## 2 Materials and Methods  
Our research was conducted based on an analysis of different surgical areas (Table 1, Figure 1):  
* Reconstructive surgery  
* Fractures of the orbital floor
* Fractures of the zygomatic arch
* The COVID-19 pandemic \begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{3}{c}{**Our experience in CAD/CAM applications in Maxillofacial Surgery**} \\ \hline \multicolumn{3}{c}{**Ordinary activities**} \\ \hline \multicolumn{3}{c}{**Application field**} & **Specific application** & **Cases** \\ \hline \multicolumn{3}{c}{Reconstructive surgery} & Cutting-guide & 4 \\ \hline \multirow{3}{*}{Traumatology} & Orbital mesh conformer & 9 \\ \cline{2-3}  & Zygomatic shield & 16 \\ \hline \multicolumn{3}{c}{**Extraordinary activities**} \\ \hline \multicolumn{3}{c}{**Application field**} & **Specific application** & **Cases** \\ \hline \multicolumn{3}{c}{Covid-19 pandemic} & Ffp2-n95 face mask & 6 \\ \cline{2-3}  & Covid-19 face shield & 6 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Our cases ordered according to pathology. The first step was based on the study of radiographic investigations. The computer tomography (CT) scans necessary in our protocol were generated by means of high-resolution computer tomography. The CT scanner used was a Canon (ex Toshiba) 16 slice, which acquired the data with a 0.5 mm nominal slice width, reconstructed to a 1024 \(\times\) 1024 matrix. A segmentation process based on threshold, region growing, and watershed techniques was performed on the Digital Imaging and Communications in Medicine (DICOM) files of the CT scans. This method allowed us to obtain a 3D reconstruction of the surface of interest. Our investigation involved the use of the Invesalius software, a program which involves intuitive and rapid segmentation, selecting the appropriate window (skin rather than bone) [4]. CT DICOM files were used. Once the 3D model had been obtained, it was exported as a Standard Triangulation Language (STL) file. In the editing phase, the Meshmixer software proved to be extremely useful, as well as easy to apply [5]. Through specific tools such as \"Extrude\" and \"Export\", it was possible to mold and edit the shape of the device, obtaining a customized tool for each patient. This was exported and made printable in 3D using the CURA software [6] (Figure 2). Figure 1: Graphical representation of our cases. Figure 2: Digital workflow of our study showing in detail every application necessary for the 3D print process (every application is completely open source). A. Reconstructive surgery in oncological cases  
Between January and September 2016, four patients undergoing mandibular reconstruction with a free osteocutaneous fibula flap were enrolled in our protocol. All the patients were affected by squamous cell carcinoma of the mandibular alveolar ridge. They had been briefed on the procedure and had given their consent for the processing and registration of data in our unit of clinical research. Traditionally, this surgery is based on free-hand segmental osteotomies. The free-flap harvesting represents a challenge for the surgeon, involving a steep learning curve, with the results varying according to the surgeon's experience. The main stages of the preoperative and surgical workflow were as follows (Figure 3). Transformation of the DICOM data into STL files. Design of virtual osteotomies and surgical guides. The surgical guides were molded directly on the mandibular surface in correspondence with the defined osteotomy lines under control CT recurring to the margin of oncological radicality. Production of surgical guides. Virtual cutting guides for both the jaw and fibula were exported as STL files. These STL files were imported into the CURA software and optimized for an ULTIMAKER 2 3D printer. The material used was 2.85 mm Bioflex medical PLA flexible filament (polylactic acid) (ISO 10993-5: 2009). Surgery. This involved a modified radical lymphadenectomy in all cases ipsilateral to the lesion.