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Vol 4 - Issue 2

Uncertainties and Reliability of Multiphysical Systems

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A significant effect of bone anisotropy on reliability measurements of mini-plate fixation system used in multiple mandibular fractures: A clinical case of angular and parasymphysis fractures

Mechanical properties of bone tissues are very important when introducing fixed mini-plates into multiple fracture cases. The effect of these properties becomes more significant when dealing with reliability analysis where several failure modes can occur. In our previous work, the anisotropy case considering a single fracture case and a single failure mode, led to a low reliability index value during the convalescence period. In this work, the studied clinical case contains two different fractures that certainly leads to a very low reliability index value. This makes no sense to assess the reliability level at the convalescence period. Thus, the anisotropy effect is studied at the end of the healing period where the fracture surfaces must be bonded. Two material models are elaborated for the studied clinical case (a male patient at the age of 35 years) where two different fractures exist. In Study I, isotropic bone tissues are considered, while in Study II, anisotropic (orthotropic) bone tissues are considered. A successful healing requires that a number of constraints which are affected by the loading conditions are fulfilled, and since muscle activity is difficult to estimate, there is a strong need to introduce the uncertainty on the loading in order to obtain a reliable design. The failure mode occurs when the yield stress of one or more parts is reached. The results show that when performing a direct simulation, there is a significant difference of maximum von-Mises stresses in the cancellous bone tissues between the isotropy and anisotropy cases. In addition, the failure modes and the reliability indices are very affected when considering the bone anisotropy. It is recommended to consider bone anisotropy in order to obtain more realistic results.

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