## 4 Discussion
### Artificial Landmarks to Improve the Accuracy of IOSs
analyzed the accuracy and scan time using the TRIOS (3 Shape) IOS, combined with four different intraoral scan techniques: unmodified master model (NO), glass fiduciary markers placed on the dedentulous ridge (GB), pressure-indicating paste brushed over the ridge and palate (PP), and floss tied between the scan bodies (FL), as well as five different commercially available ISB systems: Atlantis I-Flo (AF), Core3D (C3D), Nt-Trading (NT), Dess-USA (DE), and Zimmer Biomet (ZI) [29]. Five dedentulous models with four parallel dental implant analogs (TSV 4.1; Zimmer Biomet Dental) were used for the study. This is the first work to include different intraoral scanning techniques and different ISBs in the study of dedentulous patients. Regarding distance deviation, ZI showed significantly less distance deviation than AF (\(p=0.041\)), and FL showed significantly more distance deviation than GB (\(p=0.008\)), PP (\(p=0.013\)), and NO (\(p=0.002\)). A significant difference in precision regarding distance deviation was noted from the tests conducted to assess the homogeneity of the variances (\(p=0.013\)). In terms of angular deviation, a significant difference in precision was also noted for the angular deviation (\(p=0.003\)), with the subgroup AS-FL being significantly less precise than both ZI-GB (\(p=0.021\)) and ZI-PP (\(p=0.022\)). Regarding scan time, simple main effect analysis demonstrated a statistically significant difference in the means of the scan time between the following scan bodies: C3D and NT (\(p=0.004\)), DE and ZI (\(p=0.017\)), and NT and ZI (\(p<0.001\)). The mean scan times were significantly lower for the ZI group (2.11 min) than for the DE (2.54 min) and NT (2.77 min) groups, and the mean scan time for the C3D group (2.19 min) was significantly lower than that for the NT group (2.77 min). The results of this study suggest that ISBs by themselves could affect the accuracy of the scan. The Zimmer Biomet scan body had significantly less distance deviation, whereas splinting scan bodies with floss led to significantly more distance deviation. The scan time was significantly different depending on the type of ISBs used. Regarding the scanning techniques, those involving a modification of the tissue surface did not show an improvement in accuracy when compared with the techniques where the surface was not modified [29]. In 2022, [PERSON] et al. compared the effects of artificial landmarks and three different scanning patterns (linguo-buccal pattern--LB, S-shaped pattern--SS, and quadrant pattern--QP) on the accuracy of the complete-arch implant intraoral digital scans using and IOS (Trios\({}^{\circledR}\), 3 Shape) [29]. For this study, they used an dedentulous mandibular model with four dental implant analogs (GSTLA400, Ostsem Implant Co., Avegno, Italy). Three different artificial landmarks were used to modify this model: pressure-indicating paste (3 mm \(\times\) 2 mm) brushed over the ridge (PIP), liquid dam markers (3 mm in diameter) placed on the dedentulous ridge (LD), and floss tied with pattern resin (9 mm \(\times\) 3 mm \(\times\) 2 mm) between the scan bodies (FL). As shown by this study [30], artificial landmarks and scanning patterns have a significant effect on the trueness of the scans. The artificial landmark was used to enhance the registration of the dedentulous ridge. The artificial landmark was proposed as an indicator to improve the readability of the tissue. This is in agreement with [PERSON] et al., who reported that the accuracy of intraoral scans was improved if an artificial landmark in the long dedentulous span was used [28]. Artificial landmarks and scanning patterns affected the root mean square (RMS) values of trueness. In each artificial landmark group, QU scanning patterns were found to have the lowestRMS values of trueness (all \(p<0.05\)).