Adhesive-based protective strategies for enamel cracks during in-office bleaching and their effect on hydrogen peroxide penetration

Abstract

Abstract Objectives To evaluate hydrogen peroxide (HP) penetration in teeth with enamel cracks and to investigate if adhesive-based strategies can reduce its permeability without compromising bleaching efficacy (BE). Materials and methods Fifty human premolars ( n = 10 per group) were allocated into five groups: unbleached sound teeth (control), bleached sound teeth, bleached teeth with enamel cracks without adhesive strategy (cracked enamel), and two groups with enamel cracks receiving adhesive protection prior to bleaching (three-step etch-and-rinse adhesive [3-stepER] and universal adhesive used in an etch-and-rinse strategy [UA-ER]). Enamel cracks were detected using transillumination and measured using ImageJ software. In the adhesive groups, phosphoric acid etching was followed by adhesive application before two bleaching sessions. HP penetration into the pulp chamber was quantified using UV–Vis spectrophotometry. Color was assessed at baseline and after 7 and 14 days using digital spectrophotometry. Final bleaching efficacy was calculated from the color change between baseline and day 14 (ΔE ab, ΔE 00 and ΔWI D ). Data were analyzed using one-way ANOVA followed by Tukey’s post hoc test (α = 0.05). Results HP penetration differed among the bleached groups ( p < 0.05). The sound group showed the lowest HP levels (0.21 ± 0.06 µg mL⁻¹), whereas the cracked enamel (0.36 ± 0.23 µg mL⁻¹) and 3-stepER (0.32 ± 0.11 µg mL⁻¹) groups showed similar intermediate values. The UA-ER strategy showed the highest HP penetration (1.81 ± 0.34 µg mL⁻¹; p < 0.05). No significant differences in BE were observed among the bleached groups. Conclusions Neither adhesive-based strategy provided a protective effect against HP diffusion in teeth with enamel cracks. The 3-stepER strategy did not reduce HP penetration compared with unprotected cracked enamel, whereas the UA-ER strategy resulted in significantly greater HP penetration, indicating an adhesive-dependent response. Clinical Relevance The use of adhesive systems as a protective strategy during in-office bleaching may not effectively reduce HP diffusion in teeth with enamel cracks. Clinicians should exercise caution when adopting such approaches.