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PubMed1992

Three-dimensional finite element stress analysis of a cantilever fixed partial denture.

A three-dimensional mathematical model was generated, representing a three-unit cantilever fixed partial denture and its supporting mandibular structures. First and second premolars were used as abutments with one posterior cantilever pontic. A 5 lb vertical load was applied to the pontic. Vertical and horizontal stresses were analyzed by means of a three-dimensional finite element stress analysis technique. The results showed that a cantilever pontic creates considerable compressive stress on the abutment nearest to the pontic and produces tensile stress on the abutment farthest from the pontic.

Alveolar Process↗

PubMed2005

An annular prosthesis for the treatment of functional mitral regurgitation: finite element model analysis of a dog bone-shaped ring prosthesis.

BACKGROUND: Undersized annuloplasty is commonly used in the treatment of functional mitral regurgitation. However, in the case of severely dilated ventricles, annuloplasty may be inadequate to counteract leaflet tethering. My colleagues and I hypothesized that modifying the shape of the annular prosthesis to account for the specific anatomy of functional mitral regurgitation could challenge extreme leaflet tethering. METHODS: Using finite element model simulations, we tested valve competence after the implantation of conventional D-shaped versus dog bone-shaped annuloplasty rings, the latter of which was designed to selectively reduce the septolateral dimension of the annulus. Three models were compared: model A, simulating the native mitral valve; model B, simulating the same valve after annuloplasty with a conventional D-shaped annuloplasty; and model C, simulating a dog-bone annuloplasty ring implantation. Each model was then challenged by progressively pulling the tip of the papillary muscles away from the annulus plane to simulate ventricular remodeling and leaflet tethering. Valve competence was compared in each model for each degree of leaflet tethering. RESULTS: After maximal leaflet tethering simulation (4-mm apical displacement of the papillary tips), the regurgitant area increase was 70.4 mm2 for model A and 52.9 mm2 for model B. In model C, the regurgitant area was only negligibly affected by papillary displacement, increasing to 3.9 mm2. CONCLUSIONS: An annular prosthesis with selective reduction in the septolateral dimension is more effective than a conventional prosthesis for treating leaflet tethering in functional mitral regurgitation. Use of disease-specific annular prostheses is needed to improve the results of valve reconstruction.

Animals↗

PubMed2002

Determination of orthotropic bone elastic constants using FEA and modal analysis.

Finite element models have been widely employed in an effort to quantify the stress and strain distribution around implanted prostheses and to explore the influence of these distributions on their long-term stability. In order to provide meaningful predictions, such models must contain an appropriate reflection of mechanical properties. Detailed geometrical and density information is now readily available from CT scanning. However, despite the use of phantoms, a method of determining mechanical properties (or elastic constants) from bone density has yet to be made available in a usable form. In this study, a cadaveric bone was CT scanned and its natural frequencies were measured using modal analysis. Using the geometry obtained from the CT scan data, a finite element mesh was created with the distribution of density established by matching the mass of the FE bone model with the mass of the cadaveric bone. The maximum values of the orthotropic elastic constants were then established by matching the predictions from FE modal analyses to the experimental natural frequencies, giving a maximum error of 7.8% over 4 modes of vibration. Finally, the elastic constants of the bone derived from the analyses were compared with those measured using ultrasound techniques. This produced a difference of <1% for both the maximum density and axial Young's Modulus. This study has thereby produced an orthotropic finite element model of a human femur. More importantly, however, is the implication that it is possible to create a valid FE model by simply comparing the FE results with the measured resonant frequency of the CT scanned bone.

Anisotropy↗

PubMed2004

The influence of occlusal loading location on stresses transferred to implant-supported prostheses and supporting bone: A three-dimensional finite element study.

STATEMENT OF PROBLEM: Information about the influence of occlusal loading by location on the stress distribution in an implant-supported fixed partial denture and supporting bone tissue is limited. PURPOSE: The purpose of this study was to investigate the effect of loading at 1 to 3 different locations on the occlusal surface of a tooth on the stress distributions in an implant-supported mandibular fixed partial denture (FPD) and surrounding bone, using 3-dimensional finite element analysis. MATERIAL AND METHODS: A 3-dimensional finite element model of a mandibular section of bone (Type 2) with missing second premolar and its superstructures were used in this study. A 1-piece 4.1 x 10-mm screw-shape ITI dental implant system (solid implant) was modeled for this study. Cobalt-Chromium (Wiron 99) was used as the crown framework material and porcelain was used for occlusal surface. The implant and its superstructure were simulated in a Pro/Engineer 2000i program. Total loads at 300 N were applied at the following locations: 1) tip of buccal cusp (300 N); 2) tip of buccal cusp (150 N) and distal fossa (150 N); or 3) tip of buccal cusp (100 N), distal fossa (100 N), and mesial fossa (100 N). RESULTS: The results demonstrated that vertical loading at 1 location resulted in high stress values within the bone and implant. Close stress levels were observed within the bone for loading at 2 locations and 3 locations; the former created the most extreme stresses and the latter the most even stresses within the bone. With loading at 2 or 3 locations, stresses were concentrated on the framework and occlusal surface of the FPD, and low stresses were distributed to the bone. CONCLUSION: For the loading conditions investigated, the optimal combination of vertical loading was found to be loading at 2 or 3 locations which decreased the stresses within the bone. In this situation, von Mises stresses were concentrated on the framework and occlusal surface of the FPD.

Aluminum Silicates↗

PubMedDate not supplied

Finite element stress analysis of the influence of staggered versus straight placement of dental implants.

Bending moments resulting from non-axial overloading of dental implants may cause stress concentrations exceeding the physiologic supporting capacity of cortical bone, leading to various kinds of failures. The aim of this study was to evaluate the effect of staggered (offset, tripodization) implant placement configuration and placement of wider-diameter implants in a straight-line configuration in mandibular posterior edentulism. A mandibular Kennedy Class II partially edentulous finite element model was constructed. Seven different partial fixed prostheses supported by 3 implants were designed according to 2 main configurations: straight-line or staggered implant placement. In 5 of the designs, implants with various diameters and length were placed along a straight line. In the other 2 models, offset placement of the middle implant buccally and lingually was simulated. A 400 N static load was applied perpendicular to the buccal inclination of the buccal cusps on each unit. Tensile and compressive stress values on cortical bone in the cervical region of the implants were evaluated. Lower stress values were recorded for the configuration with wider implants placed in a straight line. Other configurations, including staggered implant placement, produced similar stress values. Despite the offset implant placement, the stresses were not decreased; however, straight placement of wider implants may decrease bending moments.

Compressive Strength↗

PubMed2005

Analysis of the effects of different materials in a tooth implant-supported fixed prosthesis using finite element method.

In this study, design optimization of a tooth implant-supported fixed prosthesis was investigated theoretically. A three-dimensional finite element analysis was utilized to simulate the stress distribution and deformation, with an emphasis on the material selection for various parts of the prosthesis. This mandibular prosthesis was supported by six implants. The properties of 3 different materials for implants and 4 different materials for framework were incorporated into 12 different models. For the loading conditions used, it was found that the largest displacements occurred at the far ends of the framework and that the resulting deflection was highly dependent on the material properties of the framework. The simulations showed that the stress in the framework was mainly concentrated near the holes in the lower surface and that the highest values of von Mises stresses occurred in the lingual part of the prosthesis. Furthermore, the modeling results revealed that more rigid frameworks led to a corresponding decreased stress in the retaining screws and that high-stress concentration areas moved from the neck of the implant towards the base of it, as the value of Young's modulus increased. It was concluded that the first best model was the Cr-Co alloy for the framework and the Ti alloy for the implant and the second best choice was the Cr-Co alloy for both the framework and the implant.

Computer Simulation↗

PubMed2000

Evaluation of stresses caused by dentin pin with finite elements stress analysis method.

The aim of the present study was to show the dimensions and the amount of stresses caused by pins on dentin. Mathematically modelled stainless steel and titanium pins were applied to mandibular first molar teeth with extensive crown destruction. The stress caused by the pins was examined with the finite elements method (FEM). In both types of pin, the maximum diffuse and the dense stress areas were located at the bottom of the pin channel. It is believed that these stresses should be taken into consideration when evaluating the advantages and disadvantages of pin application to teeth with destroyed crowns.

Alveolar Process↗

PubMed1999

Finite element stress analysis on the effect of splinting in fixed partial dentures.

STATEMENT OF PROBLEM: Long-span fixed partial dentures usually require splinting of multiple abutments to overcome mechanical problems associated with the long edentulous span. Most information and indications for the use of multiple splinted abutments have been empirically derived. PURPOSE: This study analyzed the stress levels in the teeth and supporting structures of a fixed prosthesis and ascertained how the addition of multiple abutments in a fixed prosthesis modifies the stresses and their deflection. MATERIAL AND METHODS: The finite element method was used to analyze mechanical behaviors of a prosthesis and its supporting structures when a fixed prosthesis with several designs replaced a mandibular second premolar and a first molar. Variations of the standard finite element model were made by changing the number of splinted teeth and the level of bone support. RESULTS: A reduction of stress and deflection was observed in the supporting structures when a fixed partial denture was fabricated and teeth were splinted together. Increasing the number of splinted abutments did not reveal a proportional reduction of stress in the periodontium. Stress concentrations were seen in the connectors of prosthesis and in the cervical dentin area near the edentulous ridge. CONCLUSION: Increasing the number of the splinted abutment did not compensate for the mechanical problems of a long-span fixed partial denture sufficiently.

Alveolar Bone Loss↗

PubMed2002

Mechanical conditions in the internal stabilization of proximal tibial defects.

OBJECTIVES: The goal was to design a method which would permit an assessment of the suitability of a newly developed implant under physiological-like loading conditions. Information obtained from such an analysis is expected to delineate more clearly the indications for a new device prior to clinical utilization. DESIGN: In vitro mechanical stiffness testing and finite element analysis. METHODS: From in vitro testing of proximal tibiae with defects, the stiffness of an internal stabilization system was determined. Using a finite element model, the loading of both the implant and bone was analyzed including all muscle forces. The variation in implant loading and interfragmentary strain for different defect locations was also investigated. RESULTS: Conventional stiffness testing demonstrated the comparability of the experimental findings with the finite element predictions. Under physiological-like loading the implant experienced high bending and von Mises stresses if defects in the region of the shaft were stabilized. A short working length increased implant loading up to the yield strength of the material. CONCLUSIONS: The finite element analysis illustrated the appropriateness of this new device for proximal defects of the tibia, but the implant should be used with hesitation in fractures or defects extending into the diaphyseal region of the bone. RELEVANCE: This new analytical approach helped to identify clinical indications for the implant in which its mechanical attributes would prove advantageous.

Biomechanical Phenomena↗

PubMed1996

Stress and strain distribution within the intact femur: compression or bending?

The aim of this research was to test the hypothesis that the intact femur is loaded predominately in compression. The study was composed of two parts: a finite element analysis of the intact femur to assess if a compressive stress distribution could be achieved in the diaphyseal region of the femur using physiological muscle and joint contact forces; a simple radiological study to assess the in vivo deflections of the femur during one legged stance. The results of this investigation strongly support the hypothesis that the femur is loaded primarily in compression, and not bending as previously thought. The finite element analysis demonstrated that a compressive stress distribution in the diaphyseal femur can be achieved, producing a stress distribution which appears to be consistent with the femoral cross-sectional geometry. The finite element analysis also predicted that for a compressive load case there would be negligible deflections of the femoral head. The radiological study confirmed this, with no measurable in vivo deflection of the femur occurring during one legged stance.

Adult↗

PubMed1995

Location of the centre of resistance for the nasomaxillary complex studied in a three-dimensional finite element model.

The purpose of this study was to investigate the location of the centre of resistance (CRe) for the nasomaxillary complex by the use of finite element analysis. A three-dimensional finite element model of the craniofacial complex, consisting of 2918 nodes and 1776 elements, was used for displacement analyses. Anteriorly and inferiorly directed forces of 9.8 N were applied at five different levels, parallel and perpendicular to the functional occlusal plane, respectively. For each loading condition, horizontal and vertical displacements of eight anatomic points in the complex and on the maxillary dentition were analysed. The complex exhibited an almost translatory displacement of approximately 1.0 microns in the forward direction when the horizontal force was applied at a point on the horizontal plane, passing through the superior ridge of the pterygomaxillary fissure, whereas the complex experienced clockwise or counter clockwise rotation when the forces were applied at the remaining levels. Furthermore, the downward forces produced anteriorly upward, or posteriorly upward rotation. However, the force applied at a point on the vertical plane passing through the posterior wall of the pterygomaxillary fissure, produced almost equal displacements of approximately 6.0 microns in an inferior direction for all the anatomic points. It is suggested that CRe of the nasomaxillary complex is located on the posterosuperior ridge of the pterygomaxillary fissure, registered on the median sagittal plane.

Biomechanical Phenomena↗

PubMed1995

A three-dimensional finite-element stress analysis of an endodontically prepared maxillary central incisor.

This study is an application of a three-dimensional Finite-Element Method to investigate the changes in stress characteristics of a prepared maxillary central incisor. The purpose of this study was to analyze stress distributions in this tooth after simulated canal preparation and static loading. A maxillary central incisor was embedded in acrylic, sectioned, photographed, and digitized. A three-dimensional finite-element model was generated by a computer and appropriately modified to simulate canal preparation. Data identified the highest stress magnitudes to be located between the middle and coronal thirds of the root; an area clinically observed to be prone to fracture during treatment. In addition, the magnitude of generated stresses was directly correlated with the simulated prepared canal diameter. The development of a validated three-dimensional finite-element method could identify areas that may predispose a tooth to structural failure during condensation loads.

Computer Simulation↗

PubMedDate not supplied

Finite element stress analysis of the crowns of normal and restored teeth.

Stress distributions are presented for a normal and a restored mandibular second premolar under masticatory-type forces. These were obtained using the finite element method of stress analysis applied to two-dimensional models. The effect of the relative stiffness of the materials is examined in each instance.

Bicuspid↗

PubMed2003

Burst fracture in the metastatically involved spine: development, validation, and parametric analysis of a three-dimensional poroelastic finite-element model.

STUDY DESIGN: A finite-element study and in vitro experimental validation was performed for a parametric investigation of features that contribute to burst fracture risk in the metastatically involved spine. OBJECTIVES: To develop and validate a three-dimensional poroelastic model of a metastatically compromised vertebral segment, to evaluate the effect of lytic lesions on vertebral strains and pressures, and to determine the influence of loading and motion segment status (bone density, pedicle involvement, disc degeneration, and tumor size) on the relative risk of burst fracture initiation. SUMMARY OF BACKGROUND DATA: Finite-element analysis has been used successfully to predict failure loads and fracture patterns for bone. Although models for vertebra affected with tumors have been presented, these have not been thoroughly validated experimentally. Consequently, their predictive capabilities remain uncertain. METHODS: A three-dimensional poroelastic finite-element model of the first lumbar vertebra and adjacent intervertebral discs, including a tumor of variable size, was developed. To validate the model, 12 cadaver spinal motion segments were tested in axial compression, in intact condition, and with simulated osteolytic defects. Features of the validated model were parametrically varied to investigate the effects of tumor size, trabecular bone density, pedicle involvement, applied loads, loading rates, and disc degeneration using outcome variables of vertebral bulge and vertebral axial deformation. RESULTS: Consistent trends between the experimental data and model predictions were observed. Overall, the model results suggest that tumor size contributes most toward the risk of initiating burst fracture, followed by the applied load magnitude and bone density. CONCLUSIONS: The parametric analysis suggests that the principal factors affecting the initiation of burst fracture in metastatically affected vertebrae are tumor size, magnitude of spinal loading, and bone density. Consequently, patient-specific measures of these factors should be factored into decisions regarding clinical prophylaxis. Pedicle involvement or disc degeneration was less important according to the outcome measures in this study.

Adult↗

PubMed2004

Identification of the piezoelectric material coefficients using the finite element method with an asymptotic waveform evaluation.

A rapid identification of the piezoelectric material constants for a piezoelectric transducer is proposed. The validity of a three-dimensional finite element routine was confirmed experimentally. The asymptotic waveform evaluation (AWE) was adopted for a fast frequency sweep of the finite element analysis. The three-dimensional finite element method with an AWE and a design sensitivity method was used for a material inversion scheme of piezoelectric transducers. In order to confirm the inversion routine of the material constants, the mechanical displacements, which mean the mode shape, were calculated along the vertical and lateral position of the sample transducer.

Journal Article↗

PubMed2002

The effects of tibial component inclination on bone stress after unicompartmental knee arthroplasty.

Unlike the case with total knee arthroplasty, the femorotibial angle (FTA) after unicompartmental knee arthroplasty (UKA) does not directly depend on the inclination of the tibial component when the height of the joint line is maintained. This study analyzed the effects of the inclination of the tibial component in the coronal plane on the contact pressure of the implant-bone surface and the stresses on the proximal tibia. A two-dimensional, coronal plane model of the proximal tibia was subjected to finite-element analysis. Sixteen patterns of finite-element models of equal FTA were developed in which the inclination of tibial components ranged from 5 degrees valgus to 10 degrees varus in increments of 1 degrees. Stress concentration at the proximal medial diaphyseal cortex gradually increased as the inclination changed from valgus to varus. Maximum contact pressure on the metal-bone interface similarly changed and shifted from the lateral edge to the medial edge of the implant as the inclination changed to varus. It was found that even without changing FTA, the inclination of the tibial component might affect stress concentration and contact pressure in the proximal tibia after UKA. The results suggested that slight valgus inclination of the tibial component might be preferable to varus and even to 0 degrees (square) inclination so far as the stress distribution is concerned.

Arthroplasty, Replacement, Knee↗

PubMed1995

Effect of porous coating and loading conditions on total hip femoral stem stability.

An examination of femoral bone-prosthesis interface behavior under different load types is undertaken using finite-element analysis. Three-dimensional finite-element models are made of two designs of hip prostheses after implantation in a femur. Femoral geometry was determined by computed tomography scans. The models were loaded in one-legged stance and stairclimbing configurations. The implants were modeled as both smooth surfaced and porous coated. The amount of contact and the relative motion between bone and implant were calculated. It is shown that torsional loads such as occur during stairclimbing contribute to larger amounts of implant micromotion than does stance loading. Contact at the bone-prosthesis interface is more dependent on load type than on implant geometry or surface coating type.

Biomechanical Phenomena↗

PubMed1999

Correlation between pre-operative periprosthetic bone density and post-operative bone loss in THA can be explained by strain-adaptive remodelling.

Periprosthetic adaptive bone remodelling after total hip arthroplasty can be simulated in computer models, combining bone remodelling theory with finite element analysis. Patient specific three-dimensional finite element models of retrieved bone specimens from an earlier bone densitometry (DEXA) study were constructed and bone remodelling simulations performed. Results of the simulations were analysed both qualitatively and quantitatively. Patterns of predicted bone loss corresponded very well with the DEXA measurements on the retrievals. The amount of predicted bone loss, measured quantitatively by simulating DEXA on finite element models, was found to be inversely correlated with the initial bone mineral content. It was concluded that the same clinically observed correlation can therefore be explained by mechanically induced remodelling. This finding extends the applicability of numerical pre-clinical testing to the analysis of interaction between implant design and initial state of the bone.

Absorptiometry, Photon↗