Can thermal cycling and iron supplement exposure alter the esthetic performance of bioactive dental materials?

The aim of this study was to evaluate the color stability of contemporary bioactive restorative materials, including Equia Forte HT, GC Fuji II LC, ACTIVA BioACTIVE, Cention N, and a conventional composite resin, and to comparatively analyze their color changes following thermal aging and exposure to iron preparations. A total of 120 specimens were fabricated from five different restorative materials: Equia Forte, Cention N, ACTIVA BioACTIVE, Fuji II, and SolareX (n = 24 per group). All samples were initially subjected to thermal cycling, followed by immersion in two iron-containing solutions (Ferrum and Ocean) and one control solution (distilled water) for 72 h. Measurements were recorded at baseline (after 24 h of immersion in distilled water), after thermal cycling, and following staining procedures. Color difference (ΔE00) and lightness (L*) values were quantitatively assessed using a dental spectrophotometer based on the CIEDE2000 color evaluation system. Statistical analyses were performed using the Shapiro-Wilk test, Kruskal-Wallis test, and generalized linear models (GLM) approach. All analyses were conducted with SPSS version 22.0, with a significance level set at p < 0.05. A statistically significant difference was observed between the baseline and post-aging color values (p < 0.05). Among the materials tested, Equia Forte exhibited the greatest degree of color change, while ACTIVA BioACTIVE and SolareX demonstrated similar and comparatively lower levels of discoloration. Although no statistically significant difference was found between ACTIVA BioACTIVE and SolareX regarding total color change from baseline to final measurements (p > 0.05), the ΔE2 values of Equia Forte, Cention N, and Fuji II were significantly higher than those of the SolareX group (p < 0.05). Furthermore, significant differences were noted in the L* values before and after aging depending on the restorative material used (p < 0.05). Equia Forte showed the lowest L* values at both baseline (L1) and post-aging (L2), whereas ACTIVA BioACTIVE and SolareX presented the highest values. The findings of this in vitro study suggest that the color stability of restorative materials is influenced by intrinsic material properties as well as exposure to thermal aging and staining solutions. These factors should be considered when selecting restorative materials, particularly in esthetically demanding clinical situations.