## 4 Discussion  
Evaluating the accuracy of intraoral scanners has become an important topic of research in clinical orthodontics, since digital models can be applied to many areas of orthodontic diagnosis and treatment. While the accuracy of intraoral scanners has been studied in many literatures with respect to ideal occlusion and teeth alignment, such optimal situations are not always the case in orthodontic patients. Therefore, in this study, we aimed to assess the accuracy of scanning the full mandibular arch when there were various distances of interdental spaces present in the mandibular incisor region. Our results indicated that the increase in the interdental space among the lower incisors led to a significant deviation in the molar region. The deviation was produced because the size of the scanner's sensor was confined to certain dimensions. Therefore, a complete three-dimensional image of the entire \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Model**} & \multicolumn{2}{c}{**iTero®**} & \multicolumn{2}{c}{**Trios®**} & \multirow{2}{*}{_p-Value_} \\ \cline{2-3} \cline{5-5}  & **Mean (SD)** & **Mean (SD)** & \\ \hline Ideal & 0.20 (0.01) & 0.02 (0.02) & \textless{}0.001 * \\ Mild & 0.17 (0.08) & 0.07 (0.03) & 0.112 \\ Moderate & 0.11 (0.03) & 0.22 (0.02) & 0.004 * \\ Severe & 0.38 (0.01) & 0.04 (0.03) & \textless{}0.001 * \\ \hline \hline \end{tabular}  
* Indicates that the values are statistically different between iTero® and Trios® (_p_ \textless{}0.05). Ideal presents the ideal arch dentiti; Mild 1 mm spacing dentiti; Moderate 3 mm spacing dentiti and Severe 5 mm spacing dentiti. Mean value of iTero® is the average intermid width when the data was scanned 10 times using iTero; Mean value of Trios® is the average intermid width when the data was scanned 10 times using Trios®. SD: standard deviation.  
\end{table} 
Table 7: Comparison of differences in interolar widths in iTero® versus Trios® (unit: \(\upmu\  
arch was obtained by an image assembly process, called stitching. This method involves attaching the overlapped areas created by two adjacent images, but is prone to deliver inaccurate information when similar overlapping patterns repeat in the stitching area [21]. Because there were overlapped areas with similar repeated patterns in the mandibular incisor region of the scanned images, the errors created in the stitching process led to deviations in the molar region. With iTero(r), an undesired overlapped area from one canine to the contralateral canine was produced when the left and right sides of the arch were scanned separately and then combined in the anterior region. This slight error created when superimposing the left and right sides appeared more exaggerated in the molar region. However, Trios(r) also produced deformations when the models were scanned from the most distal molar to the contralateral molar, despite scanning the anterior incisor region slowly in a zigzag pattern, from lingual to buccal. For Trios(r), the accumulated errors were most evident on the contralateral side. Even though the interdental space was increased without altering other factors (such as intermolar width, incisor angulation, and torque), elongation of the incisor region due to the increase in interdental space caused lengthening of the arch, which, in turn, caused deformation in the molar area. Figure 7 shows deviations in the superimposed images of the models when the images were scanned using iTero(r). other removable appliances. The deviations found among individual teeth may also produce defects in making transfer zig for indirect bonding. It is important to note that determining whether the value of deviation is small or large is subjective. The amount of deviation that affects the clinical outcome depends on the purpose of taking digital impressions; the objective is similar to that of taking conventional impressions.