## 4 Discussion
The authors compared the accuracy of digital and conventional implant impressions for completely edentulous patients without assessing the framework fit. The authors calculated the 3D deviations between the virtual casts from intraoral full-arch digital scans and digitized final stone casts generated from conventional implant impressions. The results of the 3D deviations were 162 \(\pm\) 77 \(\upmu\)m. The findings did not display any misfit among implant and framework, but the superimposition of two virtual casts. Therefore, it is difficult to interpret the results due to the lack of consideration of milled frameworks. Moreover, the average value reported is beyond the clinically acceptable threshold [15; 16; 17]. However, several in vitro articles demonstrated better fit values for the digital rather than the traditional approach [24; 28]. [PERSON] et al. [28] compared different impression techniques on multiple implants by using a coordinate measurement machine (CMM). After CMM analysis, the best and the worst casts generated using digital and traditional impressions were selected to mill titanium frameworks. The Sheffield test showed that the framework milled by the worst cast generated using the traditional impression presented the highest mean gap value (63 \(\upmu\)m). Therefore, the digital impressions represent a viable alternative to traditional impressions to realize the framework of full-arch implant-supported FDPs. Furthermore, [PERSON] et al. [24] reported a mean misfit value <30 \(\upmu\)m for the framework of a full-arch implant-supported FDP realized using a digital impression. Similar results were obtained in this research, where the average misfit value was 38 \(\pm\) 5 \(\upmu\)m. The statistical analysis showed significant differences among the misfit values of implants in central positions compared with the other values. Indeed, the mean misfit values in positions 3 and 4 were 42 \(\upmu\)m and 45 \(\upmu\)m, respectively. The mean values were higher than the misfit mean values in the other positions. This result reveals a possible issue that the IOS may encounter during the acquisition of the central area due to the arch. Therefore, the correct scan strategy is fundamental to avoid this problem. The choice of the best impression techniques is a strategic step to ensure success and survival in prosthetic rehabilitation. With the increasing interest in the digital field, clinical articles may be useful to illustrate the advantages and disadvantages of these devices. This research presents several limitations. The first is the impossibility of analyzing in vivo the mean value of misfit for the framework. Instead, we utilized an in vitro procedure where the interface among the analog and framework is measured with the use of a microscope. The second limitation is the use of only the Sheffield test to assess the in vivo misfit. Another limitation is that the X-ray examination was conducted only on one framework; therefore, the result cannot be generalized to other frameworks. The reason for this was to prevent unnecessary exposure of the patient to radiation. However, this study suggests only that the digital implant impression with the iTero represents a valid method to mill full-arch implant frameworks. The result is not applicable to all intra-oral scanners; therefore, further in vivo studies are required to investigate the performance of other devices.