Effect of bleaching and repolishing on whiteness change and staining susceptibility of resin-based materials

Background The aim of this study was to investigate the effects of different types of bleaching methods and repolishing on the whiteness index and staining susceptibility of additive and subtractive production resin-based materials and direct composite resins. Methods In this study, a total of 96 samples (8*8*2m) were prepared using a nanohybrid composite resin (Neo Spectra (TM)-ST (NS)), a subtractive-manufactured nanoceramic resin (Cerasmart (TM) 270 (CS)), and an additive-manufactured permanent resin (Saremco print Crowntec (CT)). The samples were randomly divided into four treatment groups: control (distilled water, 14 days), in-office bleaching (Opalescence Boost-40% HP, 3*20min), at-home bleaching (Opalescence PF-16% CP, 6 h, 14 days), and toothpaste group (Opalescence Whitening, 2*5min, 14 days) (n:8). After each the bleaching procedure was completed, the samples were kept in coffee solution for 7 days. Following, all samples were repolished. The color of the samples was measured with a spectrophotometer at baseline (T-0), after bleaching (T-1), after staining in coffee (T-2) and after repolishing (T-3). The whiteness index change (triangle W-ID, T-1-T-0), staining susceptibility (triangle E-1, T-2-T-1) and color change after repolishing (triangle E-2, T3-T1) of the samples were calculated in the CIE (Commission International De I'Eclairage) system. The data were analyzed by SPSS software One-Way ANOVA, post-hoc Tukey, post-hoc Tamhane's-T2 and Paired-samples T test (alpha = 0.05). Results The triangle W-ID of all tested materials was significantly different in the in-office bleaching group compared to the control group (p < 0.05). Among the bleaching groups, the highest triangle W-ID was obtained in-office bleaching group of CT (2.91 +/- 4.12). Staining susceptibility after bleaching (triangle E-1) was higher in the in-office and at-home bleaching groups compared to the control group in all tested materials. However, the difference between the treatment groups was statistically significant in NS and CS (p < 0.05). The highest triangle E-1 was obtained in the in-office group of CT (7.36 +/- 4.82). Color changes after repolishing (triangle E-2) of the tested materials were less in all groups compared to triangle E-1. Conclusion In-office and at-home bleaching can increase the whiteness index change and stain susceptibility of materials. Among the tested materials, the color stability of additive-manufactured CT was comparatively poorer. The repolishing was found to be beneficial in reducing staining.