## 4 Discussion
### Artificial Landmarks to Improve the Accuracy of IOSs  
In 2016, [PERSON] et al. were the first to publish an in vitro study discussing the accuracy of digital intraoral scans associated with artificial landmarks [28]. In this study, they compared the accuracy of three different IOSs (CS3500; Carestream Dental, Cerec Omnicam; Sirona, Trios; 3 Shape A/S) in an experiment which involved scanning a mandibular Dentiform model containing four prepared teeth and a 26-mm-long dertulous area. The model was first scanned without landmarks and after placing a 4 \(\times\) 3 mm alumina marker (Alumina marker; Dio implant Co, Busan, 612-020, Korea). For standardization, datasets from each scan were converted to stereolithography (STL) file format. The obtained datasets were used to evaluate trueness and precision. To compare the precision and trueness measurements, the obtained STL data were superimposed using reverse engineering software (Rapidform 2006; INUS Technology Inc., Seoul, Korea). Without the use of an artificial landmark in the edentulous ridge, it took more time and more images to register the scan. Scans were performed successfully by all scanners except the Cerec Omnicam, which had stitching issues. The scans of all three IOSs were successful and faster when the artificial landmark was placed on the edentulous ridge. Without an artificial landmark on the edentulous area, the mean trueness for the TR was 36.1 \(\pm\) 7.0 \(\upmu\)m and 38.8 \(\pm\) 17.5 \(\upmu\)m for the CS. The mean trueness for the OM could not be obtained because of a scanning failure. With the presence of an artificial landmark on the edentulous area, the mean trueness for the TR was 30.6 \(\pm\) 3.6 \(\upmu\)m and 26.7 \(\pm\) 3.5 \(\upmu\)m for the CS. The mean trueness was not significantly different. The mean trueness for the OM, meanwhile, was 31.8 \(\pm\) 5.4 \(\upmu\)m. The results of this study showed a dramatic increase in precision when the artificial landmark was placed, whereas trueness showed no differences with or without the artificial landmark. Without a \begin{table}
\begin{tabular}{c c c c} \hline
**References** & **Study Type** & **Intraoral Scanner Used** & **Conclusions** \\ \hline [PERSON] et al. [33] & In vitro study & 3 Shape Trios 3 & When covering the edentulous ridges with AGP, there was a significant improvement \\  & & Itero Element 1 & in both trueness and precision \\ \hline [PERSON] et al. [34] & In vitro study & 3 Shape Trios 3 & Auxiliary devices have significantly improved IOS scanning accuracy in complete-arch implant scanning \\ \hline \end{tabular}
\end{table} 
Table 2: Use of auxiliary geometry part (AGP) to improve the accuracy of IOSs. \begin{table}
\begin{tabular}{c c c} \hline
\begin{tabular}{c} **Conclusions** \\ \end{tabular} \\ \hline \end{tabular}
\end{table} 
Table 3: Splinting ISBs to improve the accuracy of IOSs. marker on the dedentulous space, the mean precision for the TR was \(13.0\pm 4.2\)\(\upmu\)m. However, the mean precision for the CS was 43.6 \(\pm\) 23.4 mm. In contrast, with an artificial landmark placed on the dedentulous space, the mean precision improved significantly (\(p<0.001\)). For the TR, it was 9.2 \(\pm\) 2.3 \(\upmu\)m; for the CS, it was 12.4 \(\pm\) 2.3 \(\upmu\)m. For the OM, the mean precision was \(10.5\pm 2.6\)\(\upmu\)m. This study shows how it was possible to acquire an accurate and reliable scan when an artificial landmark was used in the long dedentulous area of the study model [28]. In a recent review, [PERSON] et al. [37] reported that, currently, the intraoral scanner is widely used with encouraging results, both functional and aesthetic, for the fabrication of individualized CAD/CAM and 3D printing meshes for implant and prosthetic rehabilitation in patients with vertical and mixed (vertical and horizontal) bone defects. In 2020, [PERSON] et al.