## 2 New Methodologies and Instruments
Reference [28] recently showed how Additive Manufacturing (CAD/AM) techniques are useful not only in surgery planning and in the realization of personalized devices in orthognathic surgery, but also in other fields of medicine like cranioplasty and spine surgery [29; 30; 31]; CAD/AM manufacturing seems to be the future of surgery and a standard procedure is needed for its use in standard operations in order for both surgeons and patients to face the surgery with greater confidence. A problem that should not be underestimated in orthognathic surgery and which is still not fully investigated in the literature concerns the repositioning of the condyles within the glenoid fossa [14]; during orthognathic surgery, the surgeons' skill and experience are mainly relied on the ensure that the positioning is the best possible for the patient (centric relation with the condyles well \"seated\" in the most upward position in the glenoid fossa). Centric occlusion is currently achieved by a traditional or digital custom-made occlusal splint, but centric relation is currently related to the surgeon's sensibility and experience because the mandibular ramus with the condyle cannot be managed by occlusal splints. To prevent unsatisfactory results related to condylar malposition after surgery, researchers recently proposed the use of different skeletal surgical guides to manage ramus and condyle positioning at the fixation time during surgery, each of them showing specific advantages and drawbacks. One of the most used techniques in mandible treatment, as an example, is the Bilateral Sagittal Split Osteotomies (BSSO); the mandible BSSO is the surgical technique that is most widely used for the treatment of mandibular prognathism; this technique was firstly introduced by [PERSON] and then modified by [PERSON], [PERSON], and [PERSON] [32]. BSSO is usually completed with a Z-like distal osteotomy line to prevent any risk for mandibular nerve injury. It involves a full thickness oblique bone cut at the inferior border of the mandible to achieve precise control of the lingual osteotomy and alveolar nerve preservation avoiding osteotome use for splitting maneuvers at the alveolar nerve area [14]. The Obwegeser/[PERSON] osteotomy is a sagittal osteotomy bilateral fractional of the jaw that can extend to the ramus, at the corner and even in the rear part. It divides the jaw into two smaller segments: posterior, carrying the condyle, and a large segment consisting of the mandibular body including the teeth and the chin. Sagittal and extended cutting tends to increase the areas of contact between the segments and therefore to better revascularization and osteogenesis, see Figure 1. However, it can be associated with a high risk of iatrogenic damage to the nervous structures through the splitting procedure. On the basis of this wide scientific literature, in this paper, the authors proposed a new methodology for including the positive experiences of researchers and surgeons and to improve the aspects that bring errors and issues with them. The new idea is to develop a workflow that is able to take into account the problems and to minimize errors with a reduction in operating times and in costs. The workflow is based on massive use of CAD/AM technologies, virtual prototyping, reverse engineering, and new medical devices that allow personalization of the surgery by using standard screws and plates. The proposed method allows us to consider, with high accuracy, the errors' chain and to improve the surgery results thanks to the sequence of operations. Furthermore, the high novelty of the method is also in taking into account the telescopic mechanics of mandibula in case of BSSO, which causes the loss of the centric nature in condylar positioning, and to prevent this common error by a correct virtual surgery planning. The methodology core is based on the development of a special template that is able to drive the surgeon both in cutting and in re-positioning operation and to give them the right guideline for screw implanting.