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PubMed2002

Analysis of the shape of the tibial tray in total knee arthroplasty using a three dimension finite element model.

OBJECTIVE AND DESIGN: The purpose of this study was to evaluate whether the stress and displacement change with differing shapes of the tibial component in total knee arthroplasty. BACKGROUND: There are few reports on tibial tray mechanics with and without a posterior concave slot, using three-dimensional finite element analysis. METHODS: By considering two different shapes for the tibial component, we analyzed the von Mises stresses and displacements at the component/bone interface and surrounding bone using a three-dimensional finite element model. RESULTS: There was no difference between the two designs in regards to the von Mises stress fields or displacements. The displacement of the tibial tray with a posterior concave slot was less than that of the tray without one in some of the loading configurations. The posterior concave slot appears to reduce the micromotion of the tibial component. DISCUSSION AND CONCLUSION: Overall, this finite element analysis showed little difference between the two different types of tibial base plates used with both posterior cruciate ligament retention and substitution. The results of this finite element model analysis do not support the use of tibial base plates without a posterior cut-out slot.

Biomechanical Phenomena↗
PubMed1997

[Three-dimensional finite element stress analysis of magnetical retaining and bar retaining in overdenture implants].

The purpose of this study was to determine which type of denture retaining implants can produce better biomechanical effect on the bone tissue. Two mechanical models of magnetically retained complete overdenture supported by osseo-integrated implant and bar-retained complete over denture supported by osseo-integrated implant were made. The peak stress in mandibular peri-implant bone tissue of the models were studied under the same loading conditions vertically and horizontally by three-dimensional FEM stress analysis. The results were as follows: (1) Both types of dentures retention can produce significant stress effect on the peri-implant and other regions of the jaw bone and (2) Magnetical retention is more beneficial to maintenance both of peri-implant bone tissue and long-term success of denture supported by osseo-integrated implant than bar retention does.

Dental Implantation, Endosseous↗
PubMed2004

Mechanical analysis of atherosclerotic plaques based on optical coherence tomography.

Finite element analysis is a powerful tool for investigating the biomechanics of atherosclerosis and has thereby provided an improved understanding of acute myocardial infarction. Structural analysis of arterial walls is traditionally performed using geometry contours derived from histology. In this paper we demonstrate the first use of a new imaging technique, optical coherence tomography (OCT), as a basis for finite element analysis. There are two primary benefits of OCT relative to histology: 1) imaging is performed without excessive tissue handling, providing a more realistic geometry than histology and avoiding structural artifacts common to histologic processing, and 2) OCT imaging can be performed in vivo, making it possible to study disease progression and the effect of therapeutic treatments in animal models and living patients. Patterns of mechanical stress and strain distributions computed from finite element analysis based on OCT were compared with those from modeling based on "gold standard" histology. Our results indicate that vascular structure and composition determined by OCT provides an adequate basis for investigating the biomechanical factors relevant to atherosclerosis and acute myocardial infarction.

Coronary Artery Disease↗
PubMed2003

Evaluation of the mechanical characteristics of the implant-abutment complex of a reduced-diameter morse-taper implant. A nonlinear finite element stress analysis.

The purpose of this study was to evaluate the mechanical characteristics of the implant-abutment connection of a reduced-diameter ITI dental implant. A finite element model of a slashed circle 3.3 mm x 10 mm ITI solid-screw implant and a 6 degrees solid abutment 4 mm in height was constructed, and the implant-abutment complex was embedded vertically in the center of a slashed circle 1.5 cm x 1.5 cm acrylic cylinder. Static vertical and oblique loads of 300 N were applied in separate load cases. The contact area was defined between the implant-abutment connection and nonlinear finite element stress analysis was performed. The magnitude and distribution of Von Mises stresses and displacement characteristics were evaluated. In vertical loading, Von Mises stresses concentrated around the implant-abutment connection at the stem of the screw and around the implant collar. Oblique loading resulted in a 2-fold increase in stresses at the implant collar, which was close to the yield strength of titanium. Displacement values under both loading conditions were negligible. We conclude that, in a reduced-diameter ITI dental implant, vertical and oblique loads are resisted mainly by the implant-abutment joint at the screw level and by the implant collar. The neck of this implant is a potential zone for fracture when subjected to high bending forces. The reduced-diameter ITI dental implant might benefit from reinforcement of this region.

Biomechanical Phenomena↗
PubMed1996

Finite element stress analysis of three filling techniques for class V light-cured composite restorations.

An important disadvantage of current dental resin composites is polymerization shrinkage. This shrinkage has clinical repercussions such as sensitivity, marginal discoloration, and secondary caries. The objective of this study was to compare three filling techniques in terms of the transient stresses induced at the resin composite/tooth interface during polymerization. The techniques were: bulk filling (B), three horizontal increments (HI), and three wedge increments (WI). A simple Class V cavity preparation was modeled in finite element analysis. Polymerization shrinkage was simulated by a thermal stress analogy, thereby causing 1% shrinkage due to an arbitrary coefficient of thermal expansion. Interface normal and shear stresses were calculated at nine steps during polymerization, proceeding from 0% to 100% volume of cured resin. The importance of the interface transient stresses was revealed by the finding that, in most cases, their peak values exceeded the final or residual stress. Also, the WI and B techniques consistently exhibited the highest and lowest maximum transient stresses, respectively. These results from the simple model of a Class V restoration suggest that bulk filling of light-cured resin composites should be used in restorations which are sufficiently shallow to be cured to their full depth.

Chemical Phenomena↗
PubMed2001

Localization of mandibular changes in patients with class II division 1 malocclusions treated with twin-block appliances: finite element scaling analysis.

Thirty mandibular landmarks were digitized from cephalographs of 46 children (prepubertal, approximately 10 years old) and 53 adolescents (pubertal, approximately 13 years old) to determine mandibular morphological changes in patients with Class II Division 1 malocclusions treated with Twin-block appliances. Procrustes superimposition computed average geometries and an analysis of variance were performed on the cephalographs. Prepubertal pretreatment and approximately 13-month-posttreatment profiles and pubertal pretreatment and approximately 22-month-posttreatment profiles were statistically different (P <.002). In male prepubertal configurations, a color-coded finite element scaling analysis revealed a conspicuous area of positive allometry ( approximately 12%) in the condylar neck and negative allometry ( approximately 17%) at the apex of the coronoid process. For the female prepubertal configuration, local increases in size were discernible in the condylar neck ( approximately 3%) and in the apex of the coronoid process ( approximately 4%). Comparing male pubertal configurations, finite element scaling analysis revealed marked positive allometry ( approximately 27%) in the condylar neck and negative allometry ( approximately 16%) at the apex of the coronoid process. For the female pubertal configurations, local increases in size were noticeable at the condylar neck ( approximately 15%), with negative allometry ( approximately 9%) in the coronoid process. For shape change, all configurations were highly isotropic over the entire mandibular nodal mesh. Therefore, in growing patients treated for Class II Division 1 malocclusions with Twin-block appliances, condylar growth, coronoid process remodeling, and osteogenesis in corpus and dentoalveolar regions may reflect the correction of the underlying skeletal dysmorphology.

Adolescent↗
PubMed2005

Determining diffusion coefficients in inhomogeneous tissues using fluorescence recovery after photobleaching.

Diffusion plays an important role in the transport of nutrients and signaling molecules in cartilaginous tissues. Diffusion coefficients can be measured by fluorescence recovery after photobleaching (FRAP). Available methods to analyze FRAP data, however, assume homogeneity in the environment of the bleached area and neglect geometrical restrictions to diffusion. Hence, diffusion coefficients in inhomogeneous materials, such as most biological tissues, cannot be assessed accurately. In this study, a new method for analyzing data from FRAP measurements has been developed, which is applicable to inhomogeneous tissues. It is based on a fitting procedure of the intensity recovery after photobleaching with a two-dimensional finite element analysis, which includes Fick's law for diffusion. The finite element analysis can account for distinctive diffusivity in predefined zones, which allows determining diffusion coefficients in inhomogeneous samples. The method is validated theoretically and experimentally in both homogeneous and inhomogeneous tissues and subsequently applied to the proliferation zone of the growth plate. Finally, the importance of accounting for inhomogeneities, for appropriate assessment of diffusivity in inhomogeneous tissues, is illustrated.

Algorithms↗
PubMed1997

Finite element stress analysis of IMZ abutment designs: development of a model.

PURPOSE: This article describes the development of a model system for use in finite element stress analysis of three different IMZ abutment designs: original threaded Intra-Mobile Element (IME), Abutment Complete (ABC), and Intra-Mobile Connector (IMC). MATERIALS AND METHODS: A three-dimensional model simulating a cast gold crown restoration attached to an osseointegrated IMZ implant fixture was generated for each abutment design. Each model was discretized into axisymmetric finite elements representing the crown, the various implant system components, and supporting structures. A convergence test was performed to optimize the mesh. Convergence test mesh refinement for the IME, the IMC, and the ABC abutment models resulted in 818 elements, 2,566 nodes; 738 elements, 2,362 nodes; and 663 elements, 2,051 nodes, respectively. Progressive tightening of the retaining screw (preload) was simulated; the degree of screw tightening necessary to prevent opening of the crown-abutment interface in extreme loading (500-N occlusal load at 45 degrees) was determined individually for each system. CONCLUSIONS: Models of three IMZ abutment designs have been refined and the appropriate relative screw preloads determined. This model system is to be used subsequently in stress analysis comparison for the three systems.

Biomechanical Phenomena↗
PubMedDate not supplied

Midfacial morphology of Koreans with class III malocclusions investigated with finite-element scaling analysis.

The spheno-ethmoidal model of midfacial retrognathia suggests that deficient chondrocytic proliferation in the anterior cranial base is associated with inadequate anterior translation of the midfacial complex resulting, for example, in Class III malocclusions. The purpose of this study was to determine whether the morphology of the midface differed in subjects of diverse ethnic origin exhibiting features associated with Class III malocclusions. Lateral cephalographs of 142 children of Korean or European American descent aged between 5 and 11 years were compared. The cephalographs were traced and subdivided into seven age- and sex-matched groups. Average geometries, scaled to an equivalent size, were generated using Procrustes superimposition and subjected to analysis of variance (ANOVA). Graphical analysis using a color-coded finite-element scaling analysis (FESA) program was used to localize differences in morphology. Results indicated that the mean Korean and European American midfacial configurations differed statistically (P < 0.01), and this difference was maintained at most, but not all, age-wise comparisons. Comparing Korean and European American Class III midfacial configurations for local size-change, FESA analysis revealed that while local increases in size were apparent in the posterior palatal regions, the Korean anterior nasal spine regions were generally smaller. For shape-change, the Korean and European American midfacial configurations were predominantly isotropic. Therefore, heterogeneity in appearance may be influenced by morphological variation of the midfacial complex in subjects of diverse ethnic origin, but features of the anterior cranial base may contribute also to the prevalence and severity of Class III malocclusions in Koreans. Moreover, perturbations in endochondral mechanisms of cranio-mandibular growth, and not maxillary intramembranous methods, may be implicated in the etiology of Class III malocclusions in South East Asians.

Age Factors↗
PubMed1997

Modeling the mechanical behavior of the jaws and their related structures by finite element (FE) analysis.

In this paper, we provide a review of mechanical finite element analyses applied to the maxillary and/or mandibular bone with their associated natural and restored structures. It includes a description of the principles and the relevant variables involved, and their critical application to published finite element models ranging from three-dimensional reconstructions of the jaws to detailed investigations on the behavior of natural and restored teeth, as well as basic materials science. The survey revealed that many outstanding FE approaches related to natural and restored dental structures had already been done 10-20 years ago. Several three-dimensional mandibular models are currently available, but a more realistic correlation with physiological chewing and biting tasks is needed. Many FE models lack experimentally derived material properties, sensitivity analyses, or validation attempts, and yield too much significance to their predictive, quantitative outcome. A combination of direct validation and, most importantly, the complete assessment of methodical changes in all relevant variables involved in the modeled system probably indicates a good FE modeling approach. A numerical method for addressing mechanical problems is a powerful contemporary research tool. FE analyses can provide precise insight into the complex mechanical behavior of natural and restored craniofacial structures affected by three-dimensional stress fields which are still very difficult to assess otherwise.

Anatomy, Cross-Sectional↗
PubMed2000

[Three-dimensional finite element stress analysis of supporting bone of mandibular posterior fixed bridge. Part III. Comparative analysis with stress of the cortical bone beneath different pontics of fixed bridge].

OBJECTIVE: To analysis stress of the cortical bone beneath different pontics of mandibular posterior fixed bridge by using three-dimentional finite element method. METHODS: According to the measured data, the characters of all components of fixed bridge and the supporting tissues, and the principals of finite element, the three-dimentional finite element model was developed on the basis of an adult mandible. The model consisted of 1363 nodes and 1134 elements after the fixed bridge was placed. Three different pontics were designed. Young's mudulus and Poisson's ratio were obtained from the literature for each type of tissue or materials in the model. The surfaces of pontic next to the mucosa beneath the pontic consisted of nine elements and the contact area were respectively reduced 1/3. It was assumed all materials in the model were homogeneous, isotropic and linearly elastic. One vertical load of 20 kg and one horizontal load of 20 kg were applied respectively on the occlusal surface of the abutments and the pontics of three different fixed bridge. Three-dimentional finite element stress analysis was used to calculate the epsilon max and the epsilon min of the cortical bone beneath pontics of fixed bridge. RESULTS: Under the vertical loading, the cortical bone beneath the pontics appeared compressive stresses, the stress values of the cortical bone beneath the pontics were respectively -0.211(-)-0.119 (epsilon max, kg/mm2), -0.355(-)-0.201 (epsilon min), -0.224(-)-0.125 (epsilon max), -0.375(-)-0.215 (epsilon min), -0.239(-)-0.133 (epsilon max), -0.395(-)-0.228 (epsilon min). Under the horizontal loading, the cortical bone beneath the pontics exhibited tensile stresses and compressive stresses. The stress values of the cortical bone beneath the pontics were respectively -0.004-0.283 (epsilon max, kg/mm2), -0.249(-)-0.009 (epsilon min), -0.0042-0.301 (epsilon max), -0.264(-)-0.0095 (epsilon min), -0.0045-0.322 (epsilon max), -0.281(-)-0.0101 (epsilon min). The stress in the cortical bone beneath the pontics increased when the area of contact was reduced, the stress values changed in 5%-7%, but the rules of stress distribution of three different pontics were similar. CONCLUSION: Stress values in the cortical bone beneath three pontics are small, and the change of stress in the cortical bone beneath the different pontics of mandibular posterior fixed bridge is small too.

Dental Abutments↗
PubMed2006

Biomechanical consequences of progressive marginal bone loss around oral implants: a finite element stress analysis.

The purpose of this study was to explore the biomechanical effects of progressive marginal bone loss in the peri-implant bone. Finite element model of a Ø 4.1 x 10 mm Straumann dental implant and a solid abutment was constructed as predefined eight-layers around the implant neck. The implant-abutment complex was embedded in a cylindrical bone model to analyze bone biomechanics regardless of anatomical influences. Angular and circular progressive marginal bone loss was simulated by sequential removal of each layer, resulting crater-like defects and a total of ten finite element models for analysis. Each model was subjected to a vertical and oblique static load of 100 N in separate load cases. Principal stress minimum and maximum, displacement, and equivalent of elastic strain outcomes were compared. Under vertical loading, principal stresses minimum and maximum decreased remarkably as with the increase in bone resorption. Under oblique load simulations, decrease in principal stress maximum and minimum was evident. With progressive bone loss and under oblique load simulations, displacement and equivalent of elastic strain increased considerably in trabecular bone contacting the implant neck. The presence of cortical bone contacting a load-carrying implant, even in a bone defect, improves the biomechanical performance of implants in comparison with only trabecular bone support as a sequel of progressive marginal bone loss.

Biomechanical Phenomena↗
PubMed1993

Finite element computations of specific absorption rates in anatomically conforming full-body models for hyperthermia treatment analysis.

Finite element techniques for three-dimensional specific absorption rate (SAR) computation in anatomically based human models are presented. The formulations center on Helmholtz weak forms which have been shown to be numerically robust and to afford additional sparsity in the resulting system of algebraic equations. Practical solution of these equations depends critically on the realization of an effective sparse matrix solver. Experience with several conjugate gradient-type methods is reported. The findings show that convergence rate (and even convergence in some cases) degrades significantly with increasing matrix rank and decreasing electrical loss for mesh spacings which adequately resolve the physical wavelengths of the electromagnetic wave propagation. However, with proper choice of algorithm and preconditioning, reliable convergence has been achieved for matrix ranks exceeding 2 x 10(5) on domains having sizeable volumes of electrically lossless regions. An automatic grid generation scheme for constructing meshes which consist of variable element sizes that conform to a predefined set of boundaries is discussed. Example meshes of homogeneous and heterogeneous human anatomies, the boundaries of which have been derived from CT-scan information, are shown. These results highlight the fact that 3D finite element mesh generation remains a difficult problem, but usable meshes with this level of complexity can be generated. Integration of the finite element formulation, the sparse matrix solver, and the mesh generation scheme is shown to lead to algorithms that can be implemented on inexpensive reduced instruction set computer (RISC) workstations with run times on the order of hours. An example of hyperthermia device simulation is presented which suggests that the finite element method is a practical alternative that rivals the impressive finite-difference time-domain (FDTD) computations that have appeared.

Algorithms↗
PubMed2005

A three-dimensional finite element stress analysis for tunnel placement and buttons in anterior cruciate ligament reconstructions.

This communication reports the results of a three-dimensional finite element (FE) model of stresses in a surgically altered femur and tibia. The model incorporated a novel approach in implementing orthotropic and inhomogeneous bone properties and non-uniform distributed loading. Cortical, cancellous, and subchondral bone of the femur and the tibia were modeled. Mechanical properties for the cortical and cancellous bone were mapped from published data characterizing the anisotropy and inhomogeneity of the bone properties. Mesh adequacy was determined using stress convergence and strain energy error convergence. Qualitatively, the results of the study compare well with experimental principal compressive strains from the literature. With respect to tunnel placement in anterior cruciate ligament reconstruction, the model predicted stress-shielding at the postero-lateral region of the tunnel wall, and increased stress at the postero-medial region of the tunnel wall. The stresses in the cancellous bone beneath the tunnel were, in general, lower than those above the tunnel. Prolonged stress shielding leads to bone resorption of the posterior tunnel wall leading to tunnel enlargement, and possible compromise of the ACL reconstruction. The stresses on the femoral cortex produced from a button-type fixation were noticeable for low levels of loading; the stress levels were very similar in models incorporating bone properties of patients aged 45 and 65. Repeated compression of the femoral cortex at these stress levels may cause microdamage to the cortex eventually resulting in fatigue failure.

Aged↗
PubMedDate not supplied

Effect of Fuji pressure sensitive film on actual contact characteristics of artificial tibiofemoral joint.

OBJECTIVE: To investigate the effect of inserting a Fuji pressure sensitive film into an artificial tibiofemoral joint on the actual contact mechanics. DESIGN: The experimental measurement and finite element analysis were used.Background. Although Fuji pressure sensitive film was widespread used for measuring the contact characteristics of artificial joint, how this measurement approaches actual contact characteristics has not yet been studied extensively. METHOD: Two three-dimensional finite element models of an artificial tibiofemoral joint were constructed. The with-film-model was used to mimic the experimental setup and was verified by comparing the contact area and pressure on the simulated film calculated from finite element analysis to the measured one from the Fuji film (ultra-super low and medium grades) in the experimental test. Then the with-film-model was modified to the without-film-model in which the simulated film was removed. The contact characteristics on the film calculated from the with-film-model were represented to the measured one and the contact characteristics on the tibial component calculated from the without-film-model were represented to the actual one. The measured and actual contact characteristics were studied to investigate the effects of Fuji film on the actual contact characteristics in the tibiofemoral joint of knee prosthesis. RESULTS: The contact characteristics calculated from with-film-model was reasonable agreement with measured one by Fuji film in the experimental test. The maximum difference is 13% in maximum contact pressure under a load of 3000 N. The maximum difference of contact area and pressure between the model simulating actual contact circumstance and the model with inserting a Fuji film between contacting surface are 2.4% and 14% respectively. CONCLUSION: This study revealed that contact area and pressure of the tibiofemoral joint of knee prosthesis measured by Fuji pressure sensitive film could be simulated by finite element analysis. The measurement of contact area in the artificial joint by using ultra-super low grade Fuji film is overestimated its actual contact area by 1.2-2.4%, but the measurement of contact pressure by using medium grade Fuji film is underestimated its actual contact pressure by 8-14%. RELEVANCE: This study revealed that the ultra-super low grade Fuji film is a reliable sensor to measure the contact area and the medium grade film would underestimate its actual contact pressure in the artificial tibiofemoral joint. This finding can provide a better understanding of the reliability of Fuji film to measure the contact characteristics of artificial joint in the experimental test.

Computer-Aided Design↗
PubMed2005

[Stress analysis of the post and core system under loading].

PURPOSE: To analyze the stress of the post and core system by using finite element analysis and study the influence of the "crown materials" on the analytic results. METHODS: Three groups of 3D finite element models of maxillary incisors were established according to the fabricating standard of the post and core system by using I-DEAS finite element analysis software. Group A was consisted of the cast metal post and core, the tooth structure after preparation and the periodontal structure. Group B was composed of the PFM, the cast metal post and core, the tooth structure after preparation and the periodontal structure. Group C was composed of the resin crown, the cast metal post and core, the tooth structure after preparation and the periodontal structure. The three groups were loaded and analyzed under the same loading according to the mean value of the bite force of incisors. RESULTS: (1)The maximum stress of dentin in group A was twice higher than that in group B. The maximum primary stress, minimum primary stress and maximum shear stress of group A were respectively 236.35, 228.83 and 218.05 percent of those in group B. The difference of maximum stress values of group B and group C was neglectable. (2) The maximum stress distribution of dentin in group A and group B was quite different (the stress was concentrated in labial and lingual side of the cervical dentin in group A, otherwise in group B it was concentrated in the area around the alveolar and the labial and lingual side of the dentin which was opposite to the tip of the cast metal post and core). The maximum stress distribution of dentin in group A and group B was almost the same. CONCLUSIONS: Different materials of the crown did not influence the result of 3D finite element stress analysis of the post and core system.

Bite Force↗
PubMed1993

Finite-element stress analysis of the normal and osteoporotic lumbar vertebral body.

A finite-element model of an isolated elderly human L3 vertebral body was developed to study how material properties and loading conditions influence end-plate and cortical-shell displacements and stresses. The model consisted of an idealized geometric representation of an isolated vertebral body, with a 1-mm-thick end plate and cortical shell. For uniform compression, large tensile stresses occurred all around the cortical shell just below the end plate as a result of bending of the cortical shell as it supported the end plate. Large tensile bending stresses also developed in the inferior surface of the end plate. Equal reductions in both trabecular and cortical bone moduli increased displacements but did not affect peak stresses. A 50% reduction in trabecular bone modulus alone increased peak stresses in the end plate by 74%. Elimination of the cortical shell reduced peak stresses in the end plate by approximately 20%. For nonuniform, anteriorly eccentric compression, peak stresses everywhere changed by less than 11% but moved to the anterior aspect. When material properties were adjusted to represent osteoporosis with disproportionate reductions in trabecular (50% decrease) and cortical (25% decrease) bone moduli, anterior compression increased peak stresses by up to 250% compared to uniform compression. If fractures are initiated in regions of large tensile stresses, the results from this relatively simple model may explain how central end-plate and transverse fractures initiate from uniform compression of the end plate. Furthermore, for anterior compression, disproportionate modulus reductions in trabecular and cortical bone may substantially increase end plate and cortical shell stresses, suggesting a cause of age-related spine fractures.

Aged↗