## 4 Discussion
[18] demonstrated that central and lateral incisors' crown exposures were statically greater after expansion completion, underling their extrusion and an increase in OVB. This is in accordance with [PERSON]'s theory of equilibrium [50], which might explain the spontaneous retraction and alignment of the upper incisors. The CAs group showed significant increases in maxillary incisor inclination and OVJ values, while there was a reduction in OVB. Furthermore, if RME only acted on the first permanent molars, clear aligners were digitally set on the alignment of the arches and the proclination of the upper incisors, leaving an OVJ value at least 2 mm to allow for mandibular growth. Advantageously, this technology enables movements on the three space dimensions simultaneously, correcting different issues at the same time [37] by levelling the dental arch and determining a partial midline correction through a digital plan. After treatment in the RS group, the primary canine stayed in the same position or underwent a slight lingual torque. As explained above, the creation of space in the anterior area after expansion likely provided the canines with more space and allowed them to lingualize, following the same movement of incisors. [PERSON] et al. [49] have confirmed that 5.3 and 6.3 showed no statistically significant increase in angulation, proving that no dental tipping or dentoalveolar compensation were observed. The appliances used in the present study were not anchored to canines, which might have caused a smaller increase in the intercanine arch width [50]. Conversely, in the CAs group, the maxillary canine angulation was increased because the primary canines showed greater buccal tipping at the end of the treatment. According to the previous literature, one protocol recommended an overcorrection during dentoalveolar expansion and inclination of the anterior teeth for functional and aesthetic reasons [24]. Our results are in agreement with recent studies which reported that clear aligners are able to determine dentoalveolar expansion in the intercanine width, changing the arch-form in the anterior and lateral regions especially [51; 52; 53; 54; 55]. Evaluating the changes in gingival display after therapy, there were statistical differences between the two groups. The RS group evidenced an increase in the skeletal size of the anterior region of the maxilla, which allowed the incisors to move without any clinical control. Similar observations have been described in the literature, as Van Der Linden F.P.G.M evidenced the extrusion and lingual inclination of anterior teeth after RME [56]. Conversely, the CAs group evidenced better management of this clinical aspect, showing improved leveling of the upper arch with proper movements (anterior intrusion and posterior extrusion) and controlling the inclination of the anterior teeth at the same time, as demonstrated by a reduction in gingival display in the incisor and canine regions with the CAs. Therefore, this therapy encouraged correction of the excessive OVB values and guarantees adequate incisor inclination for future mandibular growth in children. These results confirm those reported by [PERSON] et al. [57], who reported that a sequential expansion protocol with CAs which included a correction of anterior crowding induced significant modifications in gingival contour, resulting in a more harmonious smile. For these reasons, accurate management of the gingival display and smile aesthetics is possible even in early treatments utilizing this appliance [58]. The outcomes of our research highlight that both therapies guarantee adequate arch expansion in young subjects with moderate maxillary contraction. Clear aligners are a treatment option also suitable for performing phase 1 of orthodontic treatment. Phase 1 treatment in the presence of narrow maxillary arches is traditionally performed via RME and represents early interceptive orthodontics treatment for growing patients with mixed dentition.