## 2 New Methodologies and Instruments  
The use of Computer Aided Design and Manufacturing (CAD/CAM) techniques brings great results and progress both in orthognathic surgery and in aesthetic surgery. Ref. [6] underlined the advantages in the use of CAD/CAM techniques not only in surgery planning, but also in design and manufacturing of cutting guides, occlusal splints, and custom-made plates for assisting the surgeons in correct repositioning of bone segments. Ref. [7] showed how the CAD/CAM approach improves the surgeons' capabilities through the virtual preoperative planning that allowed the reduction of operating time and surgical impact on patients. The accuracy of the innovative methodologies for maxillary repositioning has been evaluated in a timely manner, comparing the new methods with the Conventional Model Surgery (CMS) [8; 9] in scientific literature; research suggests that the most important limitation of traditional techniques lies in the transfer of quantitative information between plaster casts and the articulator and patient's face skeleton. A limitation of traditional techniques for craniofacial modeling is that they tend to focus on dental occlusions without taking into account the movement of the jaws [10]. As reported in ref. [11], the comparison between the traditional approach and the one that uses innovative technologies showed the relevance of the use of the third dimension for diagnostic purposes, for the planning of the treatment, and for the definition of the surgical operation in the History of orthognathic surgery. In ref. [8], for example, it was demonstrated how in VSP techniques the higher error (about 2 mm) in the maxillary position is better than the best outcome given by CMS, and the jaw repositioning and functionalities takes advantage of that. An important factor that can determine the success or failure of an intervention lies in the perfect control of the movements; this aspect can be managed through today's \"computer aided\" technologies [9]; through 3D planning techniques, the surgeon can more easily understand, thanks to the virtual prototyping of the intervention, which procedures should be addressed to correct deformities and to achieve perfect symmetry and harmony of the face. Furthermore, intraoperative manipulations are drastically reduced thanks to the preventive design of surgical guides that allow cutting and positioning of bones considering the personal patient's bone morphology. There has been a growing interest in the last 20 years for Computer Aided Surgery (CAS) techniques; this entailed a search for low-radiation diagnostic systems, better-performing commercial software, and rapid manufacturing techniques [12]. Even if CAS more easily entails errors because of the uneasiness complexity of use of Virtual Surgical Planning (VSP) instruments like Computer-Aided Design (CAD) programs and 3D visualization programs [8], the VSP is a powerful tool because it allows us to create and show, in a virtual environment, all the conditions that both the surgeon and the patient could face on and provides instruments to reach the surgery goal [13; 14]. The surgery planning enhanced by the computer-aided techniques, nowadays, includes different types of approaches such as advanced imaging, analysis, software, and the creation of prototypes using additive manufacturing techniques [12]. The combination of VSP, CAD, Computer-Aided Manufacturing (CAM), and 3D visualization allows surgeons to plan, virtually, manipulations and the translation of the human parts in the operating room [15]. Computer-Aided (CA) techniques can be used for different types of surgery; in craniosulfacial surgery, there are two main approaches: image guided and template guided. The first one uses images to drive the surgeons in their operations, while the second one, instead, uses physical templates and special devices to perform the surgery [12]. In both cases, CA techniques start with the collection of the data to plan the needed manipulations for positioning the bones [4].