Post-curing strategies for enhanced polymerization and color stability in 3D-printed composite crowns

Additive manufacturing technologies in dentistry have enabled the fabrication of definitive restorations using 3D-printed resin composites. However, the effects of different post-curing protocols on the surface hardness and optical stability of these materials remain underexplored.

To evaluate the influence of various post-curing protocols on surface hardness and optical properties-including color change and translucency-of a 3D-printed resin composite for permanent crowns.

Disc-shaped specimens (10 mm × 1 mm, n = 10 per group) were fabricated using a 3D-printable resin composite. Post-curing protocols included exposure to 405 nm light (Wash & Cure Plus for 30 or 60 min; ProCure 1 ONX-mode) and to 385 nm light (ProCure 2 in "Surgery Guide" and "Bego" modes). The control group consisted of non-post-cured samples. After 24 h, surface Vickers hardness (200 g load for 15 s) and color change and translucency (L∗, a∗, b∗, and translucency parameter - TP₀₀) were measured using a benchtop spectrophotometer. After 7 days, all samples received an additional 40 s of light exposure simulating cementation, and color changes (ΔE00) were reassessed. Data were analyzed using one-way ANOVA and Tukey's post hoc test (α = 0.05).

Hardness values significantly increased with curing time and wavelength (p < 0.001), with ProCure 2 yielding the highest values. Translucency remained stable, regardless of the tested group. The highest color change was observed in the non-cured group (ΔE00 = 3.21 ± 0.27) and decreased significantly with the post-curing procedures, especially with the 385 nm-based source (ΔE00 = 1.02 ± 0.18).

Post-curing significantly enhances the surface hardness and long-term color stability of 3D-printed resin composites compared to uncured samples. While a 385 nm light source provides the greatest hardness, it may induce initial yellowing that could be clinically unacceptable.