## 4 Discussion
### Manufacturing Process
#### 4.3.2 Selective Bonding Additive Manufacturing  
In an in vitro study, [PERSON] and colleagues [33] compared the accuracy and resolution of two additively manufactured silicones (Sil30 and TrueSil), produced using a selective bonding technique (vat photopolymerization), with two conventional RTV PDMS silicones (A103 and VerSilTal-50F) for potential use in fabricating soft maxillofacial prostheses. The manually fabricated specimens consistently achieved superior resolution compared to the additively manufactured ones, with Sil30 demonstrating the poorest performance. The authors concluded that 3D-printed maxillofacial silicones require further improvement before they can be recommended for clinical use. Additional challenges, such as resiliency, odor, and cost, further limited the feasibility of employing silicones in a direct-to-print workflow [33].  
In an in vitro study, [PERSON] et al. [35] developed a customized binder jetting 3D printing process to fabricate maxillofacial soft prostheses using polyvinyl butyral-coated silicone powder. The aim was to create a novel powder-based 3D printing method that eliminates the need for traditional molds and achieves high-resolution, patient-specific prostheses. Results demonstrated the successful fabrication of geometrically complex silicone parts with satisfactory mechanical properties, including flexibility and tensile strength, comparable to conventional maxillofacial prosthesis. This approach opens avenues for future innovations, including full-color printing, to enhance the realism and functionality of silicone prostheses [35].  
[PERSON] et al. [37] utilized a biocompatible powder and ZBTM58 aqueous binder in conjunction with the Z-Corp Z510 3D color printer to fabricate 30 test cubes. These cubes were used to evaluate the infiltration depth of Sil-25 maxillofacial silicone polymer under atmospheric pressure and at pressures of 2 bar and 3 bar, for durations of 5, 10, 15, 20, and 25 min. Additionally, the study assessed the infiltration depths of two other maxillofacial silicones, Promax-10 and M-3428, under a pressure of 3 bar. The results indicated that increasing pressure significantly enhanced silicone infiltration, with Sil-25 achieving a maximum depth of 8.65 mm at 3 bar. While these findings show promise for prostheses up to 16 mm thick, challenges such as porosity and inconsistent integration between silicone and powder still need to be addressed [37].  
[PERSON] et al. [31] developed an innovative 3D color image reproduction system to automate the additive manufacturing of soft tissue facial prostheses. The system integrated 3D photogrammetry for precise geometry and color capture, binder jetting 3D printing with starch powder, and post-printing silicone infiltration. Conducted by the same research group and using the same 3D printer and Silskin 25 (Sil-25) maxillofacial silicone for infiltration, this study expanded upon earlier work. Results from the in vitro experimentsdemonstrated accurate reproduction of skin color, fine texture, and 3D shape, achieving significant time and cost savings compared to conventional fabrication methods [31].