Effect of Post-Curing Time on the Color Stability of 3D-Printed Hybrid Resin Material, an In Vitro Study

Objectives: This study investigated the effect of post-curing time on the color stability of a non-polished, as-printed hybrid 3D printed resin material and assessed whether a nitrogen atmosphere during post-curing has any influence. Methods: The 3D-printed specimens were divided into four groups based on the post-curing time (5, 10, 20 and 30 min) and two subgroups with and without nitrogen. Color changes ( E) of the specimens, immersed in coffee for 30 days, were measured using a spectrophotometer at different ageing times: first at baseline and 7,15 and 30 days after immersion. Data were analyzed with Shapiro–Wilk, Kruskal–Wallis, Fisher exact and Mann Whitney tests. Results: Statistically significant differences were found in E values across all post-curing times (5, 10, 20, and 30 minutes) at each time point of measurement (T1, T2 and T3), with or without nitrogen. Shorter curing durations (especially 5 minutes) resulted in higher E values, indicating more noticeable color changes. Conversely, longer curing times, particularly 30 minutes, exhibited the best color stability, with E values often below the clinically acceptable threshold of 3.3, especially when nitrogen was used. However, the bivariate analysis did not always show statistically significant differences between groups with and without nitrogen, except at select time points. Conclusions: The study found that longer post-curing times improved the color stability of 3D-printed hybrid resin, with 10 minutes being generally sufficient. Most samples exceeded the acceptable color change threshold after extended coffee immersion, though longer curing delayed this effect. The use of a nitrogen atmosphere during curing had no significant impact.