Abstract
Background: Resin-based composites are most preferred among direct restorative materials due to their highly polished appearance and exceptional polishing abilities. This study aimed to assess the color stability of different types of composite resins after immersion in various solutions and evaluate the effect of home-bleaching on stained composite resins.
Methods: Thirty-six disk-shaped specimens (10 × 2 mm) of each of two composite resins, Spectrum composite and Filtek Z350 XT, were prepared. Specimens of each material (N = 18) were then divided randomly into three groups of six specimens, each according to different types of solutions (Arabic coffee, Cola, Espresso). The rest of ten specimens from each material were stored in 15 ml of artificial saliva to serve as the control. The six specimens in each staining group were further divided into two subgroups. Specimens in each subgroup (n = 3) were treated with one of the bleaching agents. According to the manufacturer’s instructions, bleaching agents were applied to the top surface of the specimens. The color of the samples was measured with a spectrophotometer using CIELAB color space relative to CIE standard illuminant D65 at baseline, after immersion, and after bleaching. The data were analyzed using SPSS version 16.0 (SPSS Inc.Chicago, IL). Color change ΔE* data were analyzed by one-way, two-way analysis of variance , and post hoc Tukey’s test at 0.05 significance level to compare the different groups.
Results: Spectrum composite showed higher color change after staining than Filtek Z350 XT. Arabic coffee induced the most significant color change in the two resin-based composites, followed by Black coffee in Spectrum and Cola in Flitek Z360 XT. After bleaching, both types of composite resin showed a decrease in ΔE values compared to the values obtained after staining. However, there was no statistically significant difference between the bleaching agent groups.
Conclusion: All resin-based materials showed significant color change after immersion in Arabic coffee, Black coffee, and Cola. Spectrum composite showed the highest color change, and Arabic coffee induced the most significant color change. There was no significant difference between Bleaching agent groups. Low concentration (14%-9.5%) of hydrogen peroxide may change the color of the direct tooth-colored restorations, whether recently placed or old, to match that of home bleached teeth.

Key words: Color stability, composite resin, bleaching, discoloration