Effect of tooth-bleaching methods on gloss and color of resin composites

The purpose of the study was to evaluate gloss and color changes of resin composites after exposure to different bleaching agents.

Products used, were: Nite White ACP (10% carbamide peroxide gel), Crest Classic and Supreme Whitestrip (6.5% and 14% hydrogen peroxide strips, accordingly). A hybrid (Herculite XRV) and a nanohybrid (Premise) resin composite were exposed to the bleaching agents. Twenty-four disk-shaped specimens per composite were subjected to bleaching by each of the agents (n=8) for up to 2 weeks. Color changes using CIE-L*a*b* system (50:50% acceptability threshold: ΔE*=3.3) were recorded after 1 and 2 weeks bleaching cycles relative to baseline measurements. In addition, gloss measurements (in gloss units) were performed at the same bleaching intervals and gloss changes were calculated.

All bleaching agents tested provided decrease in gloss of both composites after 2-week bleaching (p<0.05). No differences were detected among the three bleaching regimens, for up to 2-week application, in terms of color and gloss changes on both composites. After the 2-week bleaching period, hybrid composite presented higher gloss reduction (%) than nanohybrid regardless of the bleaching agent (p<0.05). Color change (ΔE*) was lower than 3.3 for all composite-bleaching agent combinations. After 1- and 2-week bleaching time, the nanohybrid composite provided higher color change than the hybrid under all bleaching procedures (p<0.05). No strong correlation was proved between color (ΔE*) and gloss changes caused by bleaching treatments.

After 2-week bleaching cycles, composites showed significant gloss reduction (p<0.05). Color alteration was below the 50:50% acceptability threshold (ΔE*<3.3) and it was product-depended. There was no significant difference in color and gloss changes between the evaluated bleaching strips and 10% carbamide peroxide gel.