## 3 Results
In this study, 28 patients who were already undergoing orthodontic treatment with Invisalign were randomly allocated into two groups. Patients in the first group received tooth bleaching using 10% carbamide peroxide for 8 h a day for 4 weeks while patients in the second group did not receive dental bleaching. Tooth shade, gingival index (GI), and plaque index (PI) were evaluated at baseline, and at two-week intervals for 6 weeks using the VITA classical shade guide, the Turesky Modification of the Quigley-Hein Index, and the Loe and Silness gingival index, respectively. The authors reported a significant change in tooth shade in the study group over the two- and four-week periods, as well as a reduction in gingival and plaque indices. This is shown by the reduction in tooth shade from 6.1 at baseline to 2.6 at 2 weeks and 1.6 at 4 weeks. Overall, 44% of the patients in the study group showed an improvement of 3-6 shades, 28% showed an improvement of 1-2 shades, while another 28% showed an improvement of more than 7 shades, with an average shade improvement of 3.5 shades after 2 weeks. In contrast, the patients in the control group maintained a consistent shade average of 6.43 to 6.46 during the study. The authors reported dental sensitivity in one subject in the experimental group, which was attributed to a pre-existing gingival recession and was resolved by reducing the exposure time to carbamide peroxide for less than 8 h, despite the fact that all patients were asked to use a toothpaste containing potassium nitrate to reduce the risk of dentine hypersensitivity. Moreover, the authors reported that the use of carbamide peroxide, which decomposed into urea and hydrogen peroxide, resulted in an increased plaque and saliva pH which in turn reduced caries and gingival inflammation. This is shown by the significant decrease in the PI from 1.8 at T0 to 1.2 at T2 and to 1.11 at T4, as well as the significant decrease in the GI in the experimental group from 0.53 at T0 to 0.08 and 0.05 at T4 and T6, respectively. In addition, the presence of the highly reactive hydroxyl radicals, which reacted with the bacterial membrane lipids and DNA, resulted in bacterial cell death. Furthermore, evaluation of the teeth at the sixth week revealed that the teeth maintained the shade improvement and gingival health 2 weeks after bleaching termination. Limitations of the study included the small sample size and the fact that the examiners were not blinded to the intervention. [PERSON] et al. (2019) evaluated the efficacy of different home bleaching methods during orthodontic treatment with F22 aligners [37]. Thirty-eight patients were allocated into four different groups; patients in group 1 received home bleaching using 3% hydrogen peroxide for nine hours per day over days 7-14 of aligner use, patients in group 2 received home bleaching using 10% carbamide peroxide for nine hours per day over days 7-14 of aligner use, patients in group 3 received home bleaching using 16% carbamide peroxide for nine hours per day over days 7-14 of aligner use, while patients in group 4 received home bleaching using 16% carbamide peroxide for nine hours per day over days 1-14 of aligner use. The shade of the six maxillary anterior teeth was evaluated before treatment (baseline, T1) using a VITA Easyshade V compact in three areas per tooth (incisal, middle, and cervical), in which every value on the scale was given a numerical equivalent. A Kruskal-Wallis H test was used to compare the median shades for each site on the six upper teeth before whitening and showed that there were no statistically significant differences among the patients in the four different groups, meaning that the patients in the four groups belonged to the same population. This protocol was repeated after two weeks (T2) for colour analysis after application of the bleaching agents for nine hours by the patients. The authors reported the shade improvements for groups 1, 2, 3, and 4 as 51.0%, 57.0%, 60.4%, and 73.0%, respectively, when comparing the mean shade values at T1 to those at T2.