Within the limits of this study, the results suggest that the use of dowels and cements with mechanical properties similar to those of dentin, and an increased cement layer thickness, results in mechanical behavior similar to the physiological behavior of a sound tooth.

The focus of this paper is to establish a characterisation method for seven polyamide (PA) grades to determine the major material to manufacture an automotive worm gear. The composite properties were measured according to the worm gear loadings: tensile strength, Young's modulus, abrasion and impact resistance. They were also correlated to the PA moisture absorption and its glass fibre (GF) reinforcement. The data from mechanical tests were applied in the finite element analysis (FEA) using the von Mises stress criterion. Before the rig tests of the PA worm gears, the injection process was evaluated, through the capillary rheometry. A higher difficulty to process PA 6/6 30% GF was found, due to its lower apparent viscosity. In the end, the influence of moisture absorption was as decisive to the gear's material selection as the GF to the pinion. Thus, the PAs with the best performance were: PA 6 with 30% GF (gear) and with PA 60% GF (pinion).

T he objective of this research was to evaluate, by three-dimensional (3D) finite element analysis (FEA), the stress distribution in three different fiveimplant mandibular protocol prosthesis models, when these three undergo a simulated occlusal load of 100 N in the area of the cantilever: (1) model A, temporary all-acrylic resin; (2) model B, metal-acrylic; and (3) model C, metal-ceramic. Materials and Methods Modeling of the External and Internal Portions of the MandibleThe external 3D modeling of the mandible was acquired from the laser digitization of a natural edentulous mandible in the sagittal, horizontal, and frontal planes (0.01mm precision) using Digimil 3D (Technodrill). The first 3D model was created using Geomatic Studio version 7.0, and then a continuous model was obtained using Rhynoceros 3D version 3.0.A tomographic image (70 transversal vertical slices, 1-mm thickness) of the same edentulous mandible was obtained using Helicoidal Tomographic Hispeed CTI System Series 6.3 (GE Healthcare). This image was superimposed over the external mandible model to develop the internal model (Rhynoceros 3D version 3.0). Modeling of Implants and Prosthetic ComponentsThe 3D shapes of implant and prosthetic components were obtained by manual measurements (eg, length, diameter, thread pitch) with magnifying lens and a digital caliper. These dimensions were used for generating digital surfaces (Rhynoceros 3D version 3.0), and then solid shapes were obtained (SolidWorks 2012, SolidWorks).

In real-world structural problems, a number of factors may cause geometric imperfections, load variability, or even uncertainties in material properties. Therefore, a deterministic optimization procedure may fail to account such uncertainties present in the actual system leading to optimum designs that are not reliable; the designed system may show excessive safety or sometimes not sufficient reliability to carry applied load due to uncertainties. In this paper, we introduce a hybrid reliability-based design optimization (RBDO) algorithm based on the genetic operations of Genetic Algorithm, the position and velocity update of the Particle Swarm Algorithm (for global exploration), and the sequential quadratic programming, for local search. The First-Order Reliability Method is used to account uncertainty in design and parameter variables and to evaluate the associated reliability. The hybrid method is analyzed based on RBDO benchmark examples that range from simple to complex truss parametric sizing optimizations with stress, displacements, and frequency deterministic and probabilistic constraints. The proposed final problem, which cannot be handled by single loop RBDO algorithms, highlights the importance of the proposed approach in cases where the discrete design variables are also random variables.

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Purpose: This 3D-finite elements method study evaluated the effect of bone resorption on the stress distribution in overdentures with bone loss surrounding implants and resorption of the distal ridge. Methods: Tridimensional models were built from the images of a computerized tomography of a mandible and 3D laser digitalization of implants, abutments, mucosa, and complete denture. The geometric models of implants and abutments were mounted at the canine region to build reference model 1-absence of bone resorption. To build the test models the mandible geometric solid was modified to simulate 2-mm vertical bone loss surrounding the implants (model 2) and resorption of the distal ridge (model 3). Finite elements models were generated, and a 100 N static load was applied at the first molar region of each model to compare the von Mises stress distributions in selected points. Results: Von Mises stresses increased on the bone surrounding implants and on the prosthetic components in the model with 2-mm vertical bone loss. The combination of 2-mm vertical bone loss and resorption of the distal ridge did not increase the stresses compared with the model with only bone loss surrounding implants. The highest stress concentration at marginal bone and implants occurred on the same side of the vertical load application for all models. Conclusion: The results suggest that the bone loss surrounding implants increases stress concentration in dental implants, abutments, and marginal bone independently from the bone resorption of the distal ridge.

This paper evaluates the mechanical behavior of an uncemented hip stem using finite element analysis.The analysis is focused on the stem-bone interaction which is assessed by simulation of distinct conditions encountered daily on orthopedic practice of hip implants. Logical uncemented femoral stem was used in this work. Three distinct conditions have been modeled: a) exposed neck with fully embedded fins, b) partially exposed anti-rotational fins and c) fully exposed fins, representing real femoral hip conditions. Anthropometric variations and different angulations for the stem neck were investigated for typical body weight of populations submitted to implants. The ratio of mobilized stress to yield stress is shown to be lower than 55% indicating a safety factor against stem failure. Although small displacements are observed in all conditions, the displacement increases with the increase of both the length of exposed fins and the magnitude of applied forces. Even for the extreme condition of fully exposed fins, the prostheses will support the working loads, and the risk of bone fracture still has a safety factor. Stresses and displacements change considerably with neck angulations suggesting that anthropometric variations should be considered in the future to optimize prostheses performance. Numerical analysis of the used uncemented femoral stem demonstrated that small stresses and strains are generated under working load conditions indicating that a proper factor of safety is obtained for the static conditions tested in the present study.Keywords Numerical analysis, Hip surgery, Uncemented stem, Prosthesis. Análise numérica do comportamento biomecânico da haste femoral não-cimentada Logical