Methods: In this prospective single-blind randomized clinical trial, 44 patients with the least mean shade of A3 at their anterior teeth were selected and instructed to use carbamide peroxide (Opalescence 15% gel) into the trays nightly for 14 days. After 3 months, half of subjects received recall bleaching treatments (intervention group) while the other group did not receive recall treatment (control group). Digital images were obtained from the teeth in the baseline, after the bleaching, prior to the recall treatment, immediately after the recall and at 6 and 9-month follow-ups. L*a*b* parameters and overall color changes were calculated on the images by means of Photoshop and CIEL*a*b* system. The data were subjected to analysis of variance for repeated measurements test.
Results: Opalescence 15% gel administration resulted in significant improvement of teeth colors (whiteness) after 9-month follow-ups. The mean overall color changes (Δ E) in the intervention and control groups were 23.84 and 21.57 on 14 days after the initial bleaching, 22.92 and 21.45 before the recall treatment, 27.24 and 23.25 after the recall, 22.61 and 20.45 on the 6-month and 20.46 and 18.2 on the 9-month follow-ups as compared to the baseline values. Therefore, recall bleaching treatments following the initial bleaching was not associated with the increased teeth whiteness until 9 months.
Conclusions: Home bleaching with carbamide peroxide 15% gel showed successful results in teeth whiteness and re-bleaching of the teeth is not recommended up to 9 months after the initial bleaching due to the constant achieved results.