## 5 Discussion  
Functional treatment of growing patients with class II malocclusion can lead to significant skeletal and dentalveolar changes when carried out near the peak of growth. This study shows the results of treatment with F22(r). Young for the correction of class II malocclusion in a group of patients at stage CSV3-CSV4. Before treatment, the 15 patients had an average age of 10.3 years, but were highly compliant, wearing the device for 15/20 h per day for an average total period of 10 months \(\pm\) 0.5 (maximum 11.5 months, minimum 10.5 months). Even if it's possible to start the mandibular advancement with RPE still bonded, T0 records were collected after its removal, in order to analyze just the mandibular advancement benefits with normalized transversal diameters. The resulting improvements in overjet and overbite, and the correction of the molar class on both the right and left sides, are indicators of how effective the device is in resolving class II malocclusion, providing significant normalization of dental parameters. At the level of the upper jaw there were no significant changes; the position of point A remained unchanged, without any alteration in the SNA angle. On this point the literature is controversial. [PERSON] et al. [11] found minimal effects of constriction of upper jaw growth after the use of the Twin Block, which is about 13% of the total skeletal changes. Similarly, [PERSON] et al. [12] showed a small reduction in the SNA angle. The stretching of the surrounding muscles and soft tissues following mandibular advancement could in fact lead to a headgear-type effect, blocking or constricting the upper jaw. However, similar to many studies in the literature, [13] our data do not confirm this outcome, with no significant reduction in the SNA angle. As for the dental effects, i.e., the inclination of the incisors with respect to their bony base, we found that the U1-PP angle was not reduced, while the IMPA increased by about 1.3\({}^{\circ}\) on average. This is an indication that, despite using a lower aligner for anchorage, it was not possible to completely counteract the vestibularisation related to the use of a mandibular advancement device. Considering that the initial position values of the lower incisors were generally increased with respect to the normal range (average at T0: 97.7 \(\pm\) 5.493), the limited gain linked to the functional treatment was not a study group exclusion factor. Since a significant proclination of mandibular incisors is generally found when functional appliances are used during CSV1, CSV2, CSV5, the cervical vertebral stage maturation (CSV3, CSV4) represented an important inclusion criteria [14]. A large difference with respect to other studies in the literature is the non-significant variation in the upper incisor position, which remained largely unchanged. In other studies, the upper incisors were affected by a clinically and statistically significant degree of lingualisation, contributing to the reduction of the overjet [13; 15]. A recent study comparing  
Figure 12: Trend in Co-Gn over time from T0 to T1. the dento-alveolar effects correlated to mandibular advancement performed with Twin-Block Appliance (TB) and Invisalign Mandibular Advancement (MA) confirms that clear aligners better control the incisors inclination. The biomechanical action of clear aligners is very useful in avoiding this great limit of class II functional appliances, since reduction of upper incisors' inclination reduce the potential skeletal mandibular advancement [16]. Another effect that is inevitably linked to this type of treatment is an increase in divergence due to extrusion of the molars, and therefore backwards rotation of the mandibular plane. This was also seen in our patients, but only in part, as the FMA did not change in a statistically significant manner, while the change in MP-SN angle was significant, but probably not clinically appreciable (\(\Delta\) average: +0.86).