Changes of color, translucency and fluorescence during human enamel bleaching

Methods: Twenty enamel slabs were randomly assigned to acidic 30% HP solution, neutral 30% HP solution, alkaline 30% HP solution and distilled water (DW) (n=5), respectively. Bleaching process was 4×30min, and the time points for measurement were 0, 0.5, 1, 1.5 and 2 h. A colorimeter was employed to measure the L*, a*, b* values of enamel against black, white and yellow backgrounds. Translucency (TP), masking effects (ME), chroma (C*ab) and whiteness index (W*) were then calculated. Laser-induced Raman/fluorescence spectra were recorded by a Raman Spectrometer and the laser-induced fluorescence intensity (FI) was obtained. Data were analyzed by Pearson correlation analysis, multiple linear regression analysis and repeated measure of ANOVA (p < 0.05).

Results: Table 1 showed results of Pearson correlation analysis for baseline values. Multiple linear regression analysis demonstrated that FI of enamel was the most important predictor for ME, C*ab, W* and b*. Table 2 showed results of Pearson correlation analysis for bleached enamel. Repeated measure of ANOVA revealed that all parameters were significantly influenced by time. Compared with DW, HP changed ΔTP, ΔME, ΔC*ab, ΔW*, ΔL*, Δb*, ΔE and ΔFI dramatically (p < 0.001). There was no significant difference among the three bleaching groups on ΔTP, ΔME, ΔC*ab, ΔW*, Δa*, Δb*, ΔE and ΔFI.

Conclusions: 30% HP with different pH values could change the color and translucency of human enamel. Laser-induced fluorescence in the Raman/fluorescence spectra might be used as an indicator to evaluate the kinetics of bleaching within enamel.

Table 1  Results of Pearson correlation analysis for baseline values