Reliability and validity of the instrumental assessment of implant stability in dry human mandibles

The aim of this study was to determine the intra- and interobserver reliability and validity of the instrumental assessment of primary dental implant stability, using resonance frequency analysis (RFA). Sixteen tapered implants and 16 cylindrical implants were installed in eight unfixed dry human mandibles (Cawood classification IV/V). Implant stability quotients (ISQ; the outcome variable of RFA) and peak removal torque were determined. Both the intra-observer reliability and the interobserver reliability of the RFA measurements were fair-to-good, while no significant correlations between the ISQ values and removal torque were found. The removal torque of the cylindrical implants was higher than that of the tapered implants. The smallest detectable difference was almost nine ISQ units. Within the limitations of the present dry cadaver study, it was concluded that (i) primary dental implant stability can be assessed reliably with RFA measurements, (ii) the concurrent validity between RFA measurements and removal torque is poor, (iii) cylindrical implants may be more stable than tapered ones and (iv) two subsequent readings of RFA measurements need to differ at least nine ISQ units before the difference between the two measurements can be considered statistically significant. More research is needed to see whether these conclusions can be extrapolated to the clinical situation, including the assessment of implants during function (secondary stability).