Effect of High Bleaching Concentration on Enamel and Subsequent Staining

While bleaching is extremely popular aesthetically, little has been reported about detrimental effects with excessive use, especially with increased bleach concentrations. OBJECTIVES:This study tested the hypothesis that repeated applications of a 35% bleaching concentration would affect the enamel and increase the staining susceptibility of the tooth. METHOD: A 35% carbamide peroxide (CP) solution was made. Extracted teeth were sectioned, dentin area coated with clear acrylic, placed in individual vials and immersed in Fusayama Artificial Saliva (FAS). The experimental halves were immersed in 35%CP solution for 1hr at 37°C. Teeth were stained in standardized tea solution for 4.5hrs. Between treatments, specimens were incubated at 37°C for 1wk in FAS (changed daily). The procedures were repeated 3 times. A Minolta CR-300 colorimeter was used for CIEL*a*b* measurements. Measurements (9 per sample) were recorded at 10 intervals for three treatments: pre-bleaching, post-bleaching and post-staining. Stained specimens were measured, brushed to remove any residue, and re-measured. SEM; EDS; semi-quantitative analysis and statistical analysis using the L*a*b* colour parameters were performed. RESULTS: Paired t-tests showed statistical significance between BL3 and ST3; BL1 and ST1; BL2 and ST2. SEM micrographs depicted distinct changes in the enamel surfaces. SEM, EDS and semi-quantitative analysis of enamel surfaces revealed [25.5%-34.9%Ca(K)] and [13.9%-16.7%P(K)]. When DE had statistical significance (p=0.0001), the graphs of DL and Db were inversely related. The graphs were not related when there was no statistical significance (BL2 and BL3). In comparisons with no statistical significance, Da exhibited higher values. CONCLUSIONS: After one bleaching treatment there was a moderate increase in value (L*) and no significant increase in staining. However, these study results showed a statistically significant increase in staining after the second and third bleaching treatments (p=0.0001).