## 4 Discussion
\begin{table}
\begin{tabular}{l c c c c c c c c c c c c c} \hline \hline
**Superimposition** & **Figure 13D** & \multicolumn{8}{c}{**Figure 13H**} & \multicolumn{8}{c}{**Figure 13L**} \\ \hline Tooth & 6C & 7C & 6 MB & 6 DB & 6P & 7 MB & 7 DB & 7P & 6 MB & 6 DB & 6P & 7 MB & 7 DB & 7P \\ \hline Right side & & & & & & & & & & & & & \\ \hline Distal movement (mm) & 2.06 & 3.01 & 2.12 & 2.25 & 0.76 & 2.42 & 3.10 & 2.91 & 1.49 & 2.28 & 0.48 & 3.08 & 3.19 & 1.96 \\ Palatal movement (mm) & \(-\)1.97 & 2.67 & 0.31 & 0.35 & 0.46 & 1.14 & 1.56 & 2.07 & 0.47 & 0.92 & 0.49 & 0.53 & 1.55 & 1.63 \\ \hline Left side & & & & & & & & & & & & & & \\ \hline Distal movement (mm) & 2.23 & 2.61 & 2.58 & 2.35 & 0.46 & 2.49 & 2.78 & 2.23 & UM & UM & UM & UM & UM \\ Palatal movement (mm) & \(-\)1.15 & 2.80 & 0.88 & 1.56 & 0.34 & 0.94 & 1.24 & 1.80 & UM & UM & UM & UM & UM \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Distal and palatal movement of the maxillary first and second molars measured with superimposed CBCT images. through the maxillary sinus. Alveolar bone remodeling was visible around the roots after moving through the maxillary sinus. In general, the evaluation of orthodontic treatment has been performed using panoramic and cephalometric radiographs. Although these radiographs are widely available and allow visualization of the various anatomic structures at low doses of radiation [30], they lack 3D information [14; 30]. CBCT images overcome these limitations by providing multiplanar images in three dimensions with high spatial resolution [15]. In particular, an evaluation of the movement in coronal and bucco-palatal directions is considered useful because it cannot be obtained using the 2D images from lateral cephalometric radiographs. In addition, it can visually confirm the bodily movement of the maxillary teeth through the maxillary sinus in the pre- and post-treatment CBCT superimposition. This is one of the few reports of distal movement of the maxillary molars through the maxillary sinus [8] and the first report of orthodontic bodily movement in the palatal direction. To the best of our knowledge, this is the first report of the evaluation of palatal root movement through the maxillary sinus. According to a cross-sectional study [20], the proportion of the palatal roots protruding into the maxillary sinus showed a high probability. However, even in previous studies in which the tooth moved through the maxillary sinus [4; 9; 13; 24], the movement of the mesial and distal buccal roots of the molars could be confirmed, but the movement of the palatal roots was not evaluated. In other words, the movement of the molars was not accurately understood. Therefore, the accurate evaluation of the palatal root movement can provide useful information for clinicians. As reported in the results, the pre- and post-treatment CBCT images were helpful for diagnosis and evaluation of treatment. However, cases need to be cautiously selected because using CBCT is associated with radiation exposure. CT imaging should be performed for safety when several roots seem to protrude to the maxillary sinus according to the 2D radiographs. There is a high possibility of root resorption during 3D tooth movement, such as molar intrusion to the maxillary sinus or mesio-distal and bucco-palatal directional movement through the maxillary sinus [11; 12]. The degree of intrusion through the maxillary sinus can affect the difficulty of orthodontic treatment [20; 31]. Therefore, knowledge of the proximity of the maxillary root apices to the sinus floor is important for the safe delivery of orthodontic treatment and the prevention of any associated problems.