## 1 Introduction  
Intraoral scanners (IOSs) have demonstrated ceaseless development since their introduction in 1985; therefore, currently, a wide range of digital scanners are available for a dental practice, and the use of IOSs is part of the daily practice routine for a continuously increasing number of dentists [1, 2]. Numerous studies on IOS are available, most dealing with different aspects of accuracy, some addressing handling, and a few focusing on the further development and implementation of digital processes [3, 4, 5, 6, 7]. However, all these aspects are necessarily related to the capabilities of the actual scanners used in this study [8]. Although improvements have occurred over the years, the underlying reasons for the differences are difficult to distinguish as they may be related to the study setup,the operator's experience, or the scanners themselves. To the best of our knowledge, no study has compared different generations of scanner families in an identical study setup over the years. For each of the three different scanning principles (optical triangulation technique, active wavefront sampling, and confocal laser scanning systems), a typical scanner is included. As only a single scanner family uses active wavefront sampling, this family is also included, although the respective manufacturer will discontinue the scanner and the future of the system is unclear. A large number of studies have shown that various factors influence the accuracy of intraoral scans. To date, a lack of calibration [9], the scanning path [10; 11], and the users themselves [12] were identified as potentially influential factors. While IOS could already reach or even exceed the accuracy of conventional impressions for single teeth [13], the situation, for a long time, with regard to impressions of natural teeth, especially across the quadrant, was that IOS could not reach the level of accuracy of conventional impressions [14; 15]. However, in more recent studies, it was demonstrated that IOS impressions within a quadrant and even beyond could achieve even better results than with conventional impression methods [3; 16]. With regard to implant impressions, the results of a previous clinical study even showed similar results between conventional and digital impression methods when taking impressions of maxillary situations or partially edentulous jaw sections [4]. Comparable results were also obtained in other studies [17; 18]. Although IOS are constantly being developed and improved, only a few studies [19; 20; 21] are available where different software versions were examined and described as potentially influencing the transfer accuracy of IOS. However, within one study, only two different software versions of a scanner family were investigated with regard to the accuracy of single tooth preparations. It was found that the software version can have an influence on the result of the transfer accuracy [19]. In a further study, the influence of different parameters during the production of crowns was investigated. Two different software versions of a scanner were also used [20]. The most recent study on the influence of different software versions was investigated in relation to the accuracy of different restorative materials [21]. However, none of these studies investigated the influence on the transfer accuracy of implants. Furthermore, the transfer accuracy of implants by intraoral scanners is of specific interest, since implants have a tenfold lower mobility compared to natural teeth which requires an enormously high transfer accuracy from the oral situation to the model situation [22; 23]. For this reason, an implant model setup with a corresponding reference key offers excellent possibilities for standardization over the years, due to the fact that the implant model structures are precisely prefabricated and remain dimensionally stable over a long period of time. Thus, implant models represent identical basic situations.