Impact of Smear Layer Removal Protocols on Color Dynamics and Dentin Hardness Following Intracoronal Bleaching

Kwunklao Saichuea; Boonrat Sattapan; Boonlert Kukiattrakoon; Kewalin Thammasitboon

doi:10.31584/jhsmr.20251218

Authors

Kwunklao Saichuea Dental Department, Roi-Et Hospital, Roi-Et 45000, Thailand.
Boonrat Sattapan Department of Conservative Dentistry, Faculty of Dentistry, Prince of Songkla University, Hat Yai, Songkhla 90112, Thailand.
Boonlert Kukiattrakoon Department of Conservative Dentistry, Faculty of Dentistry, Prince of Songkla University, Hat Yai, Songkhla 90112, Thailand.
Kewalin Thammasitboon Department of Conservative Dentistry, Faculty of Dentistry, Prince of Songkla University, Hat Yai, Songkhla 90112, Thailand./ Research Center of Excellence for Oral Health, Faculty of Dentistry, Prince of Songkla University, Hat Yai, Songkhla 90112, Thailand.

DOI:

https://doi.org/10.31584/jhsmr.20251218

Keywords:

CIEDE2000, CIELAB, dentin hardness, Intracoronal bleaching, smear layer, Sodium perborate

Abstract

Objective: This study evaluated the impact of smear layer removal protocols on intracoronal bleaching outcomes, focusing on color shifts and dentin hardness.
Material and Methods: Artificially stained human premolars underwent dentin surface treatments: distilled water, 17% EDTA, and 37% phosphoric acid (PA) before intracoronal bleaching with sodium perborate. Control teeth received no treatment. Tooth color and dentin hardness were measured at 7, 14, and 21 days post-bleaching with a VITA Easyshade spectrophotometer and Vickers hardness tests, respectively. Statistical analysis included Shapiro-Wilk and Levene’s tests, and two-way repeated ANOVA with Tukey’s HSD for shade and microhardness comparison (α=0.05).
Results: All the bleaching treatments effectively lightened teeth, with the most pronounced color change (ΔE00) observed after the first week. This was followed by a significant decrease in intensity during the second and third weeks. Color metrics showed reduced redness (a* values) and increased yellowness (b* values) across all the groups, with no significant differences in color change or dentin hardness between the treatments (p-value>0.05). However, a notable decrease in dentin hardness was observed in the cervical sections compared to the coronal sections in all the groups (p-value<0.05).
Conclusion: Smear layer removal with 37% PA or 17% EDTA did not significantly improve bleaching efficacy or affect dentin hardness. These findings support streamlined treatment protocols that omit smear layer removal without compromising clinical outcomes.

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