Bleaching Systems Effect on Physical Properties of Enamel and Composites

Objectives: To compare the effect of bleaching systems on the color change, surface roughness and surface hardness of enamel and two esthetic composites.
Methods: Bovine enamel specimens (n=16) were embedded, flattened and polished. In each specimen two box shaped cavities (3×3×2mm) were prepared; one filled with Herculite-Ultra composite (HU) and the other with TPH-Spectra composite (TS). The baseline color, roughness and hardness were measured at the two restorations and adjacent enamel, using spectrophotometer (ΔE), optical profilometer (μm) and hardness tester (kgf/mm²), respectively. Specimens were stained with coffee for two weeks, the color was re-measured then they were assigned into 2 bleaching groups: bleaching gel and whitening strips, following stratified randomization. They were submitted to a 10-day cycling test (3-h daily staining and treatments with the assigned bleaching system). After cycling; color, roughness and hardness were re-measured. Differences between baseline and after treatment were considered as outcome measures. Two-way ANOVA model with multiple comparisons using Fisher’s PLSD were used for analysis (alpha=0.05).
Results: Gel significantly improved the color lightness (ΔE 4.9-8.3) and increased the mean surface roughness (Ra 0.04-0.08μm) compared to strips for all substrates (p<0.0001). Enamel color lightness was significantly improved (ΔE 5.4-8.3) compared to HU (ΔE 2.6-4.9) and TS composites (ΔE 2.0-4.9) with either gels or strips (p<0.0001). The mean roughness of TS (0.03-0.08μm), was significantly higher than enamel (0.01-0.05μm) and HU (0.02-0.04μm). Enamel had more decrease in hardness than HU (p=0.0144).
Conclusions: Bleaching gels produced the highest color improvement and surface roughness of all substrates compared to strips. Enamel had significantly better color improvement when treated with gel or strips compared to composite but had the highest decrease in hardness.