## 4 Discussion  
In our study, the trueness and precision of both IOS and alginate impression measurements were not statistically different. We found that the trueness and precision of the alginate impressions in all groups ranged from 87-102 microns and 80-103 microns, respectively. [PERSON] et al. [18] showed that alginate impression accuracy ranged from 44-188 microns in full arch models without orthodontic brackets, whereas [PERSON] et al. [19] found that the mean precision of an alginate impression was 162.2 \(\pm\) 71.3 microns in the complete arch. Dimensional changes can be caused by water temperature, environment, water, or powder ratio. Nowadays, digital technology provides an alternative pathway of data acquisition in dental fields. Although IOS has many advantages such as ease of use, time saving, and improved patient satisfaction, its accuracy depends on its system and version [1]. This study demonstrated that the trueness and precision of intraoral scanners in all groups were 72-102 microns and 79-108 microns, respectively. Many studies have found that TRIOS(r) intraoral scanners have high accuracy. One study found that no statistically significant difference was recorded between four IOS systems (Trios(r), 3 Shape, CEREC Omnicam(r), and Sirona) [20]. [PERSON] et al. [21] studied the accuracy of intraoral scanners in complete arch maxillary models and found that accuracy (both trueness and precision) was as follows: CS 35001(r) (trueness 63.2 microns and precision 55.2 microns) > Trios(r) (trueness 71.6 microns and precision 67.0 microns) > Zfx Intracan(r) (trueness 103.0 microns and precision 112.4 microns) > Planscan(r) (trueness 253.4 microns and precision 204.2 microns). Moreover, [PERSON] et al. [11] studied the accuracy of intraoral scanners in complete arch models and found that the accuracy of 3M(r) and TRIOS(r) intraoral scanners was higher than that of OMNT(r). [PERSON] et al. [14] found that iTero and Trios had better trueness and precision than Zfx IntraScan(r) and E4 Dentist(r). [PERSON] and [PERSON] compared the accuracy of CS 3600(r) and TRIOS 3(r) intraoral scanners in full arch models and reported that TRIOS 3(r) had better precision than CS 3600(r), with the precision of around 20-70 microns [22]. In addition, [PERSON] et al. [23] studied the accuracy of several intraoral scanners (Trios 3(r), Trios 4(r), 1 Tero Element(r), and iTero Element(r), and iTero Element(r)). They concluded that the Trios(r) series showed the highest accuracy. TRIOS(r) may show particularly high accuracy because it is a confocal intraoral scanner. In this study, the selected areas of STL files were all just above the reference markers. As the surgical splint used in orthognathic surgery must attach to the occlusal surfaces of teeth and areas around 3 mm from incisional or occlusal surfaces of teeth, we applied the reference markers at 3 mm below the incisional or occlusal of teeth and cut STL files above them. [PERSON] et al. [19] found that IOS systems had higher levels of deviation in local areas than alginate impressions. The errors of intraoral scanners often occurred at posterior teeth and palatal areas of anterior teeth [22]. Furthermore, local deviations along the palatal surfaces of the molars and incisional edges of the anterior teeth were less than 100 microns [11; 20].