Influence of Specimen Pre-staining on In Vitro Whitening Efficacy of Hydrogen Peroxide Gels

Various in vitro approaches have been used to evaluate whitening efficacy, utilizing both stained and non-stained tooth substrates, which may influence the outcomes. This study aimed to assess the effect of previous in vitro staining on whitening efficacy and the enamel surface using hydrogen peroxide (HP) gels with different concentrations.

Bovine enamel/dentin specimens (n=16) were randomly allocated into groups according to the HP concentration [20% (HP20), 30% (HP30), 40% (HP40), and deionized water (negative control)]; and substrate condition (non-stained or stained). Tooth color was measured using a spectrophotometer, and the color difference (ΔE00) and whiteness index (WID and ΔWID) were calculated. Knoop surface microhardness (SMH) and roughness (Ra) of enamel were assessed at different times. Data from both non-stained and stained substrates were analyzed using ANOVA and Tukey post hoc tests (α<0.05).

Significant differences were observed in ΔE00 for different HP concentrations and substrate conditions (p<0.001). Greater tooth color change was found for HP 40, followed by HP30 and HP20. Stained groups exhibited higher ΔE00 values than non-stained ones, except for HP20. Higher values of ΔWID were observed in stained/bleached groups. The staining process reduced SMH and increased Ra.

The bleaching patterns were similar for both non-stained and stained substrates, with higher concentrations of HP bleaching gels resulting in greater tooth color difference. Previous staining increased the variation in whiteness values (ΔWID) following bleaching, but specimens maintained a lower whiteness index after bleaching compared to the non-stained substrate. Staining induced alterations on the enamel surface. These factors indicate that pre-staining of specimens is not essential to evaluate the whitening efficacy of bleaching gels.