Finite Element Combined Design and Material Optimization Addressing the Wear in Removable Implant Prosthodontics

Wear at the male-female interface of retentive elements in implant-supported removable prostheses is the most frequent complication in such applications. The lack of an ideal/optimal insertion path, as well as the fabrication inaccuracies, are the primary contributors to this issue. A male attachment with a common ball anchor enhanced by lateral flexibility was investigated as a solution, compared to the widely used rigid ball anchor design. A parametric finite element analysis was performed to compare the wear-inducing maximum strain at the female polymer counterpart by various attachment designs made from titanium and Nitinol. The evolution of mechanical strains causing wear in the female part, as well as the contribution of stresses and martensitic transformation in the implant's flexible shaft, were evaluated under several insertion misfit scenarios. Results indicate that introducing a long flexible shaft in the titanium implant reduced maximum strains in the female attachment part by up to 61% as compared to the solid ball anchor. Further improvement was observed by using the shape memory alloy Nitinol as shaft material, leading to a minor reduction in stress and strain at the contact surface but allowing for a shorter abutment. Finally, the optimized Nitinol implant design with a short, necked flexible shaft promoting martensitic transformation at low plateau stress resulted in an approximate 90% reduction in maximum strains at the inner surface of the female part during manual insertion, which indicates a significantly reduced wear phenomenon at the contact.