## 1 Introduction  
Since the introduction of CAD/CAM in 1980s, digitized databases have been used in various ways in different fields of dentistry because of their advantages in storing, sharing, and modifying available information [1; 2; 3; 4; 5]. In addition to active research on restorative dentistry and implantology, [PERSON] et al. [6] developed a computer-assisted marginal and internal fit of restoration [2; 7], [PERSON] et al. [3] analyzed the amount of tooth movement after extraction, [PERSON] et al. [4] fabricated orthodontic appliances, and [PERSON] et al. [8] introduced methods to utilize orthodontic diagnosis and treatment planning based on space analysis using digital dental models. Although most of the images were previously obtained from plaster models that were scanned extraorally [1; 3; 4; 9], multiple comparison studies have proved that digitized models demonstrate equal accuracy [8; 10; 11; 12]. Some studies that evaluated the accuracy of several direct intraoral scanning devices [4; 13; 14; 15; 16; 17] are also available. The notion of accuracy consists of trueness and precision (ISO 5725-1) [18]. Trueness represents the degree of sameness between the scanned image and the actual model without three-dimensional distortions. Precision is interchangeable with \"reproducibility\", which indicates the level of agreement between the images obtained in an equal environment. [PERSON] et al. [19] evaluated the mean deviation of iTero(r) at 50 \(\upmu\)m, to study the reproducibility of intraoral scanners. According to [PERSON] [20], direct measurements from the digital calipers on the experiment models can be compared with values obtained from scanned images. However, there is a potential limitation due to the likelihood of error derived from repeated measurements; thus, a reference scanner is required to prove the accuracy of experimental intraoral scanners. Experimental research was conducted with extraoral reference scanner D250 (3 Shape A/S, Copenhagen, Denmark) and D101 (Imetric 3D GmbH, Courgenay, Switzerland) in [PERSON] et al. [7] and [PERSON] et al. [17], respectively. Likewise, the industrial scanner, Sensable S3 (Solutionix Inc., Seoul, Korea), was selected as a reference scanner after its reliability was confirmed. This reference scanner uses the triangulation method to construct an image from acquired image information from multiple cameras based on reflections, as the subject is oriented to new positions at a consistent angle. Intraoral scanners such as iTero(r) and Trios(r) presented the potential for improved accuracy compared to other devices that use the confocal method, which limits their information to the use of in-focus reflected light. The purpose of this study was to evaluate the applicability of intraoral scanners in orthodontics by assessing the accuracy of scanning the full mandibular arch based on image comparison analysis report of sectioned versus full arch in [PERSON] et al. [21]. Our study also aimed to expand on previous knowledge at comparably lower accuracy found at the distal surface of the molar and the incisal edge of the incisor, by evaluating a well-aligned dental arch [17; 19; 22]. In this experiment, mandibular arch models with misaligned dentition requiring orthodontic treatment were used. Four interdentally spaced lower incisors had been misinterpreted as two, three, or even five teeth. Thus, deviations from measurements were calculated: (1) to assess the effects of anterior interdental space on the accuracy of intraoral scanners; (2) to measure changes in the accuracy of three-dimensional images based on different anterior interdental spaces and the type of scanner by comparing the scanned images with the reference image; and (3) to evaluate the effects on interdular width, which is a particularly significant clinical data.