## 4 Discussion
This pattern is consistent with the findings of [PERSON] et al., who, in an in vitro investigation compared the accuracy of a conventional analogue impression, two intraoral scanners, and a photogrammetry-based system, finding that the photogrammetry device yielded the lowest accuracy and the largest discrepancies [30]. It is worth noting, however, that the literature presents conflicting results, with some studies reporting lower discrepancy values for impressions obtained using photogrammetry-based systems [4; 6; 43]. Several references in the literature propose accuracy thresholds aimed at minimizing clinical complications related to misfit in implant-supported prostheses, such as screw loosening or even the fracture of abutments and screws [14; 44; 45]. Among the reported values, a threshold of 30 \(\upmu\)m is widely recognized and is considered the lowest and most stringent safety limit identified in the reviewed literature; therefore, it was adopted as the reference value in the present study [18; 20]. Although differences were observed among the tested scanners, the distance deviation values for all devices (ranging from 13.65 to 58.80 \(\upmu\)m) remained below the maximum clinically acceptable misfit threshold of reported in the literature [11; 46]. In terms of the influence of implant distribution on trueness, the findings of this study indicate that fewer implants placed in closer proximity resulted in improved results. Specifically, the CCI C distribution, involving closely spaced implants, demonstrated the lowest RMS values in the trueness evaluation. This aligns with previous research, which has reported statistically significant differences among impression techniques when scanning four or six implants [47]. In the current study, both the number and spatial arrangement of implants were analyzed. The results showed that the four implants located in the anterior region (CCI C) produced more accurate outcomes than the same number of implants placed farther apart (CCI B). These findings support the premise that a reduced number of implants with minimal inter-implant distance contributes to improved passive fit. Consistent with the existing literature, the absence of mucosal landmarks is associated with reduced accuracy in digital impressions [18; 48; 49; 50]. Despite methodological differences, studies by [PERSON] et al. and [PERSON] [PERSON] et al. also concluded that implant positioning significantly affects trueness [51; 52]. Although informative, this study is not without limitations. One of them is the reliance on RMS values obtained from 3D comparisons to assess trueness. As above mentioned, these values represent the mean of overall deviations and do not allow for implant-specific analysis of trueness [40]. Another limitation is the use of in vitro conditions for the impression procedures, which may not fully replicate clinical scenarios. This could result in an underestimation of deviations typically introduced by patient-related variables such as blood, saliva, tongue movement, soft tissue dynamics, and ambient lighting conditions [53]. It is essential to highlight that intraoral scanners in this study were used under controlled, optimal conditions, free from the presence of the aforementioned variables. As such, their clinical performance may not fully reflect the trueness observed in vitro. On the other hand, photogrammetry-based systems are expected to maintain a comparable level of accuracy in real-world settings. These systems have gained attention as a viable alternative for full-arch implant impressions, as they may help overcome certain limitations associated with intraoral scanning [4]. In clinical contexts where mucosal movement and absence of stable reference structures pose challenges, the unique design and acquisition method of photogrammetry devices, may offer greater reliability and ease of use compared to IOSs [27, 30]. At present, photogrammetry systems are expensive and are primarily intended to be used in implant impressions.