Effect of fabrication technique on surface roughness and color stability of novel resin occlusal veneers after thermomechanical aging: an in-vitro study

Abstract Background Resin-based occlusal veneers are increasingly used within minimally invasive restorative dentistry. However, evidence remains limited regarding whether fabrication technique (subtractive milling versus additive 3D printing) influences clinically relevant surface characteristics particularly surface roughness and color stability after thermomechanical aging. Methods Eighteen resin occlusal veneers were fabricated from the same standardized digital design (STL) using NanoKsa G-Plus material and divided into two groups ( n = 9): milled CAD/CAM and 3D-printed. Measurement of surface roughness (Ra) was performed utilizing a non-contact profilometer at baseline and after thermomechanical aging while Color change (ΔE) was assessed with a spectrophotometer (Vita Easyshade) sequentially: after coffee immersion (1 week) and then repeated again after thermomechanical aging. Thermomechanical aging combined thermocycling (5000 cycles) and chewing simulation (75,000 cycles) under standardized loading. Intergroup comparisons were performed using independent t-tests, with level of significance determined at p ≤ 0.05 and 1.0 < ΔE*ab threshold range < 3.3 commonly reported clinically acceptable thresholds. Results At baseline, the 3D-printed group showed significantly greater roughness of surface than the milled group (Ra: 0.27 ± 0.007 vs. 0.24 ± 0.02; p = 0.05). After thermomechanical aging, no significant difference was detected between groups (Ra: 0.26 ± 0.021 vs. 0.27 ± 0.016; p = 0.50). For color change, the 3D-printed group demonstrated significantly greater ΔE than the milled group across all intervals, including baseline-to-post-staining (34.33 ± 6.14 vs. 13.14 ± 2.31; ` p = 0.001) and post-staining-to-post-aging (18.78 ± 3.85 vs. 2.66 ± 1.89; ` p < 0.001`). Conclusions Thermomechanical aging reduced differences in surface roughness between milled and 3D-printed resin occlusal veneers; however, 3D-printed specimens exhibited substantially higher discoloration after staining and aging. This may indicate that, despite comparable post-aging roughness, color stability may limit the clinical use of 3D-printed in situations where esthetics are critical indicating that their recorded stainability values exceeded commonly reported clinical acceptable thresholds.