Effect of Intracoronal Barrier Location on Bleaching Efficacy and Peroxide Diffusion

Objectives: The influence of intracoronal barrier positioning on bleaching effectiveness in different tooth regions and on hydrogen peroxide diffusion remains unclear. This study analyzed how the positioning of the cervical barrier affects chromatic changes in different dental regions and the diffusion of hydrogen peroxide in bovine teeth undergoing internal bleaching. Methods and Materials: Eighty bovine incisors were sectioned at the root, at a position 5 mm apical to the cementoenamel junction (CEJ). A 2-mm-thick cervical bleaching barrier was fabricated using resin-modified glass ionomer cement. The teeth were divided into two groups (n = 40) based on the positioning of the cervical barrier: coronal or apical to the CEJ. In the first phase, 40 teeth (n = 20 of each cervical barrier group) were stained with equine blood. Internal bleaching was performed with 60 μL of 35% H2O2 over three sessions at seven-day intervals. Chromatic change and whiteness index were assessed in root, cervical, and incisal regions using a portable spectrophotometer (three-way ANOVA, Tukey post hoc test). In the second phase, the remaining 40 teeth underwent a 45-minute whitening session and were analyzed for H2O2 diffusion using an enzymatic reaction method between the leucocrystal enzyme and peroxidase. (one-way ANOVA, Tukey post hoc test). Results: The barrier placed apical to the CEJ showed significantly greater chromatic differences and whitening index than the coronally placed barrier in the root (ΔE00 = 19.79, p = 0.02; ΔWID = 19.69, p < 0.001) and cervical (ΔE00 = 10.05, p = 0.03; ΔWID = 16.08, p = 0.02) regions at 21 days; no significant differences were observed in the incisal region (ΔE00 = 8.17, p = 0.07; ΔWID = 19.09, p = 0.08). Hydrogen peroxide diffusion was significantly higher for the apical barrier than the coronal barrier (2.2 μL vs 1.2 μL, p = 0.001). Conclusion: Chromatic differences in the root and cervical regions depended on cervical barrier position. A barrier apical to the CEJ provided greater bleaching effectiveness in these regions. However, hydrogen peroxide diffusion was also increased when the barrier was positioned apically.