Through a process called osseointegration, a compact bone tissue is formed around the dental implant during healing after the surgery. Although this process is known for almost 40 years, the exact mechanical behavior of the newly grown bone around the implant remains badly understood. Microscopic observations have highlighted the presence of osteons at the interface with the implant. Osteons are cylindrical structures composed of soft collagen proteins and rigid mineralized bone apatite. Understanding the mechanical behavior of this microstructure could be a key to understand the purpose of its formation in bone, and thus, to achieve desirable osseointegration and modification of the bone composition. This study aims at developing a numerical method using finite element method (FEM) to obtain microscopic strain in an osteon in the peri-implant lower jaw bone under macroscopic chewing-like loading condition applied to the dental implant. To consider the macroscopic load, micro-CT images were used together with Second Harmonic Generation (SHG) images to model the collagen proteins in an osteon.

The resolution of the Micro-CT images is 90×90×50𝜇m and the resolution of the SHG images is 0.83×0.83×20𝜇m. A zooming FEM was used to cope with the difficulty of a huge scale gap between macro- and microscopic models. In order to reduce the scale ratio between two finite element models, a mesoscopic model is also created from Micro-CT images. The position and orientation of the SHG image-based microscopic model were carefully set in the micro-CT image-based macroscopic model. As the model is linear elastic, the displacement and strain under arbitrary loading condition were calculated by only three analyses under axial loading cases. For this analysis, a python code and image-based FEM software VOXELCON (Quint Corp, Tokyo, Japan) were used.

From the cartography of the principal strain obtained over a wide scattering of loading directions, three loading cases where chosen to be further discussed. A higher strain was observed under shear displacements than under compression. The strain was mainly located in the fiber-rich areas. The fiber parts of the osteon tends to act like a cushion to absorb deformations around the blood vessel.