## 4 Discussion
### Artificial Landmarks to Improve the Accuracy of IOSs
This study proved that the use of an artificial landmark in the dorsal palate can significantly improve the scanning accuracy and reliability of vertical distance deviations [31]. [PERSON] et al., in their 2021 study, investigated the digital scanning accuracy of partially and completely edentulous jaws using five different IOSs with and without additional artificial landmarks [32]. The IOSs evaluated were Primescan (Dentsply Sirona), TRIOS 3 (3 Shape), TRIOS 4 (3 Shape), Carestream 3600 (Carestream dental), and Medit i500 (Medit). Two maxillary models were made: one model was missing the right premolars and molars, and dental implants (BLT Implant, \(\O\) 4.1, Straumann AG) were inserted to replace them. The second model was completely dedutulous, and four implants were inserted. The artificial landmark used was a polymerized glass-ionomer cement (Fuji Plus; GC) that was attached using an adhesive (Super Moment glue; Henkel). One was attached in the center of the edentulous area of the partially edentulous model, six in the completely edentulous model distributed between the ISBs, and three in the palate of the completely edentulous model. The results show that, for the distance measurements, the mean trueness values ranged from \(-\)46.7 \(\pm\) 15.4 \(\upmu\)m for the TRIOS 3 scanner to 392.1 \(\pm\) 314.3 \(\upmu\)m for the Medit i500 scanner in models without an additional artificial landmark; however, in models with additional artificial landmarks, the mean trueness of distance values ranged from \(-\)34.4 \(\pm\) 13.0 \(\upmu\)m for the TRIOS 4 IOS to 117.7 \(\pm\) 232.3 \(\upmu\)m for the CARESTREAM 3600 IOS. Mean trueness values of angulation varied from \(-\)0.0 \(\pm\) 0.5 degrees for the CARESTREAM 3600 IOS to 0.2 \(\pm\) 0.0 degrees for the PRIMESCAN IOS in models without additional artificial landmarks. Meanwhile, in models with artificial landmarks, the mean trueness values of angulation ranged from 0.0 \(\pm\) 0.2 degrees for the TRIOS 3 IOS to 0.4 \(\pm\) 0.5 degrees for the CARESTREAM 3600 IOS. For the vertical shift measurements in models without additional artificial landmarks, trueness varied from \(-\)108 \(\pm\) 47.1 \(\upmu\)m for the TRIOS 4 IOS to 107.2 \(\pm\) 103.5 \(\upmu\)m for the Medit i500 IOS. The mean trueness values of vertical shift in models with additional artificial landmarks ranged from \(-\)15 \(\pm\) 45 \(\upmu\)m of CARESTREAM 3600 IOS to \(-\)86.9 \(\pm\) 42.1 \(\upmu\)m. No statistically significant differences were found between the measurements of the models with or without additional artificial landmarks, except for the Medit i500 IOS in all parameters and PRIMESCAN in the angle measurements (\(p\) \(<\) 0.05). Regarding the partial edentulous model, the best results were demonstrated by the TRIOS 3 IOS in distance (12.8 \(\pm\) 7.2 \(\upmu\)m) and PRIMESCAN in angulation (0.0 \(\pm\) 0.0 degrees) and vertical shift parameters (9 \(\pm\) 7.4 \(\upmu\)m). However, no statistically significant differences were found between the scans with and without additional artificial landmarks (\(p\) \(>\) 0.05) of any IOS tested, except Medit i500 in the distance and vertical shift parameters and CARESTREAM 3600 in vertical shift (\(p\) \(<\) 0.05). The precision and trueness of the digital scans of the completely edentulous areas were affected, except for the Medit i500 IOS for distance (\(p\) = 0.08, \(p\) = 0.07, and \(p\) = 0.36), PRIMESCAN (\(p\) = 0.75, \(p\) = 0.26, and \(p\) = 0.67), and TRIOS 4 (\(p\) = 0.76, \(p\) = 0.7, and \(p\) = 0.84) for angle, as well as all systems except TRIOS 4 (\(p\) = 0.49) for vertical shift precision. The results of this study showed that a limited effect of the additional artificial landmark was observed on the accuracy parameters when partially edentulous conditions were scanned, while the accuracy of completely edentulous arches improved when the additional artificial landmark technique was used.