Effects of Different Bleaching Agents on the Surface Topography and the Microhardness of Artificial Carious Lesions

Objectives: The aim of this study was to evaluate the effects of in-office and at-home bleaching agent applications on the surface topography and microhardness of artificially demineralized enamel.

Materials and methods: A total of 224 enamel specimens were prepared using bovine sound central incisors. 4 mm × 4 mm enamel windows were exposed on the buccal surfaces covering the remaining surface with nail varnish. Samples were immersed in a demineralizing solution for 16 hours to produce artificial caries lesions, then divided into four groups according to the bleaching agent's type and concentration. Group I; in-office bleaching 35% hydrogen peroxide (HP) (Whiteness HP Maxx; FGM, Brazil), Group II and Group III at-home bleaching 16 and 22% carbamide peroxide CP, respectively (Whiteness Perfect). Group IV; control (not bleached). The microhardness Vickers hardness number (VHN) was measured at the baseline, after demineralization, and after bleaching consequently. The micro-surface changes of the enamel surface after demineralization and bleaching were evaluated by scanning electron microscope (SEM).

Statistical analysis: Data were evaluated by the one-way analysis of variance (ANOVA) test followed by Post Hoc Tukey's and Fisher's least significant difference. Tow- sided p-values were considered statistically significant at p ≤ 0.05.

Results: A significant reduction was noticed in the enamel microhardness after demineralization p < 0.05. However, there is no statistically significant difference between the mean VHN of the demineralized and bleached enamel (p > 0.001). SEM images showed significant changes on the surface of the demineralized enamel after bleaching (pattern type III).

Conclusions: The low and high concentrations of HP and CP bleaching agents increased the demineralization severity of artificial caries lesions without significantly altering their microhardness values.