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PubMed2000

Stress distribution in the temporomandibular joint affected by anterior disc displacement: a three-dimensional analytic approach with the finite-element method.

The purpose of this study was to investigate the influences of anterior disc displacement on TMJ loading during maximum clenching by use of finite-element analysis. Based on a young human dry skull, an analytic model of the mandible including the TMJ was developed. In addition to the standard model with normal disc-condyle relation, two models were designed to simulate various degrees of anterior disc displacement. In the standard model, compressive stresses were induced in the anterior, middle and lateral areas on the condyle and glenoid fossa, whereas tensile stresses were observed in the posterior and medial regions. In the models with anterior disc displacement, compressive stresses were recognized in all the areas of TMJ components excluding the bilaminar zone. Shear stresses in the articular disc and bilaminar zone significantly increased in most areas. In conclusion, stress distributions in the TMJ with a normal disc position was substantially different from those with anterior disc displacement, suggesting that the progress in disc displacement may have some association with the nature of stress distributions in the TMJ, in the articular disc in particular.

Bite Force↗

PubMed2003

[The 3D finite element stress analysis of transtibial monolimb].

In this study, a 3D model of a transtibial monolimb and residual limb was constructed. The stresses on all nodes of the model under the simulus of the load at the Mid-Stance were computed through 3D finite element analysis (FEA). The stress distribution on the internal and external surfaces of the model was obtained. The results indicate that the stresses on socket are lower than those on prosthetic shank; high stress regions are located on the underneath of prosthetic shank and the border section of socket and prosthetic shank. These data will be useful for CAD\CAM system of monolimb designing.

Artificial Limbs↗

PubMed2004

Influences of the temporal nature of the applied load and the tibial baseplate material on the stress distribution in a three-dimensional model of the human knee joint containing a prosthetic replacement.

The finite element analysis method was used to determine the stresses in all sections of a three-dimensional model of the proximal section of the human knee joint into which was cemented two parts of a total knee joint replacement (the tibial tray and the tibial baseplate), fully constrained at its distal end, and subjected to a total compressive joint force of 2 kN acting on points corresponding to the condyles. When the mean values of these stresses were computed for all sections of the model, two important trends were seen. First, when the load was applied dynamically, the stresses were between 1 and 20% different than when it acted quasi-statically. Second, regardless of how the load was applied, the stresses when the tibial baseplate was considered fabricated from ultra-high-molecular-weight polyethylene ranged from about 40% lower to about 320% higher compared to when Ti-13Nb-13Zr alloy was used. The significance of these findings as well as the limitations of the study are discussed.

Adaptation, Physiological↗

PubMed2003

Optimization of the geometry of total knee implant in the sagittal plane using FEA.

The aim of this research was to investigate the optimization of the geometry of an UHMWPE type of knee implant in the sagittal plane with minimum amount of wear. Finite element analysis has been used to analyze our proposed 780 models consisting of different design parameters. Maximum stress occurring in the whole tibial component, on the surface or subsurface of the plate, was considered as a design parameter to evaluate the wear condition. By avoiding the small contact area and high stresses in the tibial part, the maximum safe flexion angles have been determined. Other effective design factors such as implant stability, roll back distance, patella lever arm, and minimum bone resection have also been considered. Taking into account the variable parameters in the geometry of the implant parts, all possible models for the femoral component, which is made from metal, and the tibial component, which is made from UHMWPE, have been built in ANSYS and analyzed in the sagittal plane. By considering the effective mechanisms of wear in polyethylene, the results of the analyses were used to find the optimized geometry of a knee implant. This is the model, which is expected to experience the minimum wear, besides having some other properties of an ideal knee prosthesis.

Computer Simulation↗

PubMedDate not supplied

Effects of mesiodistal inclination of implants on stress distribution in implant-supported fixed prostheses.

PURPOSE: Patterns of von Mises stress values surrounding implants supporting fixed prostheses in the posterior edentulous maxilla were evaluated using 3-dimensional finite element analysis. MATERIALS AND METHODS: Implants were placed in maxillary bone in 2 different configurations. In the first configuration, implants were placed in the first premolar, second premolar, and second molar regions; in the second configuration, implants were placed in the second premolar and second molar regions, and a mesial cantilever was extended to the space of the first premolar tooth on the superstructure. On the implant placed in the socket of the second molar, 3 different inclinations were used (0, 15, and 30 degrees). Loading was applied in the vertical, oblique, and horizontal axes. RESULTS: Inclination of the implant in the molar region was found to result in increased stress. Significant increase in stress on the implant embedded in the premolar region was also seen in the design with the cantilever as compared to the conventional prosthesis design. DISCUSSION: The stress concentrations observed at the neck of the implant were similar to results reported in the literature. CONCLUSION: The highest stress value obtained in the study was 194.2 MPa with oblique loading. This value did not exceed the endurance limit of pure titanium, which is 259.9 MPa.

Cadaver↗

PubMed2006

How does canal taper affect root stresses?

AIM: To examine the effect of specific tapers on root stresses and thus vertical root fracture. METHODOLOGY: The effect of taper on root stresses was calculated during simulated warm vertical compaction of gutta-percha in a straight rooted premolar for three tapers (0.04, 0.06 and 0.12 mm mm(-1)) using finite element analysis. Stresses in the dentine were observed whilst the root was filled with three subsequent gutta-percha increments. Each increment was compacted at 10 or 15 N and the gutta-percha cooled down to 37 degrees C. After filling, composite was polymerized in the access space. A functional occlusal load of 50 N was then applied on the buccal cusp incline. The stress distribution in the root during the occlusal loading was compared with the stresses during filling. RESULTS: During filling, the highest stresses were found: (a) at the canal surface; (b) using the smallest taper; (c) in the apical third; and (d) during the first gutta-percha increment. The root stress distribution changed when the functional post-filling load was applied. It generated the highest stresses at the external root surface, with a tensile stress concentration at the lingual surface of the cervical third. Since the stresses during simulated masticatory loading concentrated on the external surface, an increased taper size caused only slightly higher root stress levels. CONCLUSIONS: With increasing taper, root stresses decreased during root filling but tended to increase for masticatory loading. Root fracture originating at the apical third is likely initiated during filling, whilst fracture originating in the cervical portion is likely caused by occlusal loads.

Computer Simulation↗

PubMed2004

Stress concentration in microtensile tests using uniform material.

PURPOSE: The objective of this study was to analyze the stress concentration factor (Kt) in specimens of uniform material with the most commonly used geometry (square hourglass) during microtensile tests using finite element analysis. Standardization is emphasized with the aim of obtaining the most representative nominal strength of the material. METHODS: Eighty cases were simulated using three-dimensional models, in which we varied the fixation of specimens in the jig (f = 1 or 2 sides), the height of this fixed region (h = 1 or 2.75 mm), the specimen width (D = 1.5, 2, 3, 4 or 5 mm), and the radius of curvature of the notch (r = 0.2, 0.5, 0.7 or 1 mm). The cross-sectional area (1 mm2) remained constant in all analyses. The stress concentration factor Kt (maximum tensile stress/nominal tensile stress) was calculated. RESULTS: A 150% difference was observed from the lowest Kt value (1.3) to the highest one (3.2). Results indicated that the radius of curvature is a very influential geometric parameter in microtensile strength tests (variation in Kt values up to 47.4%). For two-side fixed specimens, the Kt values varied from 3 to 4%, while the one-side fixed models resulted in variations from 11 to 15%. CONCLUSION: Variations in the specimen geometry and mode of load application can be responsible for part of the different strength values obtained in microtensile tests. The specimen fixation by two sides is a simple and easily performed method to reduce the stress concentration factor and its variations induced by specimen geometry and test assembly.

Acrylic Resins↗

PubMed2005

The influence of design parameters on the FEA-determined stress distribution in CAD-CAM produced all-ceramic dental crowns.

INTRODUCTION: Knowledge of factors, which influence stress and its distribution is of key importance to the successful production of durable all-ceramic restorations. The objective of this study was to evaluate, by finite element analysis (FEA), the influence of the shape of the preparation and the cement layer on the stress distribution in CAD-CAM produced all-ceramic crowns and in their cement layer. MATERIAL AND METHODS: The CAD models of multi-layer all-ceramic crowns for posterior tooth 46 of three patients produced with CAD-CAM-technology were translated into a three-dimensional FEA program. The stress distribution due to the combined influences of bite forces, residual stresses caused by the difference in expansion coefficient of the two ceramic layers, and the influence of shrinkage of the cement was investigated. RESULTS: The tensile stresses in the crown for the chamfer knife-edge preparation might put the integrity of the currently available ceramic materials at risk, while a non-uniform cement layer might result in stresses exceeding the bond strength. It was concluded that for long lasting restorations in the posterior region it is advisable to make a chamfer with collar preparation, the cement layer as uniform, and the difference in thermal expansion for the two ceramics as small as possible. SIGNIFICANCE: This study indicates that for full ceramic crowns in the posterior region, specific design rules should be followed, and that FEA utilizing CAD-CAM data can be a successful tool to develop design guidelines for all-ceramic restorations.

Bite Force↗

PubMed2000

Strain patterns in cervical enamel of teeth subjected to occlusal loading.

OBJECTIVES: This study was planned to investigate the variations in strains in enamel under different patterns of occlusal loading, using three-dimensional finite element analysis (3D FEA) and strain gage measurements in extracted teeth. METHODS: A 3D FEA model of a mandibular second premolar was used to investigate effects of occlusal load on enamel surface strains, particularly in response to oblique directions of cuspal loading. Point loads of 100 N were applied axially and at 45 degrees from the vertical on the buccal or lingual incline of the buccal cusp, either in the bucco-lingual plane or at varying mesio-distal angulations (up to +/- 20 degrees). Patterns of strain observed in the FEA model were confirmed experimentally using strain gages on extracted premolars mounted in a servohydraulic testing machine. RESULTS: Strains predicted from the FEA model were in excellent agreement with the strain gage measurements. Strains were concentrated near the cementoenamel junction (CEJ) regardless of load direction. A vertical load on the buccal cusp tip resulted in compressive strains on the buccal surface but small tensile strains in lingual cervical enamel. Strains resulting from oblique loads on buccal cusp inclines were complex and asymmetric, with either tension or compression occurring in any location depending on the site and angle of loading. SIGNIFICANCE: The magnitude, direction and character of strains in cervical enamel are highly dependent on patterns of loading. The asymmetric pattern of strains in buccal cervical enamel in response to oblique occlusal forces is consistent with the common clinical picture of asymmetric non-carious cervical lesions.

Analysis of Variance↗

PubMed2006

Buttressing angle of the double-plating fixation of a distal radius fracture: a finite element study.

Treatment of a distal radius fracture should consider principles including stable fixation and early motion. The aim of this study was to investigate the biomechanical interactions of plate-fixation angles in the internal double-plating method coupled with various load conditions using non-linear finite element analysis (FEA). A 3D finite element distal radius fracture model with three separation angles (50, 70, and 90 degrees ) between the buttressed L- and straight plates was generated based on computed tomography data. After model verification and validation, frictional (contact) elements were used to simulate the interface condition between the fixation plates and the bony surface. The stress/strain distributions and displacements at the radius end were observed under axial, bending, and torsion load conditions. The simulated results indicated that the bending and torsion increased the stress values more than the axial load. The radius and straight plate stress values decreased significantly with increasing fixation angles for all load conditions. However, the L-plate stress values increased slightly under the bending buckling effect. The displacements at the radius end and strains at the fracture healing interface decreased with increasing fixation angles for axial and torsion conditions but displayed a slight difference for the bending condition. The findings using FEA provide quantitative evidence to identify that much larger plate fixation angles could provide better mechanical strength to establish favorable stress-transmission and prevent distal fragment dislocation.

Biomechanical Phenomena↗

PubMed2002

Size and shape changes during late fetal growth (137-157 gestational days) in the pigtailed macaque (Macaca nemestrina) craniofacial complex: an application using three-dimensional coordinate data and finite element scaling analysis.

Form changes within the fetal pigtailed macaque (Macaca nemestrina) craniofacial complex was documented using finite element scaling analysis (FESA) and three-dimensional (3D) coordinate data for 35 craniofacial landmarks. Coordinate data were digitized from 3D reconstructions of computed tomography (CT) images and 2D axial slices. Twenty-two fetal pigtailed macaques ranging in age from 137 to 157 gestational days were included (in this species, birth is estimated at 170 gestational days). The null hypothesis that the craniofacial complex grows with isometry during late fetal growth of the craniofacial complex was tested (P < 0.05), and the prediction that morphological change along an anteroposterior axis dominates late fetal growth was also investigated. The null hypothesis was rejected, indicating that allometric growth is present during late fetal growth. Growth along an anteroposterior axis is localized in the palate and mandible. The neurocranium grows along a superoinferior axis, while the neurofacial junction displays growth along both the anteroposterior and superoinferior axes. Mediolateral changes are localized between asterions, the external auditory meati, and maxillary and mandibular alveolar points. Finally, a 3D model of craniofacial growth for this species was created, localizing size and shape changes that occur during late fetal growth for each of the 35 craniofacial landmarks defined in this study.

Animals↗

PubMed2004

Finite element growth analysis for the craniofacial skeleton in patients with cleft lip and palate.

The purpose of this study was to clarify the differences in the nature of craniofacial growth between subjects with normal occlusion and patients with unilateral cleft lip and palate (CLP) in terms of the size, shape and principal growth direction of craniofacial skeleton using finite element method (FEM). Lateral cephalograms were taken of 40 subjects as normal group and 178 patients as CLP group. These subjects were divided into seven developmental ages of 4-, 6-, 8-, 10-, 12-, 14- and 18-year-old. For the finite element analysis, the craniofacial complex was discretized into seven structures or elements with three nodal points in each after tracing each lateral cephalogram on acetate paper. For each stage, the growth parameters in CLP group were compared to those in normal group. The growth of upper facial skeleton and maxillary complex was more remarkably inhibited in CLP than in normal group. Especially, the growth inhibition of posterior maxillary complex in a vertical direction was remarkable in CLP group at any ages. Difference in the size and shape of entire mandibular skeleton between CLP and normal groups was not apparent. It is suggested that grow timing and peak velocity, an essential and key determinant to the success in orthodontic treatment, have been clarified in this study more clearly than in previous studies. It is hopefully anticipated to explore some key determinants to predict individual growth of the craniofacial skeleton near future.

Adolescent↗

PubMed2006

Finite element stress analysis of cuneiform and cylindrical threaded implant geometries.

Statement of problem. Different implant geometries present different biomechanical behaviors and in this context, one arising question is how cuneiform implant geometry compares to clinical successful cylindrical threaded implant geometry. Purpose. The purpose of this work was to study stress distribution around cuneiform and cylindrical threaded implant geometries using three-dimensional finite element stress analysis taking the latter as a reference. Material and methods. A model was generated from a computerized tomography of a human edentulous mandible with implants placed in the left first premolar region. The model was supported by the mastication muscles and by temporomandibular joint. A vertical load of 100N was applied at the top of each implant in the direction of their long axes. The mandibular boundary conditions were modeled considering the actual muscle supporting system. Taking muscle forces intensities and directions, balance moment equations were employed to assess the system equilibrium. Cortical and medullary bones were assumed to be homogeneous, isotropic and linearly elastic. Results. The analysis provided results for maximum (S1) and minimum (S2) principal stress and Von Mises (SEQV) stress field. For both geometries, the results showed concentration on one side of the neck, smooth stress distribution along the body and no considerable concentration at the apical area. Conclusion. Results showed similar stress distribution pattern for cuneiform and cylindrical threaded geometries. The stresses profiles along the implants length reproduced their morphology. In both occurred stress concentration at one side of the neck and no body or apical stress concentration.

Biomechanical Phenomena↗

PubMedDate not supplied

Comparison of non-linear finite element stress analysis with in vitro strain gauge measurements on a Morse taper implant.

PURPOSE: To understand the mechanical and biomechanical behavior of dental Implants, validation of stress and strain measurements is required. The objective of this study was to compare a non-linear finite element stress analysis with in vitro strain gauge measurements on strains in an implant-abutment complex. MATERIALS AND METHODS: Strain gauges were bonded to an Implant-abutment complex and embedded in polymethylmethacrylate resin. A force of 75 N was applied vertically and laterally in separate load cases, and strains were recorded with a strain indicator. Then, a finite element model of the strain gauge model was constructed. Contact analysis with normal contact detection and separation behavior was performed between the Implant and the abutment. The same loading protocol was followed, and strains were recorded at regions where gauges were bonded. RESULTS: Under vertical loading, the qualification and quantification of strains were similar in both methods. Under lateral loading, the measurement of strains on the abutment and in the resin were similar in both methods. However, strains on the implant collar as measured by non-linear finite element analysis were higher. DISCUSSION AND CONCLUSION: There is a compatibility between non-linear finite element stress analysis and in vitro strain gauge analysis on the measurement of strains under vertical loading. However, there are differences between the methods in the quantification of strains on the collar of Implants under lateral loading.

Acrylic Resins↗

PubMed2001

Evaluation of the effect of the residual bone angulation on implant-supported fixed prosthesis in mandibular posterior edentulism. Part II: 3-D finite element stress analysis.

Buccolingual angulation of the mandibular posterior edentulous region may affect the prosthetic load conditions, so as to cause high stress concentrated areas that may easily lead to failure. The aim of this study was to evaluate the effect of various predetermined buccolingual angulation values on stress distribution in the mandibular posterior edentulous region restored with implant-supported fixed partial dentures, using three-dimensional finite element analysis. Stress analyses were performed applying 400N oblique force to implant-supported fixed prosthesis. Stress analyses indicated tensile stress values on the buccal surface and compressive stress values on the lingual surface of cortical bone were increased as the angulation of the edentulous bone increased (especially corresponding to the cervical region of the implants). Compressive stress values, observed where two implants were placed at the second premolar and second molar regions (5-7 design) and first and second molar regions (6-7 design), respectively, were very close to or even exceeded the ultimate compressive strength of bone. It is concluded that when a definite buccolingual angulation is added to other existing risk factors such as bruxism, placing an implant for every missing tooth might reduce the high stress concentration areas.

Bicuspid↗

PubMed1985

Contact finite element stress analysis of the hip joint.

Two-dimensional finite element analyses were conducted of the normal hip using contact elements at the joint surface. The models studied were constructed for a slice through the pubis, acetabulum, and ilium. In the analyses the proximal femur was pressed into the acetabulum and intraarticular pressures and principal stresses in the joint region were determined for different load magnitudes and directions and various boundary conditions. Three sets of boundary conditions were examined: (a) deformable pubic symphysis, (b) rigid pubic symphysis, and (c) simulations of experimental studies. In the deformable model the pubic symphysis was free to displace in the sagittal plane and rotate. In the rigid model the pubic symphysis was rigidly fixed. Superoposterior loading resulted in high-contact pressures at the acetabular dome for all sets of boundary conditions. For the deformable model subject to a more medially directed load the acetabulum closed in such a manner as to squeeze the head of the femur creating high-contact pressures superiorly and inferiorly. This resulted in significant compressive stresses in the superior dome cancellous bone and inferior cancellous bone. The cumulative effect of this squeezing action with normal biological remodeling may cause elongation of the femoral head resulting in asphericity and incongruity of the unloaded hip joint articular surfaces. Rigidly fixing the pubic symphysis stiffened the model and resulted in principal stress patterns that did not reflect trabecular density or orientations as well as those of the deformable pubic symphysis model. Finite element simulations of previous experimental studies modeled the close proximity of the fixation to the excised acetabulum. These boundary conditions prevented the squeezing caused by pelvis deformations. The resulting contact areas, pressure distributions, and bone stresses were very different from those of the more anatomic, deformable pubic symphysis model. These findings demonstrate the sensitivity of hip contact pressures and stresses to imposed boundary conditions and indicate that care should be taken to simulate anatomic conditions in experimental and theoretical studies.

Acetabulum↗

PubMed1991

Three-dimensional finite element stress analysis in and around the Screw-Vent implant.

The three-dimensional finite element stress analysis method was used to determine the pattern and concentration of stresses within the Screw-Vent endosseous implant and its supporting tissues. For this commercially pure titanium implant, maximum stresses were located within the implant collar immediately below the bony crest. These stresses were at least 18 times less than the endurance limit of commercially pure titanium (259.90 MPa). Maximum stresses (19.57 MPa) in the bone were lingual to the superior portion of the collar. Previous longitudinal radiographic studies of a similar implant have revealed bone loss mesial and distal to the implant. For the Screw-Vent, mesial and distal stresses (maximum 0.38 MPa) were much lower than those buccal and lingual to the implant. The clinical significance of the stress transfer to the bone buccal and lingual to the implant has yet to be determined.

Alveolar Process↗

PubMed2004

Mechanical tests and finite element models for bone holding power of tibial locking screws.

OBJECTIVE: To investigate the bone holding power of tibial locking screws. DESIGN: The bone holding power was assessed by mechanical testing and finite element analysis. BACKGROUND: Screw loosening might threaten fracture fixation and bone healing. METHODS: In mechanical tests, six types of different tibial locking screws were inserted into low-density polyurethane foam tubes, which simulated osteoporotic bone. The screws were pushed out of the foam bone by an axial load, and the maximal pushout load was recorded. In finite element analysis, three-dimensional finite element models with a nonlinear contact interface between the screws and the bones were created to simulate the mechanical testing. The total strain energy of the bone and total reaction force of the screws were recorded. The contribution of the design factors was analyzed by the Taguchi method. RESULTS: In the mechanical tests, foam bone was stripped by the screw threads without screw deformation. The testing results were closely related to those of finite element analysis. The Taguchi analysis showed that the descending order of contribution of the design factors was outer diameter, pitch, half angle, and inner diameter. Root radius and thread width had minimal effects. CONCLUSIONS: The bone holding power of the screws could be reliably assessed by finite element models, which could analyze the effects of all the design factors independently and were potentially applicable to screws with irregular thread patterns.

Analysis of Variance↗