsatile suspension flow is characterized by analysing the flow, pressure and stress fields. Effects of the nonlinear particulate phase on the nonlinear suspending fluid phase are brought out by comparing the suspension flow results with those of homogeneous flow. Particles are seen to dampen the flow velocity, wall and central axis pressure, pressure gradient and wall shear stress. time-dependent recirculation regions which are sensitive to the presence of particles are seen in the dilated portion of the vessel. These recirculation regions favour thrombogenesis. The nonlinear effects due to the vessel geometry and those due to the convective terms dominate the dampening effect of the particles. These nonlinear effects are depicted through the transverse velocity and pressure plots. Wall shear stresses of suspension flow are not only high but also alternate in direction.

Algorithms↗

PubMed1997

Finite element analysis of human knee joint in varus-valgus.

OBJECTIVE: The overall response, load transmission, role of ligaments, and state of stress in various components under varus-valgus moments in the intact and collateral-deficient tibiofemoral joint are investigated. DESIGN: A non-linear finite element model consisting of bony structures (tibia and femur), their articular cartilage layers, medial and lateral menisci and four primary ligaments (cruciates and collaterals) is utilized. BACKGROUND: Valgus and varus stresses are among the primary mechanisms of injury to knee ligaments. Several in vitro studies have investigated the role of ligaments in resisting such loads and on the way deficiency in either collateral may affect the response. METHODS: Cartilage layers are isotropic while menisci are non-homogeneous composite. The articulation of cartilage layers with each other and with the intervening menisci and the wrapping of the medial collateral ligament around the tibial edge are treated as large displacement frictionless contact problems. The non-linear elastostatic response of the joint at full extension is computed under varus-valgus moments applied to the femur with the tibia fixed. Cases simulating deficiency in collaterals and constraint on femoral axial rotation are also studied. RESULTS: The response is non-linear with large coupled axial rotations, internal in varus and external in valgus. In intact and collateral-deficient states, the joint shows varus or valgus openings so that the articulation occurs at one plateau only, medial in varus and lateral in valgus. Large tensile forces in cruciates in collateral-cut models generate higher compression penalty on the loaded plateau. CONCLUSIONS: Collaterals are the primary load-bearing structures; their absence would substantially increase primary laxities, coupled axial rotations, forces in cruciates, and articular contact forces. Good agreement with measurements is found. RELEVANCE: Detailed knowledge of joint biomechanics is essential in the diagnosis, prevention and treatment of observed disorders. Absence of collateral ligaments increases the loads in cruciates and contact stresses transmitted through cartilage layers and menisci, and thus places the affected components at more risk, especially when varus-valgus is accompanied by other modes of loading as well.

Journal Article↗