## 4 Discussion
[23], reported significant changes in the upper airway dimensions in a sample of skeletal class II patients with SDB, using a different type of orthodontic device, whereby the patients were treated with a functional appliance aimed at mandibular advancement. In addition, their median follow-up period was 20 months. That device also included a maxillary expansion screw, which was activated once a month; therefore, another important difference with our study was that they obtained a dentoalveolar expansion, rather than a skeletal expansion. Post treatment, [PERSON] et al. observed a reduction in SDB, a reduction in the size of adenoids, an increase in pharyngeal width, and a forward relocation of the tongue and the hyoid bone in relation to the mandibular base. Lastly, they also recorded an improvement in skeletal class II cephalometric parameters, specifically, the ANB angle. Thus, it can be said these studies confirm that the expansion of the upper arch, even if dentoalveolar, increases the width of the airways. Regarding the skeletal class (ANB angle) cephalometric improvement, while pre-treatment study subjects revealed an ANB angle of on average 4.95\({}^{\circ}\) (\(\pm\)2.1\({}^{\circ}\)), i.e., skeletal class II, the post-treatment average value was reduced to 3.3\({}^{\circ}\) (\(\pm\)1.1\({}^{\circ}\)), i.e., to class I, with a statistically significant reduction (\(z=-2.75\); \(p=0.00\)). In our study, before treatment, 13 out of 20 patients had a skeletal class II relationship (ANB \(>\) 4\({}^{\circ}\)), while, after treatment, nine of them showed a class I ANB value. Thus, four subjects remained in class II even after treatment. In the literature, the correction of skeletal class requests a treatment based on a mandibular advancement [24]. Correction of the skeletal class was associated with a greater advancement of the mandible compared to the maxilla, although, in both dental arches, there was a statistically significant increase at T1. In reviewing the literature, it can be observed that, in patients with skeletal class II treated with rapid maxillary expansion, correction of class II does not always occur. For example, [PERSON] et al. observed no class II correction in their sample of 30 children treated with both types of rapid palatal expander (banded or bonded), but respiratory function was neither considered nor included in their study [25]. Similarly, in a study by [PERSON] et al. [19], following orthodontic treatment in conjunction with rapid maxillary expansion, no significant changes were found in the cephalometric values concerning the skeletal class II; after a 12 month treatment, the cephalometric analysis did not show significant changes in the SNA, SNB, and ANB angles, whether in patients with resolution of sleep breathing disorders following the orthodontic therapy carried out or in those who still exhibited SDB post orthodontic treatment, although the latter group of patients, with residual sleep-disordered breathing, showed larger ANB values in comparison with those who showed a resolution of the aforementioned condition, without a statistically significant difference between the two groups. It should be noted that the age of the patients in [PERSON]'s study ranged from 4 to 10 years, including patients in deciduous dentition. Thus, from data by [PERSON] et al. and from the present sample, it can be concluded, on the basis of [PERSON]'s data and corroborated by our data, that pediatric patients with skeletal class II and affected by SDB can experience a skeletal class normalization after a maxillary rapid expansion. In the present investigation, the study subjects did not show many other cephalometric variations, except for the sagittal position of the maxilla and the mandible in relation to the anterior skull base (the variables SNA, SNB, and ANB angles) (Table 4).