Evaluation of color stability and mechanical properties of 3d-printed complete denture base materials

Additive manufacturing technology has gained significant ground in digital dentistry due to its appealing clinical and laboratory advantages. However, for 3Dprinted complete dentures to fully replace conventional alternatives, they must possess superior mechanical, aesthetic, and physical properties. The primary aim of this study was to comparatively evaluate the flexural strength, microhardness, color stability, surface roughness, water sorption, and solubility of four different 3Dprinted complete denture base materials against a conventional heat-polymerized denture base material. This study investigated five different denture base materials: one conventional heat-polymerized material (Probase-HC) and four distinct 3Dprinted denture base materials (NextDent-ND, Formlabs-FL, Senertek-ST, Powerresin-PR). Test specimens were prepared in two primary forms: bar and disc shaped. Bar-shaped specimens (64×10×3.3±0.2 mm) were used for flexural strength, microhardness, surface roughness, and color stability tests. A total of 180 specimens were fabricated, with 20 from the Probase-HC group and 40 from each of the four 3D-printed groups. Conventionally fabricated bar specimens underwent mechanical polishing only. In contrast, 3D-printed bar specimens were randomly divided into two subgroups for either mechanical polishing or glazing. Subsequently, these specimens were subjected to 5000 cycles of coffee thermal cycling (CTC). Color change (ΔE00) and surface roughness (Ra) were assessed both before and after CTC. Following these assessments, a three-point bending test and Vickers microhardness (VH) test were performed. Disc-shaped specimens (50±1×0.5±0.1 mm) were used for water sorption and solubility tests. A total of 100 specimens were produced, with 20 from the ProbaseHC group and 20 from each of the four 3D-printed groups. No surface treatment was applied to these disc-shaped specimens. In this present study, a total of 280 specimens were utilized for a comprehensive evaluation of material properties. Statistical analysis of the data was performed using descriptive and analytical methods, with a significance level set at α=0.05. The results of this study generally indicate that the 3D-printed denture base materials exhibited acceptable values for flexural strength, microhardness, surface roughness, color stability, water sorption, and solubility when compared to the heatpolymerized conventional denture base material. The application of Vita Akzent® LC (VA) glaze material, while providing supplementary protection against surface degradation during coffee thermal cycling (CTC), resulted in a statistically significant increase in initial surface roughness (Ra) values across all experimental 3D-printed groups (p<0.05). Glaze application reduced the ΔE00 value of the FL group (p=0.036) but did not exert a statistically significant impact on the ΔE00 of the other 3D-printed groups (p>0.05). Additionally, VA glaze enhanced the VH of most 3D-printed groups (p<0.05). It improved the flexural strength of the PR and ST groups but decreased it for the FL group and had no significant effect on the ND group (p=0.088). Mechanically polished specimens demonstrated acceptable Ra, ΔE00, and flexural strength values. However, their VH values were found to be lower than those of the glazed specimens. In conclusion, while glaze application led to improved mechanical strength and hardness in the majority of 3D-printed groups, its capacity to effectively reduce surface roughness and discoloration was consistently limited. Conversely, mechanical polishing maintained its beneficial effects, demonstrating clinically acceptable values across all assessed parameters. Therefore, comprehensive additional investigations are necessary to fully elucidate the performance characteristics of glaze materials and their interactions with 3D-printed denture base materials.