Implant Stability Measurements Using Torsional Vibration Resonance Frequency Analysis:an In Vitro Model Study

Background: Resonance Frequency Analysis (RFA) was first described by Meredith[1,2,3,4]in the1990s for assessing the stability of dental implant. At present, RFA isconsidered to be an ideal technique for clinical assessment on osseointegration of implants.However, the current RFA researches still focus on the bending resonance frequency thatis easy to be identified and obtained[5]. As a parameter to monitor implant stability, thevalue of RFA is in doubt, wich is influenced by many factors[6,7,8,9], such as the design ofthe transducer itself, the effective length (implant exposure height), bone tissuecharacteristics, inserting torque value, the stiffness of implant and bone-implant interface.Objectives: Based on the previous theoretical researches of RFA in an finite elementanalysis[10,11], we developed a new method for the measurement of dental implant stabilityby analyzing torsional resonance frequency. The aim of this study was to evaluate thereliability, sensitivity and specificity of this new RFA method by finite element analysis and in vitro model experiments.Material and Methods: A numerical study was first performed to evaluate thefeasibility of this method on the resonant modes of implant-transducer in a resin blockmodel. After that, the new method was established in the laboratory with the reliabilityand sensitivity being evaluated. The final design of this new transducer was identified bystudying the influence of its size with torsional resonance frequency in a self-curing resinexperiment. Finally, the specificity experiment of this new method had been made in aresin block and goat bone models by studying the effect of the exposure height and bonestructure.Results: Finite element analysis showed that there were two bending modes ofimplant-transducer (f1=5333Hz，f2=6008Hz) that followed a torsional mode (f3=8992Hz) in the lower ranks frequency. In the lab, a bending vibration (resonancefrequency:6075.5±24.4Hz) and a torsional vibration (resonance frequency:10225±18.4Hz), which had been confirmed by a fixed-frequency excitation with multi-pointmeasurement method, were appearing. In the self-curing resin experiment simulated bonehealing process, this new method with the TransducerⅡ (14mm in length and1.5mm inthickness) was more sensitive for the changes of the implant-resin interfacial stiffness thanOsstell ISQ (average growth rate:2.36%±0.03VS.1.97%±0.02). In the specificityexperiment for this new method, the torsional vibration resonance frequency was affectedless by the implant exposure height than Osstell ISQ (average dropped rate:2.06%vs.12.34%in resin block and8.19%vs.13.40%in bone block).Conclusion: This study established a new RFA method with torsional vibrationresonance frequency assessment of implant stability by using a T-shape transducer. Resultsshowed that the method had high reliability. Compared with the Osstell ISQ, this newmethod showed a higher sensitivity for the changing interfacial stiffness of implants.Besides, the method made the implant exposure height effect less on the measurementresults than Osstell ISQ. The application of torsional vibration resonance frequencyanalysis represents another way in evaluating osseointegration of dental implant.