Effect of post-polymerization exposure times and material thickness on color stability of 3D-printed definitive restoration resins: An in vitro study.

PURPOSE: This study aimed to investigate the effect of post-polymerization exposure time and material thickness on the color stability of three-dimensional (3D)-printed definitive restoration resins with varying filler compositions. MATERIALS AND METHODS: Three A1-shaded definitive restoration resins, VarseoSmile Crown Plus (R1), saremco print CROWNTEC (R2), and P-Crown V3 Ceramic (R3), were evaluated. Disk-shaped specimens (8 × 2 mm, 8 × 4 mm) were 3D-printed under controlled conditions. Subsequently, each material thickness group was divided into four subgroups (n = 15) representing post-polymerization exposure times of 0, 2000, 4000, and 6000 flashes using a post-curing device (Otoflash; NK Optik GmbH). Color coordinates were measured using a spectrophotometer, and color differences (ΔE00) were calculated using the CIEDE2000 formula. The Vita 3D Master 1M2 shade was used as the control reference. Data were analyzed using three-way analysis of variance and Tukey's test (α = 0.05). RESULTS: All tested resins exhibited color changes exceeding the clinical acceptability threshold (ΔE00 > 2.25), with color deviations recorded for R1 (ΔE00 = 3.43-6.79), R2 (ΔE00 = 3.54-6.45), and R3 (ΔE00 = 7.30-12.14). Among the post-polymerized specimens, R2 at 4 mm thickness with 6000 flashes post-polymerization achieved the best color fidelity (ΔE00 = 3.54 ± 0.31). Notably, the manufacturer-recommended 4000-flash protocol produced the greatest overall color deviation. Resin type (partial η2 = 0.940), post-polymerization exposure time (partial η2 = 0.733), and material thickness (partial η2 = 0.089) significantly affected color stability (p ≤ 0.001). Overall color fidelity ranked as R2 (mean ΔE00 = 5.07), followed by R1 (mean ΔE00 = 5.60), and R3 (mean ΔE00 = 9.55). CONCLUSIONS: Manufacturer shade designations alone are insufficient for predicting the final color of 3D-printed resins. Post-fabrication shade verification is essential, as the final color deviates significantly depending on the material and post-polymerization protocol. The optical properties of additively manufactured definitive restorations may deviate from standard shade references to a clinically unacceptable level depending on material thickness and post-polymerization protocols. Relying exclusively on manufacturers' nominal shade codes or recommended curing protocols could result in esthetic mismatches.