## 4 Discussion  
As far as the RMEs' effects are concerned, in the literature, statistically significant changes were reported, not only on the transverse plane, but also on the vertical plane. The lowering of the bispinal plane increases the upper (N-Ans) and total anterior facial heights (N-Ans+Ans-Me) and creates a molar rotational hub, resulting in a mandibular post-rotation and in the growth of the anterior facial height [41]. The lowering of the palatal cusps determines the buccal tipping of the teeth with subsequent occlusal pre-contacts that lead to mandibular post-rotation, which temporarily increases the divergence [42]. Some authors reported significant differences on the sagittal plane: [PERSON] et al. [41] showed a forward movement of the jaw, with an increase of SNB and a reduction of ANB that led to a spontaneous improvement of dental II classes in 75% of the sample. In the present pilot study, three patients with skeletal II class due to lower maxilla retraction showed a 2\({}^{\circ}\) decrease of ANB--six patients did not show any changes, and two patients showed a minimal increase. Recently, many studies in the literature observed significant improvements in skeletal II classes after RME therapy [41; 43]. In the present pilot study, the only significant difference among the analyses performed by the two programs concerns the distance between the infraorbital and the mental foramina. According to both programs, the hemi-facial heights on the left and on the right side were increased from T0 and T1 in most of the patients; with Delta-Dent, this difference was found to be significant, whereas with Simplant, it was not. It is difficult to determine which values are more precise; however, it can be confirmed that some slight differences were reported between the two software programs. To the best of our knowledge, only one article in the literature compared two programs [20], and this study also concluded that is not possible to assess whether the discrepancies between the values measured are related to the limited size of the sample or to the different accuracy rate of each program. Furthermore, the sample is not homogeneous as far as the type of device and anchorage of the teeth are concerned. Ten patients were treated with the Hyrax RME, which is characterized by two acrylic pads connected by a stainless steel frame that distributes its forces on the palate, periodontal ligament and buccal bone; this device was cemented onto the second primary molars in six patients, to the first permanent molars in three patients, and to the first permanent molars and premolars in one patient. One patient was treated with a Haas RME, which is a stainless steel rigid structure that exerts its forces on the periodontium [8]. In the literature, some studies discuss how the type of expander may influence the outcomes of RME treatment. [PERSON] et al. evaluated the effects of RME treatment in patients treated with the same two expanders using CBCT, and observed that the Hyrax expander had major orthopedic effects and caused less tipping in the upper first molars [44]. However, [PERSON] et al. three-dimensionally evaluated the outcomes of the Hyrax RME and Haas RME, and reported that the Haas expander induced more orthopedic movement, while the Hyrax expander promoted a major dentoalveolar expansion [45]. Other authors carried out similar comparative studies using 3D software and found no significant differences between the effects of the two expanders [46]. Some studies were carried out to determine whether there were any relevant differences as far as anchorage is concerned. [PERSON] et al. compared the dental arch changes induced by RME treatment related to different types of anchorage and demonstrated how an RME anchored to the second primary molars is associated with an increased expansion in the anterior area and to a more relevant disto-rotation of the first maxillary molars compared to an RME anchored to the first permanent molars [47].