Biomechanical comparison of implant inclinations and load times with the all-on-4 treatment concept: a three-dimensional finite element analysis

The purpose of this study was to compare the effects of implant inclinations and load times on stress distributions in the peri-implant bone based on immediate- and delayed-loading models. Four 3D FEA models with different inclination angle of the posterior implants (0 degrees, 15 degrees, 30 degrees, 45 degrees) were constructed. A static load of 150 N in the multivectoral direction was applied unilaterally to the cantilever region. The stress distributions in the peri-implant bone were evaluated before and after osseointegration. The principal tensile stress (sigma(max)), mean principal tensile stress (sigma(max)), principal compressive stress (sigma(min)) and mean principal compressive stress (sigma(min)) of the bone and micromotion at the contact interface between the bone and implants were calculated. In all the models, peak principal stresses occurred in the bone surrounding the left tilted implant. The highest sigma(max) and sigma(min) were all observed in the 0 degrees model for both immediate- and delayed-loading models. And the 0 degrees and 15 degrees models showed higher sigma(max) and sigma(min) values. The 0 degrees models showed the largest micromotion. The observed stress distribution was better in the 30 degrees and 45 degrees models than in the 0 degrees and 15 degrees models.