## 4 Discussion  
This study compared the trueness of digital implant impressions according to the ISB orientation and scanning method in the cases of a single implant in the presence of adjacent teeth. For two of the three intraoral scanners, there were significant differences according to the ISB orientation and the scanning method. For the tabletop scanner, it was found to show higher trueness to connect the ISB with its flat surface facing the buccal direction; that is, the null hypothesis of this study was partially rejected for three types of intraoral scanner, and rejected for one laboratory scanner. For the prealignment data, the overall RMSE was significantly lower in the buccal group than in the proximal group for the three intraoral scanners. Deep, undercut, angled, inclined, or crowded surfaces of surrounding structures are difficult to scan and hence cause inaccurate point clouds, which may decrease the scan accuracy in proximal areas [28; 29]. This difference in ease of scanning between the buccal and proximal surfaces would have influenced the trueness according to the ISB orientation. For the postalignment data, the RMSE was lower when the flat surface of the ISB faced the buccal direction and a full scan was performed. The effects of the ISB orientation and scanning method do not seem to be completely compensated for even in the process of  
Figure 8: The postalignment data in which the virtual abutments were created by aligning using the implant library, and the trueness was evaluated by superimposing the reference scan data and extracting the abutment areas. The deviation tended to be lower in the buccal groups than in the proximal groups, and lower in the full-scan groups than in the partial-scan groups. The deviation tended to decrease relative to the prealignment data: (**A**) buccal–full group, (**B**) buccal–partial group, (**C**) proximal–full group, and (**D**) proximal–partial group. Figure 7: After connecting the ISB, scanning procedures were performed to obtain prealignment data, and the trueness was evaluated by superimposing the reference scan data and extracting the ISB areas. The deviation tended to be lower in the buccal groups than in the proximal groups, and lower in the full-scan groups than in the partial-scan groups: (**A**) buccal–full group, (**B**) buccal–partial group, (**C**) proximal–full group, and (**D**) proximal–partial group. aligning with a virtual implant, which seems to have a subtle effect on the completion of the process of aligning library data. In the case of fabricating restorations from natural teeth, it is important to capture the details of the teeth well, including in the margin area. However, in the case of implants, only the location of the ISB is important, resulting in differences in the reported importance of the scanning method [30]. However, the present study confirmed that a meticulous full scan of the entire areas of the ISBs is important even when scanning an implant case using ISBs. This is consistent with the finding of [PERSON] et al. that the imaging deficiency of the ISB influenced the position of the virtual implant; these authors suggested that a surface area deficiency of more than 10% in an ISB should be avoided [24]. The present study found that both prealignment and postalignment data showed differences in RMSE values according to the ISB orientation and scanning method for different scanners. For the implant, after data are acquired by scanning, mesh reconstruction is performed using an implant library, and a virtual implant is created by surface matching with the digital implant library [9]. Therefore, not only the scan quality but also the shape-matching algorithm affect the accuracy. The differences in trueness according to scanner types in the present study may have resulted from not only the scanning process itself but also during data processing.