## 4 Discussion
Specifically, their in vitro study compared the accuracy of a conventional analogimpression, two IOs, and a photogrammetry-based scanner, with the latter presenting the least accurate results and the highest discrepancy values [38]. However, these findings are not consistent across the literature, as other studies have reported lower discrepancy values for photogrammetry-based impressions [22; 23]. A number of references to safety values of precision can be found in the literature to prevent clinical complications associated with the misfit of implant-supported prostheses, such as unscrewing of structures or even fracture of screws and abutments [3; 41; 42]. Of these, 30 um is the most consensual value and is described as the one with the greatest precision, and it was therefore considered for this study [14; 32]. Based on this cutoff value, and as previously mentioned, all digital impression methods assessed demonstrated high performance with low RMS values, showing an average discrepancy close to 12 um for all devices. With respect to the impact of implant distribution on precision parameters, this study demonstrated that a smaller number of implants in closer proximity yields better results, as the CCI C implant distribution showed the lowest RMS values in the precision assessment. As reported in other studies, statistically significant differences were found between impression methods when scanning four or six implants [43]. In the present study, in addition to varying implant numbers, different spatial positions were also evaluated. According to the results, four implants placed in the anterior region (CCI C) produced better results than four implants positioned more distantly (CCI B). Therefore, our data support the idea that a reduced number of implants in closer proximity favors better passivity results. As noted in the literature, the absence of reference points on the mucosa leads to lower precision in digital impressions [14; 16; 19; 27; 44]. While valuable, our study has certain constraints. One limitation is the assessment of precision based on RMS values derived from 3D comparisons: as discussed above, these values represent the global average of discrepancies and do not allow for an individual interpretation of results, considering the position of each implant [34]. Another limitation is the lack of a control group (i.e., conventional impressions) [12]. Finally, the use of in vitro conditions for the scanning procedures also represents a limitation of this study, which may have underestimated deviations caused by intrinsic patient factors such as saliva, blood, tongue movements, soft tissues, and lighting conditions [45]. It is important to emphasize that IO scanners were used under ideal conditions, i.e., in the absence of blood, saliva, and mobile tissues. Consequently, it can be anticipated that their performance in clinical practice may be inferior to the in vitro results, whereas photogrammetry-based scanning is likely to maintain comparable precision under similar conditions. In fact, photogrammetry-based impressions have emerged as a promising alternative to IOs for full-arch implant impressions, as they may address some of these limitations [25]. Due to its equipment features and impression techniques, photogrammetry may present fewer challenges than IOs [38; 46]. Photogrammetry systems are costly and primarily designed for implant scanning rather than general-purpose intraoral digitization. As this technology exclusively records the positional data of implant abutments within the patient's oral cavity, the complementary use of conventional IOs is required to capture soft tissue information [22]. Consequently, the cost-benefit ratio of photogrammetry should be carefully evaluated. However, the use of photogrammetry based on open-source software has been described in the literature as a means of obtaining digital models at minimal expense, thus presenting an appealing option for dental students and young practitioners seeking to adopt digital dental workflows [47].