Mechanical testing methods like reverse torque, or “pullout test,” have been used to study and measure the mechanical interface between implant and bone in various ways [22, 23]. The Branemark group has evaluated the mechanical properties of osseointegrated implants using torsion and pullout tests and lateral loading tests [24, 25]. Presence or absence of mobility and the bone level around the implant can be estimated by non-invasive methods based on resonance frequency analysis (RFA) such as those used by Periotest and Osstell™ devices [26–30].

Resonance frequency analysis has been used to document changes in the bone healing along the implant-bone interface by measuring the stiffness of implant in the bone tissue [31–34]. It has also been used to determine whether implants are ready for the final restoration [35] or ready to be loaded [33] and to identify the implants at “risk” [36]. The first studies using RFA were published in 1996 [37]. In 1997, Meredith et al. suggested a non-invasive method for determining the resonance frequency associated with dental implants by connecting an adapter/transducer onto the abutment in an animal study [38]. The experimented RFA system, base on magnetic pulses, has been commercially produced as Osstell since the year 2000 [19] (Osstell AB, Göteborg, Sweden). Osstell was later followed by Osstell Mentor™ and Osstell ISQ™. It calculates the Implant Stability Quotient (ISQ) converting kilohertz units to ISQ on a scale of 1–100, where 100 signifies the highest implant stability. Increases in ISQ measurements indicate improved bone stiffness and healing around the implant and better implant stability. The Osstell ISQ works by introducing a controlled vibration to the implant by means of a sensor and a rod (SmartPeg) connected to the implant and measuring its frequency. These SmartPegs are usually fabricated for standard diameter implants. The osseointegration potential of single-piece mini dental implants (3M™ESPE™ MDIs) has never been assessed by RFA. The immediate post-surgical ISQ assessment of MDIs is particularly relevant due to their smaller size and surface area in comparison to standard implants.