Inelastic behaviour of bone tissue in interaction processes with dental implants

Dental implantology is commonly adopted for the treatment of edentulous patients. The reliability is mainly determined by interaction phenomena between implant and bone tissue, that are affected by loading imposed and the corresponding response of bone tissue. Dental implants biomechanics can be investigated by numerical methods. An accurate characterization of bone mechanical response by specific constitutive formulations is required. Elastic orthotropic model is adopted with regard to the elastic phase of the material, accounting for non-homogeneous distribution of mechanical properties. At this purpose, a procedure is developed to provide a distribution of orthotropic elastic properties over the anatomical region where the implant is placed. Furthermore, attention must be focused on problems that are part of clinical practice and can determine relevant strain/stress, imposing the consideration of bone inelastic response. In particular, misfit and press fit conditions are investigated. Misfit occurs in multiple implant frames, when no perfect geometric compatibility occurs between connecting framework and implants. Press fit is due to the fact that the diameter of hole drilled within the mandible is smaller than the implant one. Both these phenomena determine a post elastic deformation of bone tissue and entail the assumption of a visco-elasto-plastic constitutive model capable of an appropriate interpretation of the response. Numerical models of mandible and implant systems are provided to analyse misfit and press fit. The analyses developed allow for an interpretation of the effects of the surgical procedures in terms of stresses and strains in the peri-implant tissues and represent the basis for implant reliability and durability evaluation.