MECHANICAL BEHAVIOR ANALYSIS OF A FUNCTIONALLY GRADED POROUS DENTAL IMPLANT

Medically compromised patients causing severe amounts of bone loss in the maxillary/mandibula experience low success rates with dental implants. The bone loss is caused by a weak interfacial connection between the implant and the maxillary/mandibula and because of a stiffness mismatch between bone and titanium. To address this challenge, functionally graded porous dental implants are proposed as a promising solution to mimic the natural tooth by matching the stiffness of the titanium support with the maxillary/mandibula. In this paper, we employed functionally graded materials to design a triply periodic minimal surface (TPMS) gyroid-graded porous structure with five distinct connected porosities leading to a solid core. The study aimed to develop a structure with mechanical properties similar to bone while maintaining mechanical strength to withstand physiological loading. An analytical model for a functionally graded porous structure was utilized to calculate a theoretical elastic modulus in relation to five different porosities along the gradient. The target porosities were determined as 10%, 20%, 30%, 40%, and 50%, with corresponding elastic modulus ranging from 103.94 GPa to 35.25 GPa. Five TPMS solid gyroid samples made of Ti-6Al-4V were designed for a specific stiffness corresponding to the bone, using an analytical model considering an exponential relationship between stiffness and porosity. These structures were then manufactured through selective laser melting, resulting in final porosities of 6.64%, 11.56%, 18.40%, 28.74%, and 36.23%, with corresponding pore sizes of 130 µm, 185 µm, 280 µm, 360 µm, and 420 µm. The stiffness of the designed and manufactured porous structures was validated through uniaxial compressive experiments. Digital Image Correlation (DIC) accurately recorded displacements to calculate strain during compression experiments up to failure. Microscopic analysis of the compression samples' failure provided insights into the role of pores in sample damage. Results confirmed that the elastic modulus of the porous structures was reduced to the designed values between 21.7-65.3 GPa, compatible with bone. This represents a significant drop in stiffness compared to solid Ti-6Al-4V, for which stiffness is 114 GPa. Through this matching of stiffness between bone and the implant, the so-called stress shielding effect caused by a weak interfacial connection can be reduced, decreasing the risk of implant failure.