Evaluation of Bleaching Effect on Tooth Color Change With Different Enamel Thicknesses: An In Vitro Study

Tooth bleaching efficiency may be influenced by enamel thickness, but the particular relationship is not well understood. This in vitro study investigated the impact of enamel thickness on color change following bleaching with 40% hydrogen peroxide (HP) or 15% carbamide peroxide (CP).

Sections were taken from 48 bovine incisors at the cementoenamel junction. Buccal surfaces were cut into 6 × 6 mm² blocks and randomly assigned to four enamel thickness groups: intact, 1, 0.5, and 0 mm (exposed dentin). Each group was separated into HP and CP subgroups. All specimen preparation, thickness adjustments, and bleaching procedures were performed by a single trained operator to ensure consistency and minimize bias. A spectrophotometer (VITA Easyshade V) was used to evaluate color at baseline and after bleaching. ΔE00 and the whitening index (WID) were computed. Statistical analysis was conducted with SPSS v23 (p  < 0.05).

Repeated measures indicated no significant ΔE00 change with extra sessions (p  > 0.05), although WID considerably improved in all groups (p  < 0.05), except for complete enamel (p = 0.127). Enamel thickness had a significant effect on findings (p  < 0.05). Exposed dentin showed higher ΔE00 (p  < 0.05) but lower WID with CP (p  < 0.05), while HP was more effective on dentin (p  < 0.05). The 0.5 mm groups had limited reaction (lowest ΔE00/WID, p  < 0.05). values increased in enamel (p  < 0.05), but dropped in dentin. Most groups showed a significant reduction in values (p  < 0.05). The clinical relevance of WID was supported by the dissociation of ΔE00 (p  < 0.05).

Both agents performed best on intact enamel with a thickness of 1 mm. Enamel with a thickness of 0.5 mm had the lowest ΔE00/WID response. Exposed dentin (0 mm) had the highest ΔE00 but required HP for effective whitening. In this in vitro scenario, WID may be a more relevant efficacy measure than ΔE00. This emphasizes the importance of bleaching methods that are thickness-specific. A single session was sufficient for undamaged enamel; however, several sessions enhanced whitening in thinner enamel and exposed dentin.