Relevance of resonance frequency analysis to evaluate dental implant stability: simulation and histomorphometrical animal experiments

Background: Resonance frequency analysis (RFA) is applied to evaluate implant stability, and the clinical relevance of this application is accepted. However, a discrepancy between resonance frequency (RF) and other parameters of implant stability such as implant insertion torque and bone mineral density at the insertion site has been reported. In addition, the relation between RF and histological implant-bone contact has not been well documented. Purpose: To explain this discrepancy and to clarify the relation between RF and histological implant-bone contact, we conducted the present study. Materials and methods: A hydroxyapatite-coated implant, 4 mm diameter and 10 mm length, was used. We placed the implant in a small plastic box vertically and fixed the implant in the box with small screws at different height positions. An 'Osstell' transducer was mounted on the implant and RF was measured with or without loosening the screws. Twenty-four implants were placed in the tibiae of four mini-pigs. The animals were sacrificed 1, 2 and 4 weeks after the placement, and the RF of each implant was measured. Ground sections were prepared and implant-bone contact was histomophometrically measured. Results: Loosening the screw at the neck region of the implant remarkably decreased RF compared with the screws of the other regions. Correlation between RF and implant-bone contact, which was measured all around the implant, was not significant (r=0.221, P=0.299). However, the correlation coefficient increased to '0.361' when implant-bone contact was measured at the neck of the implant (P=0.0835), although these two parameters were not statistically correlated. Conclusions: Although RF did not correlate with histological implant-bone contact, the present results demonstrated that a connection between the implant and bone at the neck region of the implant affects RF the most effectively, further suggesting the superiority of RFA in the process of implant treatment and the follow-up. The present results could explain the discrepancy between RFA and other parameters of implant stability.