## 4 Discussion
The present study showed that the Sander Bite Jumping Appliance is able to modify in a statistically significant way the upper airways at retropalatal and at retroglossal level, according to what has been reported in the literature. The total volume variation (RPV + RGV) was lower than in [PERSON]'s study, which considered the effect of Herbst functional appliance on airway volume and found a volumetric increase of 4187 \(\pm\) 3028 mm\({}^{3}\) on retropalatal air volume (\(p\)-value = 0.052) and a volumetric increase of 5000 \(\pm\) 3676 mm\({}^{3}\) on retroglossal air volume (\(p\)-value = 0.015) between T0 and T1 [43]. Moreover, [PERSON] achieved a more important volumetric variation studying the effect of the MARA functional appliance: the oropharyngeal airway volume (which corresponds to total volume in the present study) increased of 5537 \(\pm\) 4850 mm\({}^{3}\) between T0 and T1 (\(p\)-value = 0.005) [44]. However, the values of volumetric variation obtained in this study were higher than in [PERSON]'s study, which analyzed the effect of a Twin-Block appliance on the upper airways [45]. Regarding the oropharyngeal volume, which corresponds to the total volume (RPV + RGV) of the present study, the volumetric increase was of 1726 \(\pm\) 1205 mm\({}^{3}\) (\(p\)-value = 0.028). The results obtained confirm that an anterior mandible repositioning increases the volume of the airways. Moreover, the oropharyngeal volumetric changes appear to be due to an anterior repositioning of the hyoid bone, which increases the sagittal dimensions of the airways. In fact, after the orthopedic functional treatment, the hyoid bone is brought to an anterior position together with the jaw by the suprahyoid muscles. The orophyneal volumetric increase allows a reduction in the mechanical impedance to the air flow; however, treatment with a Sander Bite Jumping Appliance alone cannot be sufficient for treating OSAS, as it is a multifactorial pathology [46]. [PERSON] et al. published in 2020 a systematic literature review with meta-analysis on the effect on the upper airways of functional orthopedic treatment of class II malocclusions. He observed a statistically significant increase in nasopharyngeal volume, especially through the use of removable functional appliances, which appear to lead to a greater increase in airways than do fixed functional appliances [47]. [PERSON] and [PERSON] in 2021 published a scoping review of 18 studies and found that 72% of these reported an increase in oropharyngeal and hypopharyngeal airways using fixed functional appliances due to mandibular advancement [48]. [PERSON] et al. in 2022 published a literature review in which, on the contrary, it is concluded that there is too little evidence, due to too small samples and the absence of randomization, control group and long-term outcomes to support that functional equipment can be effective in treating OSAS in children [49]. A limitation of this study is represented by the fact that this is a pilot study and no sample size calculation was performed. Additionally, no control group was considered in the study protocol; this was owing to the fact that it is considered unethical from a radiological and therapeutic point of view to perform two CBCTs in less than a year and an orthodontic treatment on young patients who do not need them. However, this does not allow one to detect whether the increase in oropharyngeal spaces could be due even to the physiological growth of the patients, in addition to the usage of the appliance. For instance, [PERSON] et al. [50], as in the present study, evaluated the short-term effects of the Sander Bite Jumping Appliance on the pharyngeal airways in skeletal Class II malocclusion patients. By means of cephalometric evaluations, the authors found that the orophyneal region increased in the treated group, but the difference was not statistically different with respect to the control group.