## 4 Discussion
### Artificial Landmarks to Improve the Accuracy of IOSs
For the scanning patterns of the SS and QU groups, the LD artificial landmark was found to have the lowest RMS values of trueness, while the highest RMS values of trueness were recorded in the CON and FL artificial landmarks (all \(p<0.05\)). Artificial landmarks and scanning patterns affected the RMS values of precision. In each artificial landmark group, QU scanning patterns were found to have the lowest RMS values of precision (all \(p<0.05\)). For the scanning patterns of the LB and QU groups, LD and FL artificial landmarks were found to have the lowest RMS values of precision, while the highest RMS values of precision were recorded in the CON artificial landmark (all \(p<0.05\)). The present study showed that liquid dam markers were significantly more accurate than the other artificial landmarks. The complete-arch implant intraaoral digital scans without artificial landmarks were less accurate than the other groups. Regarding the scanning pattern, the accuracy of the quadrant pattern was significantly higher than in the others. However, the results were contradicted by a previous study, which reported that scanning patterns did not significantly affect the accuracy when recording long-span digital scans with a Trios intraoral scanner [38]. In all previous studies, the artificial landmarks were positioned on the alveolar ridge [28,30]. In 2022, [PERSON] et al. studied the effect of different artificial landmarks (bar or plates) attached to the dorsal palate on the accuracy of complete arch scans using the Primescan (Dentsply Sirona) IOS [31]. A test model (M) was produced that simulated a patient who was treated with a complete-arch fixed partial denture (FPD). Five ceramic precision balls (Optische Kalibrierkugel TOPIC white; Saphirwerk AG) were used for the calibration, and the center point of these balls were numbered with P1 next to the right second molar, P2 next to the left second molar, P3 next to the incisors, P4 next to the right canine, and P5 next to the left canine. The two different artificial landmarks used were a bar (B) and four plates (P) in the dorsal palate, designed with structured and geometrically nonidentical surfaces. The artificial landmarks were stereolithographically produced in a tooth-colored resin (FREEPRINT temp; Detax). For each of the three methods (manufacturer scan, bar scan, plates scan), the model was scanned 30 times by an experienced investigator. The scans were postprocessed using the manufacturer's software program and exported in standard tessellation language (STL) file format for further evaluation. For all three scanning methods, the largest absolute distance deviation occurred over the cross-arch span (249 \(\upmu\)m in group M, 190 \(\upmu\)m in group B, and 238 \(\upmu\)m in group P). The comparison between group B and group P regarding their average absolute distance deviation revealed a slight tendency in favor of group P. However, the difference between both groups was not statistically significant (\(p>0.05\)). Moreover, while the mean spread of the distance deviations for all other distances and all scanning methods was approximately in the same range, the mean spread for the cross-arch distance (P1-P2) was lower in groups B and P than in group M. No significant difference was found between either group M and group B or group P, or between group B and group P (\(p>0.05\)), except for the distance between P2 and P3, for which group B and group P differed significantly (\(p=0.049\)). Regarding precision balls 4 and 5 and the distance between the center points of the precision balls, the absolute mean vertical distance deviation and the vertical distance deviation mean spread were lower in group B and group P than in group M. Scanning with an artificial landmark reduced the mean absolute vertical distance deviations by 41% in group B and 50% in group P for precision ball 4 and by 47% in group B and 10% in group P for precision ball 5 compared with scanning using the manufacturer's strategy.