Comparative Evaluation of the Basic Physical Properties of a 3D Printed Experimental Soft Liner versus Conventional Soft Relining Materials

Background: Soft denture liners are essential in prosthodontics for cushioning masticatory forces and enhancing patient comfort. Traditional liners, such as acrylic-based short-term and silicone-based long-term materials, are widely used. With the advent of additive manufacturing, 3D-printed materials have emerged as promising alternatives. However, their physical properties must be thoroughly evaluated before clinical implementation. Methods: This in vitro study compared the color stability, surface roughness, and Shore A hardness of an experimental 3D-printed soft liner with two conventional materials: GC (acrylic-based, short-term) and UP (silicone-based, long-term). Standardized specimens (n = 10 per group) were immersed in distilled water and coffee at 37°C for 1 week, 1 month, and 3 months. Color change (ΔE₀₀) was measured using a spectrophotometer, surface roughness (Ra) with a profilometer, and hardness with a Shore A durometer. Data were analyzed using one-way and repeated measures ANOVA followed by Bonferroni post hoc tests (p < 0.05). Results: The 3D-printed soft liner showed significantly higher Shore A hardness compared to both GC and UP materials across all time intervals. In terms of color stability, the 3D-printed material performed similarly to GC but was inferior to UP. Surface roughness analysis revealed that the 3D-printed liner was rougher than UP, which maintained the smoothest surface and greatest color stability overall throughout the testing period. Conclusions: While the 3D-printed experimental soft liner demonstrated clinically acceptable physical properties, particularly in hardness, its increased surface roughness and moderate color stability suggest that further formulation improvements are needed. Enhancements in softness and smoothness would be necessary for the material to become a viable alternative to conventional soft liners in routine prosthodontic practice.