**8. RFA**

Resonance Frequency Analysis for implant stability was first proposed by Merideth in his 1996 [8]. The first resonance frequency device was developed by Osstell and the device consisted of an L-shaped receiver that mounted on the implant and a transducer that pulsed it with a magnetic frequency.

Resonance Frequency Analysis (RFA) is the measurement of the frequency with which a device vibrates (**Figure 5**). RFA measurements reflect the micro-mobility of dental implants, which in turn is determined by the bone density at the implant site [9].

A transducer connected to the implant is excited by means of an electric or magnetic impulse (depending on the type of transducer used). Thus, the implant is subjected to slight lateral force that causes lateral displacement due to elastic deformation of the bone. The frequency of the registered oscillation depends on the stiffness of bone-implant attachment: the stiffer the system is, the higher the transducer's oscillation frequency will be. While most tests render subjective results, RFA allows objective, noninvasive assessment of implant stability [10].

Why is the measurement of lateral stability important? If an implant repeatedly moves laterally in the range of 100–150 microns, the body will not form bone at the implant-bone interface, instead, soft tissue will form and the resulting encapsulation of the implant in soft tissue will result in a failure.

ISQ is short for *Implant Stability Quotient.* The ISQ-scale runs from 1 to 100 and corresponds to the resonance frequency in a close to linear way. The scale was determined in 2003, and ISQ 1 correspond approximately to 1,000 Hz and ISQ 100 correspond approximately to 10,000 Hz. The early scientific studies were used to determine how the ISQ scale should relate to Hz and numerous clinical studies after that have put the ISQ-scale in a clinical context, relating to treatment and loading protocols.

The developed ISQ scales which are used today give the practitioner a way to quantitatively assess an implants stability. Developed over time by comparing clinical outcomes to ISQ values, thousands of scientific articles have been written that back up the validity of this type of testing device.

The following chart shows the various landmark values for ISQ and what they mean clinically (**Figure 6**). These values are pivotal to successful treatment and not only help direct the initial treatment with regard to deciding on a one stage vs. two stage surgery, but also the progression of healing and the correct time period in which to restore.
