PURPOSE
To show, by comparison of horizontal, vertical, and angular misfit in a three-dimensional finite element model, that clinical methods for the evaluation of implant framework fit cannot provide objective results.
MATERIALS AND METHODS
Two three-dimensional finite element models were designed for the simulation of experimentally determined strain values of three-unit fixed dental prostheses supported by two implants. Horizontal, vertical, and angular misfits between implants and restorations were used to create predetermined strain levels. The magnitudes of misfit and resulting bone loading were recorded as von Mises equivalent stresses for the different types of misfit.
RESULTS
A horizontal misfit of 36 μm and a vertical misfit of 79 μm had to be modeled to simulate the experimentally determined strain values. An angular misfit of 0.083 degree (equivalent to a gap of 3 μm on one aspect of the implant) resulted in comparable strain levels. Bone loading in the cortical area around both implants ranged from 50 to 90 MPa for horizontal and vertical misfit. In trabecular bone, loading of 2 to 5 MPa was found. For the angular misfit, bone loading up to 20 MPa in the cortical layer and 1 MPa in the cervical part of the trabecular bone occurred at the implant where the misfit had been introduced. Horizontal and vertical misfits led to comparable loading patterns around both supporting implants. Under angular misfit, bone loading mainly occurred around the implant where the misfit had been introduced. Almost no loading was observed in the circumference of the contralateral implant.
CONCLUSIONS
Minimal angular misfits between implant abutments and restorations, which cannot be detected clinically, may lead to substantial bone loading.