## 4 Discussion
Although this method is commonly used according to the ISO standard, different approaches to the evaluation of precision were reported [37,38]. In principle, the comparison to other studies is difficult, since only a few studies use an RC, and these alone allow a three-dimensional evaluation. Furthermore, clinical studies tend to a lower trueness due to the presence of saliva and possible movements of the patient. When comparing the results to the literature, the respective date of publication as well as the hardware and software version used within the respective study must be taken into account. With regard to the results of TD_4.1, similar results were obtained in a study by [PERSON] et al. [39, 40]. Similar values were also obtained for the angular changes as in the present study. The results of the TR2 are comparable to a study by [PERSON] et al. [41, 42], and the results of the study by [PERSON] et al. [43]. The results of OC_4.2 were remarkably high for all measurements. These results could be confirmed by a study by [PERSON] et al. [44]. Within a clinical study by [PERSON] et al. [14], even higher values could be determined. In contrast, investigations by [PERSON] et al. [11, 34] showed more accurate results for the Omnicam with the old software version. However, it must be noted that the upper and lower 10-20% of the measured values were not included in the results due to the evaluation. However, this reflects exactly the extreme values of the deviations to which the old software version could tend. With regard to the digital impressions conducted with the new hardware and software versions, higher deviations could be measured within an investigation by [PERSON] et al. [45]. However, this may be due to a different evaluation method of the linear distances. Lower deviations were found in investigations by [PERSON] et al. [46], [PERSON] et al. [18], and [PERSON] et al. [47]. It is hypothesized that the small distances between the implants are decisive factors which typically cause only small deviations in the transfer accuracy. Similar results were obtained by [PERSON] et al. [17], [PERSON] et al. [48], [PERSON] et al. [49], [PERSON] et al. [50], and [PERSON] et al. [51]. Nevertheless, other studies report similar results for the CI in an accuracy range of 11 to 70 micrometers such as studies by [PERSON] et al. [52], [PERSON] et al. [45], [PERSON] et al., [PERSON] et al. [50], and [PERSON] et al. [47]. The inaccuracies in the older optical triangulation technique and confocal scanners increased with the progression of the scan path. It is hypothesized that the ongoing increase in the inaccuracies from the start of scan path (implant 14) to the end of scanning path (26) was related to the summation of errors from the partial incomplete superimposition of the scanned images. These results are consistent with those of earlier studies [43, 49], except for in [17], where no increase in errors with the progress of the scan path was observed for optical triangulation and active wavefront sampling systems. However, this difference may be due to a possible camouflage effect of the best-fit algorithm [25] used in the study from [PERSON] et al. [17]. However, this challenge appears to diminish in more recent scanners, which has also been described by [PERSON] et al. [53]. As anticipated, the results for the conventional impressions were not affected by the implant position, which is consistent with previous studies [14, 17]. The partially higher deviations regarding the absolute 3D deviations are due to the necessary pull-off forces from the model, which were unavoidable owing to the plane-parallel reference bodies present in the model. It can be assumed that these are lower in the patient; however, there may also be undercuts in clinical situations. It was found that the conventional impressions showed higher inaccuracies, particularly in the rotation and angulation deviations.