Do bleaching gels affect the stability of the masking and caries-arresting effects of caries infiltration-in vitro

Objectives The aim of this study was to evaluate the influence of different bleaching gels on the masking and caries-arresting effects of infiltrated and non-infiltrated stained artificial enamel caries lesions. Materials and methods Bovine enamel specimens (n = 240) with each two sound areas (SI and SC) and each two lesions (DI and DC) were infiltrated (DI and SI), stained (1:1 red wine-coffee mixture,70 days), and randomly distributed in six groups to be bleached with the following materials: 6%HP (HP-6), 16%CP (CP-16), 35%HP (HP-35), 40%HP (HP-40), and no bleaching (NBl,NBl-NBr). Subsequently, specimens were pH-cycled (28 days, 6 x 60 min demineralization/day) and all groups except NBl-NBr were brushed with toothpaste slurry (1.100 ppm, 2x/day, 10 s). Differences in colorimetric values (Delta L, Delta E) and integrated mineral loss (Delta Delta Z) between baseline, infiltration, staining, bleaching, and pH cycling were calculated using photographic and transversal microradiographic images. Results At baseline, significant visible color differences between DI and SC were observed (Delta E-baseline = 12.2; p < 0.001; ANCOVA). After infiltration, these differences decreased significantly (Delta E-infiltration = 3.8; p < 0.001). Staining decreased and bleaching increased Delta L values significantly (p <= 0.001). No significant difference in Delta Delta E was observed between before staining and after bleaching (Delta E-bleaching = 4.3; p = 0.308) and between the bleaching agents (p = 1.000; ANCOVA). pH-cycling did not affect colorimetric values (Delta EpH-cycling = 4.0; p = 1.000). For DI, no significant change in Delta Z during in vitro period was observed (p >= 0.063; paired t test). Conclusions Under the conditions chosen, the tested materials could satisfactorily bleach infiltrated and non-infiltrated stained enamel. Furthermore, bleaching did not affect the caries-arresting effect of the infiltration.