## 4 Discussion
For example, if the goal of taking digital impressions was to reach the level of accuracy of taking alginate impressions (i.e., for orthodontic diagnosis or fabrication of removable orthodontic appliances), there would be clinical errors in reproducibility if the range of error was greater than 0.2 mm. For reference, the range of error in the alginate impression technique is reported to be up to 0.18 mm [24]. If the aim was to achieve the level of accuracy of taking rubber impressions (i.e., for restorations or making zig for precise indirect bonding), there would be clinical errors in reproducibility if the range of error was greater than 0.05 mm. Upon comparing the accuracy of the two scanners, however, Trios(r) showed a greater accuracy than iTero(r) in all sections, with more prominent differences between the left and right molar regions. The highest deviation in the interpolar width of the Moderate model was greater by 0.66 mm with iTero(r) and was smaller by 0.76 mm with Trios(r). Differences in the interpolar width deviations, as shown in Figure 11, were due to uniformly distinct superimposed data seen with iTero(r) toward the molars in the scanned image compared to the reference image. In Trios(r), there was an unequal mixture of expanded and constricted portions in the scanned images, which explained the corresponding expansion and constriction of interpolar width. Intermolar width provides important information in data-based treatment planning and construction of orthodontic appliances. Our results indicated that due to a large deviation in interpolar width (the highest deviation value was 0.7 mm), iTero(r) may not be suitable for making orthodontic appliances for the mandibular teeth with large anterior interdental spaces. Such an undesired phenomenon with iTero(r) parallels the findings in [PERSON] et al. [17], where horizontal expansion of molar region was observed during the process of image integration through the software within the scanner. These observations, however, contradict the statements from [PERSON] et al. [19] in that digital models made with iTero(r) can be used for treatment planning and making orthodontic appliances, and from [PERSON] et al. [25], which supports the use of three-dimensional laser scanning for treatment changes, growth, surgical stimulation, and fabrication of orthodontic appliances. Yet, it is important to note that interdental spaces in the anterior region and the subsequent interpolar width deviations in this study suggest potential limitations of the clinical use of iTero(r) in orthodontic settings. Overall, this study showed that the accuracy of scanned images was correlated to the increase in anterior interdental spaces of the lower arch, affecting the extent of the clinical use of intraoral scanners in orthodontics. More errors were found in the incisor area due to uniformity in the shape of incisors, and more distinct results were found in the Severe model, which represented the lower arch with atypical tooth arrangement. The accuracy of the experimental intraoral scanners may be reduced  
Figure 11: Deviation occurs in the posterior area after superimposition. Blue: data from the intraoral scanners, Trios® and iTero®; Green: data from the reference scanner. (**A**) Represents iTero®: more blue than green in the posterior region. (**B**) Represents Trios®: mixed blue and green in the posterior region. if there are similar patterns of spacing repeated among the mandibular incisors. These factors should be acknowledged when using the scanners. In addition, because the scanners were applied to dry, powdered models, different measurements were expected when the scanners were used directly with patients. For the purpose of this study, patient-related factors (such as patient movement, limited intraoral space, oral humidity, and saliva flow) were disregarded [19].