Torsional resonance frequency analysis: a novel method for assessment of dental implant stability.
To establish and experimentally validate a novel resonance frequency analysis (RFA) method for measurement of dental implant stability by analyzing torsional resonance frequency (TRF). A numerical study and in vitro measurements were performed to evaluate the feasibility and reliability of the method of torsional RFA (T-RFA) using a T-shaped bilateral cantilever beam transducer. The sensitivity of this method was assessed by measuring the TRFs of dental implants with 8 sizes of T-shaped transducers during polymerization, which simulated the process of bone healing around an implant. The TRFs of the test implants detected using this new method and the bending resonance frequencies (BRFs) measured by Osstell(®) ISQ were compared. TRFs and BRFs on implant models in polymethyl methacrylate (PMMA) blocks with three exposure heights were also measured to assess the specificity of this method. Finite element analysis showed two bending modes (5333 and 6008 Hz) following a torsional mode (8992 Hz) in the lower rank frequency. During in vitro measurements, a bending formant (mean 6075 Hz) and a torsional formant (mean 10225 Hz) appeared, which were verified by multipoint measurement with invariable excitation frequency in the laboratory. In the self-curing resin experiments, the average growth rate at all time points of TRFs using the new method with Transducer II was 2.36% and that of BRFs using Osstell(®) ISQ was 1.97%. In the implant exposure height tests, the mean declined rate of TRFs was 2.06% and that of BRFs using Osstell(®) ISQ was 12.34%. A novel method for assessment of implant stability through TRF was established using a T-shape transducer, which showed high reliability and sensibility. The method alleviated the effects of implant exposure height on the measurements compared with Osstell(®) ISQ. The application of T-RFA represents another way in the investigation of dental implant osseointegration.