Identifying Elastic Constants for PPS Technical Material When Designing and Printing Parts Using FDM Technology.

This paper introduces a methodology to study the anisotropic elastic constants of technical phenylene polysulfide thermoplastic (PPS), printed using fused deposition modeling (FDM) in order to provide designers with a guide to achieve the required mechanical properties in a printed part. The properties given by the manufacturer are usually taken from injected samples and these are not the real properties for printed parts. Compared to other plastic materials, PPS offers higher mechanical and thermal resistance, lower moisture absorption, higher dimensional stability, is highly resistant to chemical attacks and environmental aging, and its fireproof performance is good. One of the main difficulties presented when calculating and designing for FDM printing is that printed parts present anisotropic behavior i.e., they do not have the same properties in different directions. Haltera-type samples were printed in the three manufacturing directions according to optimum parameters for material printing, aimed at calculating the anisotropic matrix of the material. The samples were tested in order to meet standards and values for elastic modulus, shear modulus and tensile strength were obtained, using Digital Image Correlation System to measure the deformations. An approximated transversally isotropic matrix was defined using the obtained values. The fracture was analyzed using SEM microscopy to check whether the piece was printed correctly. Finally, the obtained matrix was validated by a flexural test and a finite element simulation.

Dental implants with conical implant-abutment interface: influence of the conical angle difference on the mechanical behavior of the implant.

PURPOSE: Misfit in the conical implant-abutment interface plays an important role on the mechanical behavior of the implant when masticatory forces are applied. The origin of the misfit adopted in this work is a conical angle difference between implant and abutment, which can be due to a combination of design decisions and manufacturing tolerances. The goal of this work was to investigate the effects of the implant-abutment conical angle difference in the following mechanical features: interfacial microgap, preload loss on the bolt, stress level in the bone, and abutment removal force and/or torque. MATERIALS AND METHODS: A simplified three-dimensional nonlinear monoparametric finite element model of an OsseoSpeed TX 4.5 S 9-mm implant (Astra Tech) with a tapered implant-abutment interface was built to evaluate the variability of the mechanical features cited above with the conical angle difference, keeping constant the overall geometry, load and boundary conditions, material properties, frictional behavior, and mesh structure. RESULTS: As the conical angle difference increased, the following effects were observed: the microgap decreased and remained almost constant for values over a given positive angle difference, the stress level in the bone increased sensitively, the removal force and/or torque needed to separate the abutment from the implant varied slightly, and the bolt preload loss increased. CONCLUSIONS: In light of the results provided, the conical angle difference in the implant-abutment interface had a significant influence on the overall mechanical behavior of the implant. Among the four mechanical features considered, the interfacial microgap and the bone stress were demonstrated to be the most sensitive to the conical angle difference, and therefore the most relevant when selecting an optimum value in the design process of a conical interface.