## 1 Introduction  
Implant stability can be defined as an absence of clinical implant mobility and consists of primary and secondary implant stability [1]. Primary stability includes the mechanical attachment of an implant in the surrounding bone at the insertion, whereas secondary implant stability is the tissue response to the implant and subsequent bone remodeling processes. Primary implant stability is known to be a crucial factor for successful osseointegration of dental implants [2; 3]. There is sufficient evidence to accept a positive correlation between primary implant stability and implant success, as the success relies on the sustainable integration of the implants into hard and soft tissues [3; 4; 5; 6]. Secondary stability depends on primary stability and has been reported to increase four weeks after implant placement [7,8]. Thus, in the first 2-3 weeks after implant placement, a stability gap with the lowest implant stability is expected [9]. Various methods have been used to examine implant stability at insertion and during the osseointegration period [7]. In 1996, resonance frequency analysis (RFA), as a noninvasive method to investigate the stiffness and stability of the implant-bone interface, was introduced by [PERSON] et al. [10]. The resonance frequency analysis (RFA) is a measurement of the frequency of a vibrating device. The measurement is performed by a frequency modulator, which exerts a vibration on a sensor (adapter) firmly attached to the implant. The frequency modulator vibrates the adapter at a frequency of 5 to 15 kHz. The vibration of the sensor is positively correlated with implant stability (i.e., stiffness of the bone-implant interface) [1]. The measurement of implant stability is the implant stability quotient (ISQ) and ranges from 1 (lowest implant stability) to 100 (highest implant stability) [1,5]. Reported ISQ values for successful implants range from 57 to 82 [9]. However, ISQ values at implant insertion should be \(\geq\)60 to achieve sufficient implant stability [11,12]. It is suggested that implants with high ISQ-values show lower micro-motions and withstand higher forces in the mouth [11,12]. For the immediate loading of dental implants, ISQ values of 60-65 were associated with a good prognosis [13]. Moreover, several studies have confirmed that RFA measurements are able to successfully predict implant failure [14, 15, 16, 17]. Immediate loading protocols are of interest for modern implant therapy since the technique of implant placements immediately following tooth extraction was introduced in the 1970s [18]. Several concerns with two-stage approaches have been stated, such as alveolar bone loss, increased time of edentulism and surgery, need for a second surgical procedure, and psychological factors associated with the aforementioned limitations [19]. In contrast, the implants' immediate placement in the fresh extraction socket as a one-step procedure reduces the length of surgery as well as the number of interventions, and, consequently, has psychological benefits for patients [19, 20, 21]. In a recent systematic review conducted by [PERSON] et al., immediate placement of a single tooth was associated with a higher risk for early implant loss compared to delayed implant placement [22]. All implant failures were early failures resulting from a lack of osseointegration. As the success of immediate loading approaches directly relies on primary stability, prognostic factors are of interest for preoperative risk-stratification models. Further, innovative surgical techniques, such as ultrasonic site preparation, can be included with the methodology provided to assess other predicting factors in the future [23]. Several recent studies focused on the assessment of implant stability based on radiofrequency analysis [24, 25, 26, 27, 28, 29]. However, these studies focused on the differences between implant systems and characteristics without considering confounding factors to predict implant stability for future risk stratification models.