## 2 Materials and Methods  
### Case Report  
A 20-year-old Japanese man presented with a chief complaint of the crowding of his anterior teeth. His pretreatment facial profile was straight with a mild retrusive upper lip that receded the E-line, and a mild protruded lower lip that exceeded the E-line (Figure 1). The frontal view was almost symmetrical, and the maxillary and mandibular dental midline almost coincided with the facial midline. When smiling, the gums were mildly exposed. Model analysis revealed Class I molar and Class II canine relationships on both sides, an overjet of 3.8 mm, an overbite of 5.3 mm, arch length discrepancies of \(-3.5\) mm on the maxillary arch and \(-5.5\) mm on the mandibular arch, a narrow maxilla, and buccal inclination of the maxillary second molars due to the posterior crowding. The maxillary third molars on both sides had erupted. The mandibular incisors had protruded, and a Spee curve was observed. The anterior tooth size ratio indicated that the size of the mandibular anterior teeth was slightly larger than that of the maxilla (Figure 2). Before treatment, panoramic and lateral cephalometric radiographs were obtained for diagnosis (Figure 3). The lateral cephalometric radiographs revealed the end of the skeletal growth period according to the cervical vertebral maturation, indicating that the patient was an adult [17]. Panoramic radiography revealed bilateral horizontally impacted third molars in the mandible, a mesial inclination of mandibular molars, and a maxillary sinus floor located inferiorly and close to the roots of the maxillary molars. After the panoramic radiography, CBCT was performed for a more detailed anatomical examination to extract the maxillary and mandibular third molars. The CBCT findings revealed that several roots of the maxillary molars protruded into the maxillary sinus (Figure 4). The cephalometric analysis (Table 1), compared with the Japanese norm, showed a skeletal Class I relationship (ANB angle, \(3.5^{\circ}\)). The mandibular plane was large (FMA, \(32.4^{\circ}\)). The maxillary incisor was labially inclined (U1 to FH, \(116.5^{\circ}\)), whereas the inclination of the mandibular incisors was within the normal range (FMIA, \(56.0^{\circ}\)). Figure 1: Pretreatment facial and intraoral photographs. Figure 2: Pretreatment dental casts. Figure 4: Pretreatment cone-beam computed tomography (CBCT) images of the relationships between the maxillary molars and the maxillary sinus. (**A**) Axial image; (**B**) coronal image; (**C**) sagittal image simultaneously. Abbreviation: MS, maxillary sinus. Figure 3: Pretreatment lateral cephalometric, cephalometric tracing, and panoramic radiographs. The treatment objectives were to (1) reduce the crowding, (2) establish a satisfactory occlusion with stable anterior and posterior supports, (3) establish the relationship between the Class I molar and canine on both sides, (4) align the maxillary incisors with the appropriate axis, (5) improve the patient's previously gum-revealing smile, and (6) induce appropriate overbite and overjet. To eliminate crowding and achieve Class I occlusion, distalization of the maxillary molars and making the mandibular molars upright were necessary. To distally move these molars, it was necessary to extract the maxillary and mandibular third molars because distal spacing with cancellous bone was required. TADs (Dualtop; Jeil Medical, Seoul, Korea) were used to achieve anchorage for the intrusion of the maxillary anterior teeth and distalization of the maxillary molars. The following alternative treatment was presented to the patient: To eliminate the crowding of the incisors, we considered extracting the premolars. However, in the diagnostic setup model with the extraction of the maxillary premolars, the amount of movement of the maxillary molars through the maxillary sinus increased compared with the distalization of the maxillary molars without premolars extraction.