Parameters of implant stability measurements based on resonance frequency and damping capacity: a comparative finite element analysis.

PURPOSE: Contradictory results have been reported on the comparability of implant stability measurements performed with the Periotest and the Osstell Mentor devices. The purpose of the present finite element analysis was to simulate the influence of the parameters implant length, bone quality (cortical thickness and damping factor), bone loss, and quality of transducer fixation on resonance frequency analysis (RFA) and damping capacity measurements. MATERIALS AND METHODS: Three-dimensional finite element models of implants placed in human mandibular bone were designed for the simulation of Periotest (Periotest value; PTV) and RFA (implant stability quotient) measurements. Three values for each of the parameters implant length, damping capacity of cortical and trabecular bone, thickness of cortical bone, bone loss, and quality of transducer fixation were obtained. Measurements were simulated at four stages of osseointegration. RESULTS: For all parameters, an increase in implant stability was found with increasing levels of osseointegration. Implant stability was positively correlated with implant length and thickness of cortical bone, with slightly converging values at increased levels of osseointegration. Varying the damping factor of bone had no significant effect. Implant stability was negatively correlated with bone loss, with slightly converging values at increased levels of osseointegration. Linear changes in implant length and bone loss caused nonlinear effects in implant stability values. Stiffness of transducer fixation had an impact on RFA measurements when values below 10 GPa were applied. CONCLUSION: Although both measuring devices reacted similarly when different parameters of implant stability were changed, good correlation between Periotest values and implant stability quotients was observed only when measurement values of implants without bone loss were considered.

Bone loading caused by different types of misfits of implant-supported fixed dental prostheses: a three-dimensional finite element analysis based on experimental results.

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.