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At least 937 records · Page 52Linked to original sources
PubMed2001

Nonlinear model of skin mechanical behaviour analysis with finite element method.

BACKGROUND/AIMS: A problem commonly encountered in plastic and reconstructive surgery is the prediction of the stress put on the skin when various types of skin flaps are used. METHODS/RESULTS: We developed a mathematical model based on the finite element method, in order to determine the stress field, by simulating the mechanical behaviour of human skin during wound closure. We chose to take into account the low compressive strength by modifying the mechanical parameters of the model at each step of the calculation. The model has been developed and tested on a diamond-shaped incision and applied on a Limberg incision. CONCLUSION: The results presented are the Von Mises stress in the area of skin around the scar and, when possible, the resultant closure force. They show the relevance of the method.

Biomechanical Phenomena↗
PubMed1995

A three-dimensional finite element stress analysis of angled abutments for an implant placed in the anterior maxilla.

PURPOSE: A three-dimensional mathematical model of the maxilla was developed that was used to analyze the stresses and strains produced by an abutment system capable of three abutment angulations. MATERIALS AND METHODS: Computed tomography was used to derive the geometry and density values used for the maxillary model. A 3.8 x 10-mm cylindrical implant was embedded in the right central incisor position at a 35 degrees angle to the horizontal plane and parallel to the angulation of the bone site. All geometric and elastic properties for the fixture and the surrounding bone were included in the model. A simulated occlusal load of 178 N was applied along the long axis of 0 degrees, 15 degrees, and 20 degrees abutments. The mathematical models were solved by the Cray Y/MP Ohio Supercomputer (Cray, Eagan, MN) using the ABAQUS software program (Hibbitt, Karlsson, and Sorenson, Providence, RI). RESULTS: Numerical and graphic results were generated for the maximum (tensile) and minimum (compressive) stresses and strains. Principal stresses occurred predominantly in the cortical bone layers, whereas strains occurred mostly in the cancellous bone. CONCLUSIONS: In general, there was an increase in the magnitude of stress and strain as the abutment angulation increased. Reported stresses and strains for all three angles were within or slightly above the physiological zone derived from animal studies. A need to investigate the response of human bone to stress and strain was indicated.

Alveolar Process↗
PubMed1992

Finite element stress analysis of a push-out test. Part II: Free interface with nonlinear friction properties.

In this second part of a two-part paper, nonlinear frictional properties measured at the bone/porous-surfaced metal interface are used to perform the stress analysis of a push-out test assuming free interface. In this case, the friction at the interface is the only mechanism to resist the externally applied load. Similar to the part I, the model is axisymmetric and consists of two cylinders in contact with each other through the interface. Various relative material properties and boundary conditions are simulated in order to examine their effects on the interface stresses and overall push-out resistance. The role of the force-fit and the load direction (push-out versus pull-out) on the results is also investigated. The computed radial and shear stresses are found to markedly vary both with location along the interface and with the testing configuration. The ultimate push-out resistance is also found to significantly alter as the material arrangement and boundary conditions change. The predicted push-out load augments with an increase in the force-fit and diminishes to nil in the absence of a press-fit. For the cases studied here, there is a relative difference of as large as 13 percent between the push-out response and the pull-out response so far as the interface stresses and the maximum resistance are concerned. Therefore, any comparison between the results of push-out (or pull-out) tests performed with different design configurations appears to be invalid.

Biomechanical Phenomena↗
PubMed2005

Analysis of finite element models for head injury investigation: reconstruction of four real-world impacts.

Previous studies have shown that both excessive linear and rotational accelerations are the cause of head injuries. Although the head injury criterion has been beneficial as an indicator of head injury risk, it only considers linear acceleration, so there is a need to consider both types of motion in future safety standards. Advanced models of the head/brain complex have recently been developed to gain a better understanding of head injury biomechanics. While these models have been verified against laboratory experimental data, there is a lack of suitable real-world data available for validation. Hence, using two computer models of the head/brain, the objective of the current study was to reconstruct four real-world crashes with known head injury outcomes in a full-vehicle crash laboratory, simulate head/brain responses using kinematics obtained during these reconstructions, and to compare the results predicted by the models against the actual injuries sustained by the occupant. Cases where the occupant sustained no head injuries (AIS 0) and head injuries of severity AIS 4, AIS 5, and multiple head injuries were selected. Data collected from a 9-accelerometer skull were input into the Wayne State University Head Injury Model (WSUHIM) and the NHTSA Simulated Injury Monitor (SIMon). The results demonstrated that both models were able to predict varying injury severities consistent with the difference in AIS injury levels in the real-world cases. The WSUHIM predicted a slightly higher injury threshold than the SIMon, probably due to the finer mesh and different software used for the simulations, and could also determine regions of the brain which had been injured. With further validation, finite element models can be used to establish an injury criterion for each type of brain injury in the future.

Journal Article↗
PubMed2006

Stress analysis of endodontically treated anterior teeth restored with different types of post material.

Finite element analysis was performed to evaluate stress distribution in maxillary central incisors treated endodontically and restored with a post and an all-ceramic crown. Tensile stress at tooth root was analyzed using two-dimensional finite element models with different post diameters and lengths. One post length was 1/3 of the root (short), while the other was 2/3 of the root (long); one post diameter was 1/3 of the root (narrow), while the other was 2/3 of the root (wide). The following combinations were used for posts and cores: gold alloy cast post and core, commercial stainless steel post and resin core, and fiber post and resin core. Results showed that the fiber post produced less stress on the root dentin around the post tip than did the metal posts. This finding thus suggested that to reduce the stresses that cause root fracture, a long, thin fiber post should be used.

Dental Stress Analysis↗
PubMed2004

Effect of metal strengthener length on stress distribution in acrylic denture bases: a finite element study.

This study investigated the influence of metal strengthener length on stress created in acrylic denture bases in relation to location of the vertical support to the dentures. Finite element analysis was conducted to calculate stress generated in the straps of 2 mm-thickness and 18 mm-width that were reinforced with metal strengtheners of five different lengths. A vertical biting force of 60 N was directed on one end of each strap, while the other end was fixed. Vertical movements were restricted at one of the three support locations between the centre of the strap and the loading site. When the straps were vertically supported near the loading site, greater maximum tensile stresses were seen in the straps with relatively short strengtheners than those shown in the straps with longer strengtheners. The metal strengtheners with sufficient length may provide a preventive denture design against the acrylic fractures.

Acrylic Resins↗
PubMed2002

Tooth-implant connection: some biomechanical aspects based on finite element analyses.

This study investigated, with the use of two- and three-dimensional finite element analysis, the peri-implant stress that occurred during loading of a tooth that was rigidly connected to a distally placed implant. A fixed bond between the bone and the implant was assumed, while the periodontal ligament was represented by means of three-dimensional nonlinear visco-elastic spring elements. Two different loading conditions were compared in the study: i) an axially directed static load of 50 kg that was applied to the tooth for 10 s, and ii) a transitional load of 50 kg that was applied for 5 milliseconds. Load duration appeared to have a greater influence than load intensity on the stress distribution in the bone around an implant and a rigidly connected tooth. Static load is, therefore, potentially more harmful for peri-implant bone than transitional load. The periodontal ligament seems to play a key role in the stress distribution between a tooth and a rigidly connected implant.

Alveolar Process↗
PubMed2005

Three-dimensional analysis of electrode behavior in a human cochlear model.

Three-dimensional (3D) finite element analysis is used in this study to model the mechanical effects of the electrode in a cochlear implant. We employ six electrodes with different stiffness produced by different arrangements of metal wires. Different wire arrangements are generated by changing the fitness function of a genetic program. The human cochlea is modeled by the spiral-approximation method. Reconstructed three-dimensional CT images are used to model the real insertion condition. The contact pressure at the tip and the insertion force are found to be highest when the wires are stacked horizontally. Axial rotation of the electrode has minimal effect on the stimulating current spread. The electrode does not contact the basilar membrane. The results indicate that considering the electrode stiffness is important to minimizing mechanical trauma in cochlear implantation.

Acoustic Stimulation↗
PubMed1998

The influence of cross-sectional shape and surface area on the microtensile bond test.

OBJECTIVES: The purpose of this study was to determine the effect of the cross-sectional area shape (cylindrical vs. rectangular) and the bonding surface area on the microtensile bond strengths and stress distribution of four dentin adhesive systems (Scotchbond MP Plus, OptiBond FL, OptiBond Solo, One-Step). In addition, finite element analysis (FEA) models were developed to investigate stress distributions. METHODS: Extracted human molars were cut vertically and the occlusal enamel removed; one-half of the tooth was used for rectangular specimens, the other half for cylindrical specimens. The occlusal dentin was bonded according to the manufacturers' directions and covered with a block of resin composite. For the cylindrical specimens, the bonded dentin was shaped with a diamond bur on a lathe to produce specimens of area 1.1, 1.5 or 3.1 mm2 at the bonded interface. The rectangular specimens were sectioned to obtain bar-shaped specimens, which were shaped to produce hour-glass shaped specimens with the same area as the round specimens. Bonds were stressed in tension at a speed of 1 mm min-1. The mean bond strengths were compared using two-way ANOVA, one-way ANOVA, LSD and Student's t tests. The fractured surfaces were examined by scanning electron microscopy, and the frequencies of the fracture modes were compared using the Kruskal-Wallis and Mann-Whitney U tests. FEA models were created simulating the cross-sectional areas for bonding to determine the stress distribution. RESULTS: The 3.1 mm2 bonding area groups showed significantly lower bond strengths than the 1.1 mm2 bonding area groups (p < 0.05), except for the rectangular specimens using Scotchbond MP Plus and One-Step. Most cylindrical specimens of bonding area 1.1 or 1.5 mm2 exhibited adhesive failure at the interface between the dentin and the adhesive resin. No differences were determined between cylindrical and rectangular specimens. The fracture mode matched the stress distribution patterns calculated from the FEA modeling. SIGNIFICANCE: The results indicate that the test methods using small surface areas produce higher bond strengths than those using larger surface areas, and that cross-sectional shape has little effect. This is probably a result of fewer defects occurring in the small-area specimens.

Analysis of Variance↗