## 4 Discussion
### Properties of 3D-Printed Materials for Maxillofacial Prosthesis  
Ideally, materials for soft maxillofacial prostheses should possess a balanced combination of physical, mechanical, and biological properties to ensure optimal functionality, durability, and patient comfort. The desired characteristics include the following [8; 44; 45; 46]:  
Mechanical and physical properties:  
High tensile strength, tear strength, edge strength, and abrasion resistance to withstand mechanical stresses. Recommended, ideal values are provided in Table 3;  
Dimensional stability to maintain shape and fit over time;  
Low thermal conductivity and glass transition temperature for patient comfort;  
Resistance to solubility and water absorption to prevent deformation and microbial growth;  
Surface integrity and low surface tension to enhance longevity and maintain aesthetics;  
Ensuring strong adhesion for the anchorage of the retention system [47];  
Lightweight to ensure patient comfort and to facilitate prosthesis retention. Color and aesthetic properties:  
Long-term color stability, even under different environmental and weather conditions;  
Transparency to allow intrinsic pigmentation and customization with cosmetic colorants;  
Resistance to pigment fading, with white pigments and nano-oxides enhancing stability. Biological and functional properties:  
Tissue compatibility, including non-toxicity, non-inflammatory, and non-allergenicity;  
Odorless and inert to adhesives and solvents for ease of use; \begin{table}
\begin{tabular}{c c} \hline \hline
**Mechanical Properties** & **Ideal Values** \\ \hline Tear strength & 30 to 100 psi (53 to 175 N/m\({}^{2}\)) [39; 48; 49; 50] \\ Tensile Strength & 300 to 1000 psi (2.0 to 7 MPa) [49; 50] \\ Elongation at break & 400 to 800\% [39; 48] \\ Modulus at 100\% elongation & 345 to 1720 kPa [39; 48] \\ Hardness & about 40 preferably in the range 25–35 Shore A [39; 49; 50] \\ Glass transition temperature & less than 0 [39; 48] \\ Heat distortion temperature & above 120 [39; 48] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Ideal physical and mechanical properties of materials used in maxillofacial prosthesis manufacturing according to the published literature. Permeability to moisture release while resisting microbial adhesion;
* Maintenance of softness during use for comfort. According to a recent literature review by [PERSON] et al. [44], which analyzed 88 articles, primarily in vitro laboratory studies, the authors concluded that no material is currently considered ideal. However, silicone remains the most commonly used due to its superior balance of properties compared to acrylic-based materials. Innovations such as incorporating nano-oxides and tulle reinforcement, combined with optimized processing and maintenance techniques, can significantly enhance the performance and longevity of soft maxillofacial prostheses. Heat-cured silicones are preferred for their superior color stability compared to room-temperature-cured alternatives. Intrinsic pigmentation using pre-colored molds and advanced processing methods further improves durability. Additionally, proper maintenance, including the use of mild disinfectants and protection from harsh environments, can extend the prosthesis's lifespan. These findings apply to materials used in both conventional and partially digital workflows. Regarding the fully digital workflow, based on the eleven articles included in this review, the information on the properties of materials suitable for manufacturing soft maxillofacial prostheses is limited. Although these studies explore various approaches to direct 3D printing, they provide only preliminary insights into material performance, clinical outcomes, and long-term feasibility. Specifically, data on the daily wearing of prostheses and their medium- to long-term durability remains scarce. Of the five clinical cases reviewed, none included medium- or long-term follow-up. [PERSON] et al. [10] reported a follow-up duration of six months, while [PERSON] et al.