The stiffness and strength properties of foams with tetrakaidecahedral unit cells are evaluated using both finite element-based micromechanics and analytical methods. The finite element analysis models the varying cross section of the struts exactly. The analytical methods assume the struts have constant cross section along the length. Equivalent constant cross section of the strut can be obtained by either matching the densities or by using harmonic averaging of the stiffness properties. A method in which the moment of inertia of the cross section is averaged is also considered. The comparison of properties obtained for the different equivalent constant cross-section foams shows the inability of the various averaging schemes to match the shear modulus and the strength properties, while the Young’s modulus matches to some extent. The failure of the weakest cross section in the varying cross-section strut of the unit cell leads to a lower tensile strength in the actual foam compared to the uniform cross-section foams. The results suggest that although the use of simple analytical models for foam properties are attractive, they often lead to erroneous results, and hence exact modeling of the strut geometry is key to estimating the stiffness and strength properties of foams and other cellular solids.
Purpose: The aim of this study was to determine stress levels on supporting structures of implant-retained overdentures as a function of varying degrees of palatal coverage using finite element analysis modeling at different loading angles. Materials and Methods: ABAQUS®-software was used to perform finite element analysis on eight overdenture models with three and four implants and with and without palatal coverage designs. Loads were applied perpendicular and 45º to the implants. Von Mises stress was measured to determine bone stress. A one-way ANOVA determined which model caused the most stress to the maxillary bone. Results: Palatal coverage increased stress to anterior implant in three implant (p = 0.08) models but decreased stress to all implants in four implant models (p = 0.43). Distal implants received more stress than anterior implants for all models. There was no significant difference between a full palate and no palate coverage overdenture prosthesis when a bar was added under axial loading (p = 0.954). Under non-axial loading, a decrease in stress was noted with the bar in all areas except the anterior implant site. Conclusions: Palatal coverage may not be necessary when applying a pure axial load. The addition of a bar decreased stress at loading.
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