## 4 Discussion  
The results of this study showed a significant difference in the accuracy of the eight types of scanners (\(P<0.001\)), and there was a significant difference according to the type of tooth and the anterior and posterior regions (\(P<0.001\)) (Tables 1-3). Thus, both the null hypotheses of the study were rejected. The accuracy of the scanner cannot be confirmed only by the comparison of the overall accuracy of the maxilla and mandible. During the process of creating virtual models with the scanners, the 3D displacement may occur, and the mean value of the distance of all point clouds cannot represent the error in a specific part [3]. Thus, in this study, each tooth was divided to examine the accuracy of  
Figure 6: Comparison of the color difference map according to the scanner. (**A**) 3 shape E1. (**B**), degree of freedom (DOF). (**C**) CS3500. (**D**) CS3600. (**E**) Trios2. (**F**) Trios3. (**G**) i500. each tooth, the anterior region, and the posterior region separately. Forming a virtual plane, this study examined the planar displacement value (Tables 1-3). This study showed a significant difference in the accuracy according to the anterior and posterior regions in all eight scanners (Table 2). Previous studies showed a difference in the accuracy according to the size and shape of the object scanned [2,19]. The accuracy was found to be poor in the posterior region in this study, suggesting that the manufacturer should improve this. Also, the findings of this study regarding accuracy could provide important information for developing a more improved intraoral scanner. In numerous previous studies, poor accuracy was found to adversely affect the fit of fixed prosthesis [12,20]. The scanning data plays the most essential role to produce prostheses and poor scanning accuracy provides the prostheses with a bad fit for patients [20,21]. The previous studies evaluated the accuracy of the scanning data based on 100 \(\upmu\)m [3,9,18]. Therefore, this study concluded that three types of intraoral scanners (CS3500, CS3600 and Trios3) could be recommended for scanning of the complete arch, whereas two other types of intraoral scanners (Trios2 and i500) could not be recommended. This study is significant in that the overall accuracy of the Trios2 Group (\(92.8\pm 32.7\)\(\upmu\)m) was within the range of the clinically allowable scanning accuracy (<100 \(\upmu\)m); however, it is difficult to consider it to be within the clinically allowable range for complete arches in terms of horizontal displacement (\(112.3\pm 50.9\)\(\upmu\)m) in the virtual plane. The scanning accuracy of the left 2 nd molar in the CS3500 Group (\(126.8\pm 51.6\)\(\upmu\)m) deviated from the allowable range, but the overall accuracy (\(62.4\pm 19.8\)\(\upmu\)m) and the horizontal displacement (\(56.5\pm 25.5\)\(\upmu\)m) were within the range of accuracy for a complete arch. In conclusion, it is difficult to recommend intraoral scanners for use based only on the comparison of the overall accuracy, which were evaluated in previous studies. Thus, in the results of this study, it would also be necessary to evaluate the horizontal displacement and the scanning accuracy of each tooth in addition to the 3D evaluation method. Many previous studies have evaluated the accuracy of a complete arch using intraoral scanners. In the studies by [PERSON] et al. [3], the accuracy of complete arch using intraoral scanner of Trios 2, Trios 3, CS3500, and CS3600 showed \(343.4\pm 56.4\)\(\upmu\)m, \(183.9\pm 49.7\)\(\upmu\)m, \(209.9\pm 53.7\)\(\upmu\)m, and \(118.9\pm 42.1\)\(\upmu\)m, respectively. The reason for the poor accuracy compared to the results of this presented study is due to the difference in the alignment method between CRM and CTM. The alignment method by [PERSON] et al. confirmed the distortion of the arch by aligning only the teeth at which the scan begins [3], but in this presented study, the accuracy of the entire arch was determined by aligning all the scanned teeth. In the studies by [PERSON] et al.