The Smartpeg excitation mode was exactly performed as described above. Notation of the maximum resonance frequency for indirect measurements is followed by notation of direct ISQ value on the display of Osstell IDx device. Positioning of the probe was not changed during indirect and direct recordings for a given test implant.

Each resin block contained five identical implants with attached Smartpegs of a given implant type with a specific diameter and length configuration. Correct positioning of the Osstell probe towards the Smartpeg magnet part was confirmed by the auditory signal generated by the Osstell device. Correct positioning of the vibrometer laser beam was checked by the visual reflection indicator on the vibrometer display.

The output signal of the laser Doppler vibrometer was linked through an ADC/frontend interface (3160-A-4/2 (Bruëll & Kjaër, Nærum, Denmark) to a laptop with signal processing software (Bruëll & Kjaër Pulse Labshop, Bruëll & Kjaër Nærum, Denmark) to convert the speed of resonance v(t) into a resonance frequency v(f) using the autospectrum function.

The software enabled to analyze the continuously monitored input signal from the laser vibrometer. The measurement period was set at 31.25 ms. The time signal v(t) was processed through a fast Fourier transformation (“FFT”) analysis V(f), resulting in a frequency span ranging between 0 and 12.58 kHz with 400 frequency intervals, resulting in a frequency resolution of 32 Hz. The FFT analysis generates a so-called autospectrum, based on the following formulae:

with V ^∗(f) being the complex conjugate of V(f).

The final generated autospectrum pointed the maximum resonance frequency value based on an average of 1000 measurements per detection session (Fig. 3). This recorded maximum resonance vibration frequency was noted in the datafile. The measurement was done in fivefold, and a mean value of all five measurements was computed, serving as the value to be input in the Osstell algorithm. Secondly, the “direct” ISQ value generated by the Osstell device was also noted in the datafile. After completion of measurements for each out of the five implants in each resin blocks, measurements were repeated in fourfold. In total, five measurements were made for each test implant.