Porous structure design and mechanical behavior analysis based on TPMS for customized root analogue implant

Compared with the traditional dental implant with screw structure, the root analogue implant (RAI) is customized to fit with the wall of the alveolar bone, which helps to accelerate the clinical implantation process. However, a solid RAI made of Ti6Al4V material has a much higher Young's modulus than the surrounding bone tissue, which can cause a stress shielding effect and thereby lead to implant failure. Also, a solid RAI is not conducive to the growth of osteoblasts. To overcome these problems, a porous structure design and optimization method for customized RAIs is proposed. A triply periodic minimal surface (TPMS) offers a smooth surface with pore interconnectivity, which can satisfy the biological/mechanical implantation requirements and efficiently construct many complex bone scaffolds. P and G structures with four degrees of porosity (30%, 40%, 50%, and 60%) were designed and prepared as cubic samples. The Young's modulus, Poisson's ratio, and yield strength of each sample were measured through compression experiments. Additionally, the stress distribution at the interface between the customized RAI and surrounding bone tissue under different pore structures and porosities was evaluated by finite element analysis (FEA). It was found that the quantitative relationships between the Young's modulus/Poisson's ratio and porosity of the P and G structures were consistent with the rules of the percolation model. The yield strengths of the P and G structures with four different porosities were all greater than the yield strength of cortical bone, which satisfies the implantation conditions. Furthermore, the P and G structures with 30% and 40% porosity were proved by FEA to have no stress shielding effect, promote the growth of surrounding bone tissue, and form long-term and stable osseointegration. It can be concluded that the porous RAI constructed with a TPMS can reduce the stress shielding effect, which is beneficial for accelerating the clinical implantation process.