## 1 Introduction  
Implant stability is critical in implant therapy and varies during the osseointegration process, reflecting bone/implant interface changes [1, 2]. Low levels of implant micromotion are necessary to avoid implant failure and to achieve successful osseointegration [3, 4, 5].  
Several existing methods have addressed measuring implant stability, including theoretical [6] and experimental modal analysis [7]. Among these, Perioest, insertion torque value (ITV), and implant stability quotient (ISQ) using resonance frequency analysis [8] are the ones widely used clinically. Periotest is a damping method that requires to strike the implant abutment [9], ITV measures the newton centimeters used to screw the implant into the bone [5], and ISQ sensors register the response of the electromagnetic stimulation of an abutment fixed to the implant called transducer peg, measuring the implant stability [10]. Periotest and ISQ are considered modal analysis methods based on the displacement signal secondary to an external impulse force [7]. Successfully integrated implants involve low implant micromotion levels, which usually correspond to low Periotest values and high ITV and ISQ values. These ITV and ISQ values are inversely correlated with low implant micromotion. However, the relationship between ITV and implant micromotion becomes exponential for higher ITV values [5]. Besides, ITV only measures implant stability at the moment of the insertion [8]. For these reasons, ISQ is usually the preferred method to measure implant stability.  
Devices used to measure ISQ return a quotient value ranged from 0 to 100 corresponding to minimum and maximum vibration, respectively [11]. According to existing literature, a minimum ISQ value of 57 corresponds to a maximum implant micromotion of 150 \(\upmu\)m. Clinically, this micromotion represents implant stability and it is required to maintain osseointegration [2,5].  
There are several studies analyzing the reliability of existing devices for measuring the ISQ. These analyses have focused on two devices: Oostell(r) (W&H, Goteborg, Sweden) and Penguin(r) (Integration Diagnostics Sweden AB, Goteborg, Sweden) [12, 13, 14]. For instance, [PERSON] et al. [12] reported better reliability for Oostell(r), while [PERSON] et al. [13] reported that both devices were sensitive and reliable. [PERSON] et al. reported excellent reliability for Penguin(r), but they did not report the reliability of Oostell(r) [14]. [PERSON] et al. [15] reported the agreement between the measurements obtained by two different Oostell(r) versions and Penguin(r), and the authors considered these differences not clinically relevant. Therefore, reliability results reported so far are contradictory.  
Oostell(r) Beacon is the wireless version of Oostell(r) that can be connected online to the Oostell(r) database for statistical analysis. The smartphones for Ostell(r) are not autoclavable. On the other hand, the multipegs for Penguin(r) are autoclavable and the device is wireless. MegaISQ(r) (Megagen Implant CO, Daegu, Korea) is a portable, but not wireless device that uses the Oostell(r) smartphones. To the best of our knowledge, inter- and intra-rater reliability and agreement among Oostell(r) Beacon, Penguin(r) and MegaISQ(r) have not yet been investigated.  
The goal of this study was to determine and compare the inter- and intra-rater reliability of Oostell(r) Beacon and MegaISQ(r) versus Penguin(r) as control. This study also aimed to explore the agreement between these devices for ISQ measurement. This study was conducted in vitro by two investigators to obtain the inter- and intra-rater reliability and the agreement level among these three devices.