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PubMed1975

Finite element analysis of dental structures--axisymmetric and plane stress idealizations.

The finite element method used to study stress generated in a maxillary second premolar as a result of occlusal forces. This mathematical technique has been applied extensively in structural engineering and structural mechanics. It is well suited to the analysis of stress in teeth and dental restorations because it can closely simulate the geometries, loads, and material inhomogeneities in the system being studied.

Dental Stress Analysis↗
PubMed1991

The role of axial rotation in the etiology of unilateral disc prolapse. An experimental and finite-element analysis.

This study was done to establish the relevance of axial rotation as a cause of disc degeneration in the lumbar spine and the role of facet asymmetry in the injury mechanism. It previously was shown that facet asymmetry does not affect the axial torque-rotation response of lumbar motion segments. This study, in both an experimental and a finite-element analysis, examined three important points previously not considered for lumbar motion segments subjected to axial torque: 1) the effect of facet asymmetry on the coupled motions; 2) the effect of combined geometric parameters on the segment response; and 3) the effect of facet asymmetry on the annular strains. Three different lumbar-coupling patterns were observed; however, they did not appear to be influenced by facet joint asymmetry. An oblique and flat compression facet may allow an increased motion-segment response, but in general, combined geometric parameters were found to have no effect on segment response. It was concluded that, without facet damage, the right or left side of the disc is not biased by a particular facet geometry to experience unusual levels of stress and strain, either as a result of increased axial rotation or any of the associated coupled motions.

Cadaver↗
PubMed2003

Finite element analysis of strength characteristics of various resin based restorative materials in Class V cavities.

This study investigated the strength characteristics of various composites (Tetric Ceram, Tetric Flow, Prisma AP.H, Synergy Duo Shade, Synergy Compact, and Z 100) and compomers (Compoglass, Compoglass F, Dyract AP, F 2000) that were applied in a Class V cavity of a maxillary central incisor. The study was conducted by using a 3-dimensional finite element approach and in the study ansys package program was used. The tooth model had 294 elements and 420 nodes. The teeth considered were assumed to be subjected to an incisal load of 200 N acting at an angle of 26 degrees with the longitudinal axis of the tooth but the effects of different loading angles and different loads were also analysed. Hence, the loads of 100 and 400 N and the loading angles of 0 degrees representing bruxism and 90 degrees representing a traumatic load were also taken into consideration. The effects of the cavity preparation size were also studied. It was determined that any increase in the loading angle and/or the amount of the load resulted in a proportional increase in the stresses developed in the tooth. Furthermore it was also verified that, as a cavity weakens the tooth structure by creating a discontinuity in an intact tooth, the larger sized cavity preparations inevitably cause larger stresses to be developed in the tooth. Strictly from the mechanical point of view, the stresses developed in the restored teeth were determined to be inversely proportional with the modulus of elasticity of the restorative materials. Therefore within the scope of the study Z 100 was found to be superior to the other materials concerned.

Compomers↗
PubMed2001

The influence of the restoration-tooth interface in light cured composite restorations: a finite element analysis.

This study examines the early shrinkage behaviour of dental composite resins, and in particular the interfacial stresses around the margins of a composite restoration. The development of stresses at the restoration-tooth interface can have a detrimental effect on the longevity of a restoration. The influence of this interface on the stress system generated in the tooth was examined using finite element analysis. The restoration-tooth interface was simulated using spring elements of varying spring constants (k = 1, 10(2), 10(4), 10(10) N/mm). Interfacial stresses varied from -0.15 to 0.42 MPa for a spring constant of 1 N/mm, and from -19 to 68 MPa for a spring constant of 10(10) N/mm. Correlations between stiffness at the restoration-tooth interface and higher shrinkage stresses due to restricted shrinkage were found. Interfacial failure at the upper and lower regions of the interface, as well as cuspal movements of the order of 2 microm were predicated for the model of the highest spring constant, 10(10) N/mm. The restoration-tooth interface modelled by the spring elements was seen to have a conclusive effect on the ensuing stress system, as well as the longevity of the restoration.

Acrylic Resins↗
PubMed2006

Transient finite element analysis of electric double layer using Nernst-Planck-Poisson equations with a modified Stern layer.

A finite element implementation of the transient nonlinear Nernst-Planck-Poisson (NPP) and Nernst-Planck-Poisson-modified Stern (NPPMS) models is presented. The NPPMS model uses multipoint constraints to account for finite ion size, resulting in realistic ion concentrations even at high surface potential. The Poisson-Boltzmann equation is used to provide a limited check of the transient models for low surface potential and dilute bulk solutions. The effects of the surface potential and bulk molarity on the electric potential and ion concentrations as functions of space and time are studied. The ability of the models to predict realistic energy storage capacity is investigated. The predicted energy is much more sensitive to surface potential than to bulk solution molarity.

Chemistry, Physical↗
PubMed1998

Three-dimensional finite element analysis of thermal shock in a premolar with a composite resin MOD restoration.

A three-dimensional finite element model of a human premolar with a composite resin Class II MOD has been used to investigate the temperature changes and induced thermal stresses associated with the imbibing of a hot liquid. Regions of high tensile stress were revealed and their possible clinical significance with respect to microleakage and failure in the approximal region of the restoration are discussed.

Bicuspid↗
PubMed2006

Determination of lamb wave dispersion data in lossy anisotropic plates using time domain finite element analysis. Part II: application to 2-2 and 1-3 piezoelectric composite transducer arrays.

The use of finite element modeling, combined with optical generation and detection of Lamb waves in plate structures, was extended to encompass periodic ceramic-polymer materials typical of those encountered in 1-3 and 2-2 piezoelectric composite array transducers. The resultant dispersion data was employed to predict the occurrence of Lamb wave-induced cross talk in composite monolithic arrays. The finite element modeling method was then used to simulate the dispersion behavior of two array structures that were subsequently manufactured: a 1-D 45% volume fraction linear array coupon and a 2-D 35% volume fraction array coupon. Excellent agreement between theory and experiment was obtained using impedance measurements and laser scans of the surface displacement profile at selected frequencies. Regions of strong inter-element cross-coupling were identified and these are shown to correlate very well with the dispersion data obtained for the dual-phase plate material. This work is considered to provide a useful basis for the design of wideband monolithic composite arrays and minimization of guided wave propagation along the array substrate.

Anisotropy↗
PubMedDate not supplied

Factors which may increase stresses at the pin-bone interface in external fixation: a finite element analysis study.

The pin-bone interface of the external fixation system has been studied using a finite element mode. The maximum stresses were observed in the near 'cortex' adjacent to the site of entry of the pin. This location coincides with the area where loosening is usually first observed radiologically. Other results indicate that the stress values are significantly increased by using deep threads and by using stainless steel instead of titanium.

Biomechanical Phenomena↗
PubMed1998

Cementless implant composition and femoral stress. A finite element analysis.

Proximal atrophy and thigh pain are recognized problems with some cementless femoral stems in total hip arthroplasty. It is thought that reduced femoral stress from alterations in load transfer caused by an intramedullary stem contributes to proximal femoral atrophy. An increase in flexural rigidity and bone stress near the stem tip is thought to contribute to thigh pain. A three-dimensional finite element analysis study was performed to calculate stresses in the proximal femur and bone near the stem tip before and after implantation of a collared, proximally coated, cementless femoral prosthesis. The influence of prosthetic material was examined by changing implant composition from cobalt chrome to titanium alloy and leaving all other parameters constant. Femoral stress was increased twofold immediately below the collar with the titanium implant compared with the cobalt chrome. However, the proximal femoral stress in the titanium implanted model was still 1/10 that in the corresponding region of the unimplanted femur model. At the stem tip, as much as a 30% reduction in femoral stress was seen with the titanium stem compared with the cobalt chrome. These findings suggest biomechanical evidence of an advantage for titanium as an implant material compared with cobalt chrome for cementless femoral stems.

Cementation↗
PubMed2000

Clinical and finite element analysis of a modular femoral prosthesis consisting of a head and stem component in the treatment of pertrochanteric fractures.

OBJECTIVE: To determine the biomechanical characteristics and potential clinical efficacy of a cementless modular femoral prosthesis consisting of a variable head (50 to 80 millimeters) and stem (length 120 to 280 millimeters, diameter 10 to 20 millimeters) component in patients with pertrochanteric femoral fracture. DESIGN: Finite element analysis (FEA) of different lengths and diameters of prosthesis components and first clinical prospective study in pertrochanteric femoral fracture. METHOD: Using a 3D-CAD program, a model of femoral cortical bone with a pertrochanteric fracture was created and combined with a model of the prosthesis. This model was transferred into an FEA program. After applying a torsion-bending load of 2,000 N (25 degrees, 45 degrees) on the prosthesis, stress distribution in the cortical bone was determined for different lengths (160 to 240 millimeters) and diameters (10 and 12 millimeters) of stem. PATIENTS: Twenty-eight patients with pertrochanteric fractures (very unstable or osteoarthritis) were treated with a modular hip arthroplasty. Complications, fracture healing, and results at first follow-up (average 13 months) were determined. RESULTS: FEA analysis indicated that reduction in stress was less when a prosthesis with a short stem was used. Shear stress in the interface bone/prosthesis was not affected by stem length. Prostheses with thin stems produced higher sheer stresses than those with thick stems. Results of FEA were used as the basis for clinical application of the device. None of the patients died, and all patients were able to walk, although some needed a cane or walker after surgery. There was no increase in thigh pain compared with reported pretrauma levels. Radiographs showed subsidence of up to 5 millimeters in 20 percent of patients. However, all but one prosthesis was stable at follow-up. Fracture healing was achieved in all patients. CONCLUSIONS: If proximal fixation of a femoral uncemented stem cannot be achieved, stem diameter should provide maximum cortical contact to reduce sheer stress. Longer stems do not necessarily provide additional stability. By using this prosthesis and selection method, a good outcome at first follow-up was observed.

Activities of Daily Living↗
PubMed2006

Finite element analysis of the resurfaced femoral head.

Failure of the resurfaced femoral head may occur in the short term owing to femoral neck fracture or in the long term owing to aseptic loosening as a result of strain shielding. Resurfacing arthroplasties are not all the same. In particular, there is considerable debate regarding the role of the metaphyseal stem and cementing technique. This study examines the influence of various metaphyseal stem configurations (diameter, percentage length in contact with bone, and bonded versus debonded) and cement mantle thickness on the load transfer within the femoral head. Resurfacing resulted in significant strain shielding in the superior femoral head and elevated strain in the superior femoral neck. Although the increase in strain in the femoral neck was significant, the mean strains were below the yield strain for cancellous bone. Peak strains were observed above the yield strain, but they accounted for less than 1 per cent of the total head-neck bone volume and therefore were unlikely to result in femoral neck fracture. Increasing the stem diameter and increasing the percentage stem length in contact with bone both increased the degree of strain shielding. Bonding the metaphyseal stem produced the most dramatic strain shielding, which also extended into the head-neck junction. In contrast, varying the cement mantle thickness had a negligible effect on the load transfer.

Biocompatible Materials↗
PubMed2006

Evaluation of the biomechanical behavior of maxillary central incisors restored by means of endocrowns compared to a natural tooth: a 3D static linear finite elements analysis.

OBJECTIVE: The present study aimed at evaluating different restoring configurations of a crownless maxillary central incisor, in order to compare the biomechanical behavior of the restored tooth with that of a sound tooth. MATERIALS AND METHODS: A 3D FE model of a maxillary central incisor is presented. An arbitrary static force of 10 N was applied with an angulation of 125 degrees to the tooth longitudinal axis at level of the palatal surface of the crown. Different material configurations were tested: composite, syntered alumina, feldspathic ceramic endocrowns and glass post resorations with syntered alumina and feldspathic ceramic crown. RESULTS: High modulus materials used for the restoration strongly alter the natural biomechanical behavior of the tooth. Critical areas of high stress concentration are the restoration-cement-dentin interface both in the root canal and on the buccal and lingual aspects of the tooth-restoration interface. Materials with mechanical properties underposable to that of dentin or enamel improve the biomechanical behavior of the restored tooth reducing the areas of high stress concentration. SIGNIFICANCE: The use of endocrown restorations present the advantage of reducing the interfaces of the restorative system. The choice of the restorative materials should be carefully evaluated. Materials with mechanical properties similar to those of sound teeth improve the reliability of the restoartive system.

Aluminum Oxide↗
PubMed2003

Influence of the stiffness of bone defect implants on the mechanical conditions at the interface--a finite element analysis with contact.

The study focused on the influence of the implant material stiffness on stress distribution and micromotion at the interface of bone defect implants. We hypothesized that a low-stiffness implant with a modulus closer to that of the surrounding trabecular bone would yield a more homogeneous stress distribution and less micromotion at the interface with the bony bed. To prove this hypothesis we generated a three-dimensional, non-linear, anisotropic finite element (FE) model. The FE model corresponded to a previously developed animal model in sheep. A prismatic implant filled a standardized defect in the load-bearing area of the trabecular bone beneath the tibial plateau. The interface was described by face-to-face contact elements, which allow press fits, friction, sliding, and gapping. We assumed a physiological load condition and calculated contact pressures, shear stresses, and shear movements at the interface for two implants of different stiffness (titanium: E=110GPa; composite: E=2.2GPa). The FE model showed that the stress distribution was more homogeneous for the low-stiffness implant. The maximum pressure for the composite implant (2.1 MPa) was lower than for the titanium implant (5.6 MPa). Contrary to our hypothesis, we found more micromotion for the composite (up to 6 microm) than for the titanium implant (up to 4.5 microm). However, for both implants peak stresses and micromotion were in a range that predicts adequate conditions for the osseointegration. This was confirmed by the histological results from the animal studies.

Animals↗
PubMed1997

Three-dimensional finite element analysis of the retention of fixed partial dentures.

Four three-dimensional mathematical models were generated, each representing a three-unit fixed partial denture. The second premolar and second molar were used as abutments. Different associations of dental support preparation were tested. A 500-N axial load was applied to the pontic. Strains were analysed for each dental support by means of a three-dimensional finite element analysis technique. The results showed that the greatest strains were observed on the weaker abutment, the premolar. The cervical margin facing the edentulous area is affected most, regardless of the model or the dental support. The greater the dento-prosthetic differential surface between the two dental supports (thus the greater the retention differential) the higher the risk of unsealing.

Bicuspid↗
PubMed2004

Abutment forms and restorative materials in adhesive prosthesis: a finite element analysis.

This study evaluated experimental abutment forms utilizing adhesion for clinical treatment by the three-dimensional finite element method. Three experimental abutment forms with no axial wall were evaluated: Form 1 was the occlusal surface reduced by 1.5 mm, Forms 2 and 3 were the crown cut perpendicular to the tooth axis 2 mm or 4 mm from the central groove. The restorations were made of 3 types of materials: composite resin, porcelain, and a gold-based alloy. Restorations were bonded to the abutments with an adhesive resin. A vertical load of 500 N was applied to the center of the inner incline of the buccal cusp. The stresses in the adhesives were largest in Form 1 with composite resin and in Form 3. It was indicated that the stresses were greatly affected by the form of the abutment and the restorative materials.

Bicuspid↗
PubMed1997

Estimating the effective Young's modulus of soft tissues from indentation tests--nonlinear finite element analysis of effects of friction and large deformation.

A nonlinear finite element model was developed to investigate the biomechanics of indentation, particularly the influence of friction and large deformation on the calculation of the effective Young's modulus from the cylindrical, flat-ended indentation test of soft tissues. A new kappa table was given for calculation of the effective Young's modulus to account for the effects of layered geometry with consideration of the larger deformation. The results indicate that the effect of friction on the calculation of Young's modulus becomes significant with a large aspect ratio and with a large Poisson's ratio. It is found that the factor kappa increases almost proportionally to the increase of the indentation depth, especially obvious with a larger Poisson's ratio v and a larger aspect ratio a/h.

Elasticity↗
PubMed2004

Finite-element analysis of contact between elastic self-affine surfaces.

Finite-element methods are used to study nonadhesive, frictionless contact between elastic solids with self-affine surfaces. We find that the total contact area rises linearly with the load at small loads. The mean pressure in the contact regions is independent of load and proportional to the root-mean-square slope of the surface. The constant of proportionality is nearly independent of the Poisson ratio and roughness exponent and lies between previous analytic predictions. The contact morphology is also analyzed. Connected contact regions have a fractal area and perimeter. The probability of finding a cluster of area a(c) drops as a(-tau )(c ) where tau increases with a decrease in roughness exponent. The distribution of pressures shows an exponential tail that is also found in many jammed systems. These results are contrasted to simpler models and experiments.

Journal Article↗