## 3 Discussion and Conclusions
The alignment between the intraoral and face scans with a lip-and-cheek retractor shows a mean value of deviation of 0.2848 mm: considering the lower accuracy of the facial scanner compared with the intraoral scanner, this result can be considered clinically acceptable [10] (Figure 12). The alignment between the face scan with a \"voluntary social smile\" and the face scan with the mouth closed with the face scan with a lip-and-cheek retractor is simpler because of the wider surface of the front and nose and the easier identification of cutaneous landmarks. The results of the 3D deviation analysis showed a mean value lower than 0.5 mm, which can be considered clinically acceptable [10; 27] (Figures 13 and 14). Similar to the scanners, orthodontic software packages are also getting simpler and more user-friendly than those from the past years, helping clinicians to obtain a better task in less time. In the future, coding some new orthodontic software packages or integrating the older ones with new specific workflow for face scanning might improve the efficiency and accuracy of this technique. Different methods have been suggested to superimpose three-dimensional surfaces; these can be divided into two categories: landmark- and surface-based methods. Landmark-based methods register 3D images on three or more manually selected corresponding anatomic landmarks. Surface-based registrations use anatomic areas as superimposition references, comparing the triangular representations of the corresponding 3D surface geometries [15]. Surface-based methods are based on \"fine-matching\": this technique reduces the errors associated with manually selecting superimposition landmarks, while the accuracy and reliability improve when 3D models are superimposed [29]. The software Appliance Designer allows matching the 3D images with the command \"Align model-surface-3 points\" combining both the landmark and surface methods together with an increase in accuracy: one first alignment between scans is performed aligning the corresponding three landmarks, then a fine-matching using the \"best-fit\" algorithm between the selected surfaces on the different scans is performed. The virtual dentofacial integration obtained by the present technique permits to create a virtual patient that can be evaluated in three dimensions. This method can help the orthodontist improve the diagnosis and treatment planning: a 3D digital smile design can be performed, the patient's smile can then be analyzed in the context of the lips, and the teeth can be moved in relation to the curvature of the lower lip, intercommissural width, buccal corridors, and gingival architecture to achieve a consonant and balanced smile. All this information can be integrated in a clear aligner therapy or an indirect bonding procedure, enhancing outcomes in facial esthetics [30]. Furthermore, the growing interest in noninvasive diagnosis has allowed the development of new imaging tools without patients' exposure to ionizing radiation: a 3D cephalometric analysis can be performed starting from a facial scan, analyzing the facial morphology and soft tissue profile [31]. Patient monitoring can be also improved, comparing soft tissue changes during orthodontic, orthopedic, or surgical treatment, for a better communication with the patient [32; 33]. The method proposed by the authors might be useful in daily clinical orthodontics, offering future possibilities also to design customized face-driven orthodontic appliances. Further studies should be performed to investigate the accuracy of this technique in comparison with the standard method of aligning facial and intraoral scans with the CBCT data. Conceptualization, G.B. ; writing--original draft preparation, A.C.; writing--review and editing, E.L.M. ; supervision, L.L.M. All authors have read and agreed to the published version of the manuscript. This research did not receive support from funding agencies in the public, commercial, or not-for-profit. Not applicable.