## 4 Discussion  
The scientific literature reveals that VSP is a valid and reliable method to assist surgeons in different procedures, ranging from reconstructive surgery with free flaps [5; 6; 7; 8] to orthognathic surgery procedures [9; 10; 11], facial traumatology [12], correction of craniosynostosis [13], osteogenic distraction [14; 15], and even facial allograft transplantation [16]. In Table 2 we report the most relevant articles that have influenced and guided our research (Table 2). The initial goal of the VSP was to produce a stereolithographic model that could assist the surgeon in reconstructing craniofacial defects or in performing orthognathic surgery [17]. In orthognathic surgery, the possibility of developing a 3D model obtained by integrating VSP represents a significant advantage thanks to the possibility of an accurate representation of facial asymmetries [18; 19]. In addition, VSP provides an accurate assessment of the temporomandibular joint relations [20], which can be corrected in the event of discrepancies in the orthognathic surgery. CAD/CAM models make excellent planning possible in maxillary surgery, allowing the surgeon to guide the osteotomy and the repositioning of the jaw [21]. [PERSON] et al. used customized titanium plates and CAD/CAM cutting guides for maxillary repositioning without using splints [22]. [PERSON] and [PERSON] reported significant improvements in accuracy in virtually designed cases [23]. Through a comparison of the bone reference points in the post-operative phase, they detected average deviations of 4.11 mm in the simulation group and 6.92 mm in the conventional group. With the conventional method, [PERSON] et al. reported, in their case history, a deviation of 6 mm. This, however, was reduced to 1.5 mm in the group with virtual design [24]. Mandibular reconstruction with free flaps represents another challenge addressed by means of this technology. The protocol we apply involves in-house prototyping in order to model the mesh based on the patient's anatomy. The time involved for the design allows a clear reduction in operating times. The accuracy of the printing depends on the accuracy of the CT, which must have slices thinner than 1-2 mm [25]. Next, the intrinsic capabilities of the printer and its components must be considered: for precision printing, a nozzle of at least 0.4 mm must be used and the accuracy of the printing profile must be close to 0.1-0.06 (fine/ultra-fine), thereby avoiding the requirement to print supports to reduce the alterations of the printing surface. Moreover, again in the area of maxillofacial trauma, we have applied this rapid in-house prototyping method to patients suffering from zygomatic fractures [26; 27]. Several authors have described the use of protective masks to be applied in this area to allow adequate bone consolidation [28; 29]. We therefore produced virtually, through specific software, our customized restraint device for each patient, so that it could adhere completely to the skin surface of the individual subject. The cost of the prototyping process is around 5 euro for each case, and the time required for the CAD programming is around 90 min [25]. VSP offers significant advantages in terms of the duration and predictability of the operation thanks to pre-formed cutting guides [30]. The benefits of CAD/CAM reconstructive procedures include the pre-surgical planning of the tumor resection and the final flap positioning. VSP proved to be more accurate and efficient than traditional surgery [31]. With this technique, similar outcomes have been obtained from surgeons with different levels of experience [32]. Indeed, the pre-surgical planning of the cutting lines and flap size allows a considerable reduction in the duration of any ischemia, related to the time previously used for the shaping of the flap [24]. \begin{table}
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The main disadvantages are the cost and delivery time of the product.