The effect of implant thread design on stress distribution in anisotropic bone with different osseointegration conditions: a finite element analysis

Abstract

Purpose: Whereas bone is anisotropic, nearly all previous mechanical analyses of implants assumed bone as an isotropic material. Another means to simplify a simulation of the biomechanics of the implant-bone interface is the assumption of complete or no osseointegration; in clinical reality, an implant never achieves 100% contact with the surrounding bone. This study evaluated different thread profiles while not taking into account these two common simplifications. This study sought to (1) investigate the effects of various implant thread designs on stress distribution in the peri-implant bone, (2) appraise previous efforts in this area, and (3) find an optimum basic thread-form design.

Materials and methods: Through finite element analysis, four different basic commercial thread-form configurations for a solid screw-type implant were modeled: buttress, reverse buttress, V, and square. Bone was assumed to be transversely isotropic, and various degrees of osseointegration were simulated.

Results: Simulations showed that von Mises stresses were more distributed in the mesiodistal direction. Additionally, maximum stresses were concentrated at the cervical cortical bone region and the first thread. Moreover, in most of the models, von Mises stresses gradually increased in the supporting structure when the degree of osseointegration increased.

Conclusion: The use of different thread designs and various osseointegration conditions did not affect the stress distribution patterns in the supporting bone. In this study, square threads showed the most favorable results according to the predicted values of von Mises equivalent stress, pressure, different shear stresses, and micromotion.