Performance evaluation of dental implants: An experimental and numerical simulation study

Dental implants are widely used in replacing missing teeth. However, some problems may occur such as screw loosening or screw fracture which lead to implant failure. In this regard, it is of utmost importance to analyse some of the factors that affect the primary stability and consequently the osseointegration of dental systems. In the present study, particular attention is given to the bone density and the bone-implant contact in order to evaluate the implant performance. Given the difficulty in working with bone in vivo, in the present study two implant systems were inserted in polymeric samples, of different densities, known as Sawbones, which simulate the structure of trabecular bone. The implant systems chosen were external hexagon and Morse taper. The performance of the implants was evaluated through experimental fatigue tests that simulate the chewing or mastication cycles. The qualitative analysis of the damage in the cellular structure of the samples was performed using scanning electron microscopy (SEM). The finite element (FE) method was used to model the penetration of the implants and enable the determination of the stress at the implant and deformations at the Sawbones-implant vicinity. Prior to penetration simulations, a well-known analytical model of indentation was compared with indentation simulations, in order to validate the numerical model. The major difference between numerical and analytical model results, in the case of the displacements, was found to be around 9%. The failure of the Sawbones occurred with the propagation of the collapsed cells according to SEM observations. The fatigue results showed that the Morse taper implant exhibited lower displacements than the external hexagon. Higher density Sawbones also exhibits lower deformations, while keeping the other parameters constant. It means that Morse taper and high dense materials show a better fatigue performance than the other systems and materials. The FE results for penetration showed that a threaded geometry implant when compared to smooth geometry provided a reduction of the stresses in the implant and reduces the deformations in the Sawbones. The results of the penetration simulations follow the same trend as the indentation simulations and analytical model. Simulation results show that the displacements are reduced with the increase of the density of the polymer foam. This is in agreement with the fatigue results. Comparing bones with foams, it could be concluded that, the increase of the bone density will induce a higher stability of the implants.