At present, multiple implant stability assessment methodologies are used, both of invasive and non-invasive nature, including percussion test [1], X-ray evaluation [2], cutting resistance during implant insertion (e.g., electronic insertion torque determination) [3], turn-out or reverse torque test [4], Periotest® [5, 6], and resonance frequency analysis (“RFA”), e.g., the Osstell method [7, 8]. The validity of those methods can be evaluated to their sensitivity to detect small changes in stability that are not detectable with clinical and/or radiographical methods. Electronic devices such as insertion torque devices, Periotest, and Osstell Mentor devices are commercially available instruments that allow quantitative implant stability analysis at a level that is not feasible with traditional clinical or radiographical methods [9]. The Osstell device methodology is based on quantitative assessment of (micro) deflection of the implant—by aid as a transducer—in the surrounding jawbone, induced by controlled appliance of electromagnetic excitation. The properties of a transducer (e.g., stiffness and screw properties), the stiffness of the “implant-transducer” complex, the properties and stiffness of “implant-bone” complex, e.g., the effective height of the coronal implant part above the bone crest [7, 8], and the stiffness of the bone itself are measurement influencing factors (Integration Diagnostics Company®, Osstell mathematical explanation, 2009).

In the past, various versions of the Osstell device  have been developed and marketed. The original version consisted of a wired version of the transducer. The transducer consisted of two built-in piezoceramic elements. One piezoceramic element served as the transmittor element, receiving an electrically generated sine wave with varying frequency. The response signal was analyzed by an oscilloscope with the resonance frequency in kilohertz as the outcome unit.

The launch of the Osstell Mentor® in 2004 included the introduction of a less voluminous, much more user-friendly, non-cabled transducer, called Smartpeg. Smartpegs are small aluminum rods with three different parts: a coronal part with an implant system-specific screw fitting into the individual implant, a hexagon part enabling easy tightening/un-tightening, and a magnet serving as the electromagnetic puls captor. The apparatus itself was a compact device with an incorporated microcomputer and electromagnetic signal emitting and receiving tipped probe. Excitation of the implant-mounted Smartpeg is performed by four electromagnetic pulses with different frequencies inducing Smartpeg vibration in mostly two directions perpendicular to each other. The vibration directions correspond to a low and a high resonance frequency. The manufacturer recommends performing at least two measurements, in order to identify these possible different stabilities. Furthermore, in order to suppress electromagnetic environmental noise, the working principle is refined by four times repeated emission of each excitation frequency. In summary, 16 pulses are emitted for each single measurement. The captured outcome of each in fourfold emitted signal is converted by the built-in microcomputer into a frequency spectrum by a “fast Fourier transformation” (FFT) method, ending up to detect among the four calculated spectra the two highest peaks representing the resonance frequencies of the implant. The latter will be used to calculate the so-called implant stability quotients (ISQ) by aid of a mathematical algorithm. ISQ is a unitless number, ranging between 0 and 100. If the difference between the two peaks is less than 3 ISQ units, or in case of only one peak detection, only 1 ISQ value will be displayed by the microcomputer. The 2009 Osstell ISQ version and the present Osstell IDx® version do make use of the same algorithm.