## 4 Discussion  
Nowadays, it is necessary for the surgeon to plan the facial aesthetics of his patients very carefully, because it is usually the first patient's concern. Almost all patients who are to undergo orthognathic surgery present some degree of facial asymmetry [9]. Even in cases of second- or third-class correction, it is uncommon that an asymmetric component is not also detected. The surgical correction of facial asymmetry is particularly complex because several parameters contribute to defining the symmetry of the face. A correct chin position and lateral projection of the mandibular angles contribute to generating a good final result [11]. When planning the correction of the chin in space, it is necessary to ask the orthodontist for the correction of the lower dental midline in relation to the bony chin. When this orthodontic result is obtained and the case is planned on an articulator mounting, the dental midline is well representative of the bony chin since the two structures are very close to each other. This is not the case for the mandibular angle region; in fact, the lower molars are too far from the mandibular angles to represent their movement in space. There are anatomical and clinical situations that may affect the distance between these two regions. The distance may be large when the whole mandible is large in class III patients, or when premolar extraction in the lower arch moves molar in a mesial direction. On the contrary, the distance is short in class II patients when the whole mandible is deficient and/or no extractions are planned in the lower arch. The larger the distance between the molar and the angle of the mandible, the greater the difference between the apparent movement of the angle on model surgery and the angle real movement. Although the planning of orthognathic surgery is now mainly done with dedicated software, which allows the digital simulation of the osteotomy lines and movements of the maxilla-mandibular complex, it is equally true that not all healthcare structures are equipped with these technologies. These structures continue to use model surgery, which in any case has a long history behind it [20]. Centres that treat a limited number of dento-maximilofacial deformity cases often do not use 3D reconstruction software because of the high cost of these technologies and the long learning curve associated with them [21]. The authors believe that the present study may contribute to the implementation of new 3D technologies in these structures as well. The advantages that these software packages bring to everyday clinical practice are certainly several. They allow great precision in surgery planning and make it possible to carry out various plans on the same patient very quickly [22]. They are also useful from a teaching point of view, as they as they have a great communicative impact on students and doctors in specialist training once they have learnt how to use them [22]. The Authors' research is therefore directed at both of these schools of work: in the case of using plaster models in the articulator, one must consider errors and risks in the analogue-only approach, as explained in the previous sections of this article; in the case of using three-dimensional software, on the other hand, this article further validates the accuracy of this digital workflow. For all these advantages, model surgery will certainly only be used in the future in limited cases, while only 3D technology will be used for routine surgery. The present work adds further technical detail in support of this modern 3D technology. Conceptualization, C.D.B. and A.D.B. ; methodology, B.V. and M.D.B. ; software, C.D.B. ; validation, F.D.F., A.L. and G.M. ; formal analysis, M.S. ; investigation, M.D.B. and B.V.; resources, M.D.B. ; data curation, F.D.F., A.L. and G.M. ; C.D.B. and A.D.B. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Informed Consent Statement:Informed consent was obtained from all subjects involved in the study.