The computed ISQ value is based on the following calculation formulae:

Hereby, f denotes the measured maximum resonance frequency (RF). Coefficients a, b, c, d, and e are property information of Osstell (Osstell AB, Gothenburg, Sweden). The coefficients were provided for internal use under the agreement of no publication. From clinical reports [10,11,12,13,14,15,16] listed in Table 1, it can be concluded that ISQ values for one specific implant system, inserted in comparable jawbone regions, differ considerably between outcomes obtained by the original wired Osstell device and the more recent Osstell Mentor device. These findings were confirmed in both a clinical trial with an approximate difference of 9 ISQ units [16] and in vitro on human cadaver jawbone with an approximate difference of 10 ISQ units [17]. This means that the comparison of clinical studies reporting implant stability outcomes generated by different versions of Osstell devices in (systematic) reviews needs caution and correction.

The purpose of this in vitro study was to develop a laboratory method, intended for future research of aspects of implant-Smartpeg complex stiffness and its possible influence on the overall RFA-based implant stability determination. For this, a combination of laser Doppler vibrometry for measurement and signal processing by aid of fast Fourier transformation analysis was used. Laser Doppler vibrometry technology permits to determine both the resonance frequency and deflection behavior of a mounted Smartpeg. The latter can be of interest since different implant types possess different prosthetic connections that suit different types of Smartpegs. In vitro research enables to control and simulate in a standardized way the stiffness of the surrounding bone and the stiffness of the implant-bone complex by imbedding implants in self-curing resin. Complete imbedding of the implant to the most coronal level simulates a normal clinical situation of total osseointegration. Incomplete imbedding allows to both measure the deflection mode of the Smartpeg and the implant itself when different vertical points are used to execute the measurement (Fig. 1).