## 4 Discussion
### Visualization of the Defect and Design Software  
For converting the DICOM data obtained from medical scanning (e.g., CBCT) and generating a surface mesh (Stereolithography file format - STL), an image editing program is used, with a threshold tool allowing a range of values to be set from the data to be retained while ignoring data that falls outside the range [13; 83]. This is a very useful tool for retaining or removing areas of interest, corresponding to the density values of tissue types [84], and due to recent advances in segmentation software, it can be done automatically or semi-automatically [85]. Commercially available software was preferred, with Mimics (Materialise,Belgium) being used in most of the published reports [22; 31; 42; 43; 46; 54; 60]. The open-source software 3D Slicer (The Slicer Community) and Slic3r were each used in one case. [PERSON] et al. [1] compared a digital workflow using open-source software with the same workflow performed with commercially available software for designing five prosthetic templates of maxillofacial defects. The open-source software consisted of Slicer 4.10.2 for CT, MITK workbench (GCRC, Germany) for CBCT and Meshmixer 2.1 (Autodesk Inc., USA) for CAD. The commercially available software used was the software package developed by Materialise (MIMICS and 3-matics). The authors managed to design the templates for all the defects using both types of software. For less complex defects, such as auricular replacement, both the open-source and commercially available software were theoretically capable of producing accurately reproducible prostheses for patients. For more complex defects, the commercially available software had significantly improved abilities [1]. This fact could explain the extensive use of commercially available software (Table 1). At least two different categories of software were used in the digital workflow of maxillofacial prosthesis fabrication: software for reverse engineering the patients' data into a digital format (data editing) and CAD software. To date, one of the major drawbacks is the requirement of skilled dental technicians familiar with CAD or a digital design engineer for assisting through the entire process. The software and interface used to assist the design of the maxillofacial prostheses were often intended for medical or general purposes, which made the designing process more complicated and required more originality. Despite being used in a great number of dental laboratories, the dental design software does not provide specific features for maxillofacial surgery or prosthodontics. [PERSON] et al. (2019) [86] described a case with the use of 3 Shape software (Coppenhagen, Danemark) and adapted its features for designing a surgical template for implant insertion for facial prosthesis retention. The great advantage of most of the frequently used CAD dental software is that the different types of files (e.g., DICOM, STL, OBJ) could be superimposed [87; 88], providing useful and detailed information of the area to be rehabilitated and eliminating the use of multiple pieces of visualization software. For anatomic part design, a CAD-assisted mirroring and merging technique is frequently used for auricular prostheses, orbital prostheses or if the defect is limited to the midline. For other types of defects, such as those of the nose or the maxillary obturator, creating an accessible library is extremely useful. The lack of a library makes the design challenging and requires the creation of anatomic parts from scratch [1]. A few research groups created such databases (or libraries). [PERSON] et al. 2013 [57] created the Ear&Nose Digital Library of real anatomic models by scanning plaster casts from conventional impressions taken during the annual hands-on educational course of Maxillofacial Prosthodontics at the Dental School of the University of Bologna. [PERSON] et al.