A micromechanical multiscale model which estimates the elastic properties of cortical bone as a function of porosity and mineral content is presented. The steps of the model are divided into two main phases. In the first one, the elastic properties of the collagen fibril, collagen fiber and lamella are given. In the second phase, porosity is included in the lamella in the form of canaliculi, lacunae and Haversian canals, to provide the elastic properties of the osteonal tissue. Then, a symmetrization technique is used to estimate the transversely isotropic elasticity tensor of the osteon. Osteons are superimposed using a self-consistent scheme, and finally, the fluid filling the pores is included to estimate the elastic constants of the undrained cortical tissue. The main novelty of the model presented here is the possibility of varying the mineral content of bone, considering that mineralization begins from the inner levels, initially intrafibrillar and then interfibrillar. Correlations of the elastic properties of cortical bone obtained with this model on the one hand, and porosity and ash fraction on the other hand, are estimated.

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A finite element model of the temporomandibular joint (TMJ) and the human mandible was fabricated to study the effect of abnormal loading, such as awake and asleep bruxism, on the articular disc. A quasilinear viscoelastic model was used to simulate the behaviour of the disc. The viscoelastic nature of this tissue is shown to be an important factor when sustained (awake bruxism) or cyclic loading (sleep bruxism) is simulated. From the comparison of the two types of bruxism, it was seen that sustained clenching is the most detrimental activity for the TMJ disc, producing an overload that could lead to severe damage of this tissue.

Bone is able to adapt itself to the mechanical and biological environment by changing its porosity and/or orientation of its internal microstructure in a process known as bone remodelling. As a consequence, a change of bone mechanical properties is produced leading to an optimum structure, able to bear the external loads with the minimum weight. This adaptation is carried out by a temporal association of cells known as BMUs (basic multicellular units) that resorb old bone and sometimes produce new organic extracellular matrix (osteoid) that is later mineralized. This involves changes in porosity, damage level (density of microcracks accumulated by cyclic loads) and mineral content. All of these features were taken into account in a previous model, but the whole process and therefore the resulting bone constitutive behaviour was considered isotropic. The model proposed herein, recognizing that bone is actually anisotropic, tries to explain how BMUs modify the anisotropy by changing their progressing direction. We check the potential of the model to predict the alignment of the bone microstructure with the external loads in different situations. Then, the model is also applied to obtain the anisotropy and mechanical properties of the human proximal femur under physiological loads with initial conditions corresponding to a heterogeneous, but otherwise isotropic bone.

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