## 4 Discussion
Hence, it was hard to determine the effect of the accuracy of the scan data from IOS on the VIR. [PERSON] et al. assessed the VIR in the full arch scan of the varying edentulous conditions [13]. Although the full arch scan data were obtained from the IOS, there was a lack of information about the distortion in scan data. In the study of [PERSON] et al., the mean difference of interarch marker distance was 60 \(\upmu\)m in the complete dentate full arch and 870 \(\upmu\)m in the full arch with extended edentulous span. In our study, the median unsigned difference of interarch marker distance was 10.5 \(\upmu\)m in the FPS group of Trios and 386.3 \(\upmu\)m in the LSDEB group of i500. Comparing the results of our study, the errors in VIR were reduced in the quadrant arch scan. However, a previous study, which was done in the quadrant arch, showed comparable results. In the study of [PERSON] et al., the total translation of the VIR in a complete dentate quadrant arch was at 66.6 \(\upmu\)m in Trios 3 [9]. In our study, the median unsigned difference of the FPS group in the Trios3 ranged from 10.5 \(\upmu\)m in position 3 to 31.2 \(\upmu\)m in position 7. Considering the differences between measuring methods in studies, the results of our study were comparable to those of [PERSON] et al. The results of this study showed that the registration of the occlusal relationship using IOSs in the edentulous area with more than two missing teeth might be clinically more inaccurate than that obtained with a laboratory scanner [12; 13]. In this situation, it is recommended to apply a digital workflow including a laboratory scanner. If clinicians want to use IOSs, it is recommended to use an additional scanning strategy such as markers on the missing area for improved clinical results [13]. In addition, it might be necessary to compensate for the distortion of the occlusal relationship during the CAD or milling process [1; 12]. Clinicians should be aware that there are differences in the characteristics between IOSs in the registration of interoclusal relationships, especially when edentulous areas exist. There are differences in the accuracy of scans for each IOS [3; 16] and in the algorithm for post-processing scan data [6]. Additionally, the accuracy of the scan differs according to the edentulous condition [16; 21], and the discrepancy may vary with VIRs [11; 12; 14]. In our study, depending on the edentulous condition and the type of IOS, there were local or general deviations in the occlusion of the experimental groups compared to laboratory scanner. In some groups, a tilting effect occurred in the posterior regions. If excessive occlusal adjustment or additional repair is expected during the try-in procedure of the prosthesis due to unacceptable occlusal registration, the digital workflow using an IOS may not be predictable [8]. This study had limitations because it was not able to reproduce all clinical scenarios. In addition, being an in vitro study, it was not possible to reflect various clinical environments that could affect the accuracy of the scan images and the VIR, such as saliva, soft tissue, patient movement during scanning, and restriction of the scanner tip in the oral cavity [13; 22; 23]. This study evaluated the VIR in the edentulous region without structures that the IOS can recognize. Clinically, the presence of an implant scan body, healing abutment, or abutment tooth may affect the scan image and VIR. In future studies, the relationship between the presence of recognizable the structure and the accuracy of the VIR needs to be conducted. Furthermore, additional research with a larger number of specimens is necessary to establish a fully digital workflow using an IOS that minimizes the possibility of occlusal adjustment.