## 4 Discussion
To assess the stability of maxillary and mandibular total arch distalization, we used pretreatment (T0), post-treatment (T1), and posttrention (T2) lateral cephalometric radiographs and dental casts. The use of dental casts along with lateral cephalometric radiographs enabled evaluation of both transverse dental changes and anteroposterior movements. The subjects of this study were patients who were treated with total arch distalization using TADs, i.e., distalization of the anterior and posterior parts of dentition as one unit using TADs. T1 lateral cephalometric radiographs and dental casts revealed statistically significant distalization of both incisors and molars. The maxillary and mandibular first molars were distalized by 2.46 and 2.60 mm on average, respectively, which are lower results than those yielded in the study of [PERSON] et al. and similar to those reported by [PERSON] et al., who conducted total arch distalization using the same method [26; 27]. These interstudy differences may be ascribed to the different treatment goals depending on the severity of anterior crowding and the degree of required correction of the molar relationship. T2 lateral cephalometric radiographs and diagnostic casts revealed that all teeth underwent mesial drift during the retention period, whereby statistically significant mesial drift was observed in maxillary first molar crowns (mean 0.52 mm) and maxillary second molar crowns and roots (mean 0.65 and 0.58 mm, respectively). [PERSON] et al. reported that the mean mesial drift of mandibular molars was 0.3 mm (range: 0.0-1.0 mm) one year after mandibular molar distalization using miniplates [25]. [PERSON] and [PERSON] performed a long-term observational study of tooth movements in adults without orthodontic treatment and reported mesial drift, although statistically not significant, of maxillary molars (0.42 mm in women and 0.26 mm in men on average) and incisors (0.07 mm in women, 0.39 mm in men) [28]. These results are largely consistent with the mesial drifting tendency observed in this study, suggesting that postdistalization mesial drifting tendency does not exceed the mesial drifting tendency in untreated adults. One of the arguments advocating extraction treatment is that maxillary and mandibular molars cannot be distalized bodily, especially after the eruption of the second molars [29]. However, it was found that maxillary molar distalization using intraoral appliances can achieve first molar distal tipping of 5.4\({}^{\circ}\), thus providing tooth movement close to bodily movement [30]. Distalization using skeletal anchorage was also reported to result in distalization close to bodily movement. [PERSON] et al. reported maxillary first and second molar distal tipping of 0.31\({}^{\circ}\) and 2.06\({}^{\circ}\), respectively, and mandibular first and second molar distal tipping of 4.95\({}^{\circ}\) and 8.61\({}^{\circ}\), respectively. Likewise, the results of this study revealed maxillary first and second molar distal tipping of 2.66\({}^{\circ}\) and 0.50\({}^{\circ}\), respectively, and mandibular first and second molar distal tipping of 2.30\({}^{\circ}\) and 7.21\({}^{\circ}\), respectively, similar to bodily movement [22]. [PERSON] et al. noted that single tooth distalization is prone to untoward rotation or tipping when the force does not pass through the center of resistance, whereas application of distal force throughout the entire dentition can reduce such adverse effects because the teeth move under a rigid archwire engagement [26]. On the other hand, [PERSON] and [PERSON] pointed out that molar distalization using miniscrew can induce more distal tipping than distalization using dental anchorage, and attributed it to the fact that a distalization appliance using dental anchorage exerts less force posteriorly due to mesial movement of anterior anchorage, whereas the stable anchorage provided by molar distalization using a miniscrew continuously transmits the total force to the posterior teeth [31].