## 4 Discussion
However, the current study clearly showed a relationship between the duration of application of antioxidant materials and the reduction in dissolved oxygen; specifically, we showed that applying antioxidant materials for 48 h can minimize or even almost eliminate peroxide residues on teeth after bleaching. The mean differences in and distributions of dissolved oxygen between intervention groups at 1 h, 24 h, and 48 h were tested with a one-way ANOVA test (\(p<0.05\)) thatshowed that there were significant differences in the mean dissolved oxygen among sodium ascorbate 10% combined with Tween 80 0.2%, _Trigona_ spp. propolisis 10%, and the control (without antioxidants). However, running [PERSON]'s HSD test (\(p<0.05\): significant difference) between the groups, i.e., _Trigona_ spp. propolisis 10%, sodium ascorbate 10% combined with Tween 80 0.2%, and the control, at observation times of 1 h, 24 h, and 48 h showed no significant difference between dissolved oxygen in the _Trigona_ spp. propolisis 10% and 10% sodium ascorbate combined with Tween 80 0.2% groups. This result is not in line with the opinion of [PERSON] et al. (2010) that the antioxidant properties of propolis allow it to absorb free radicals and protect against gamma radiation better than vitamin C (ascorbic acid) [53]. However, studies conducted by [PERSON] et al. (2014) compared propolisis from China and Egypt with ascorbic acid and showed that ascorbic acid was more effective than propolisis at low concentrations whereas, at high concentrations, propolisis showed better antioxidant activity than ascorbic acid [54]. Propolis, rich in flavonoids, phenolics, and tannins, has good antioxidant properties through its ability to donate hydrogen from its hydroxyl group and its ability to donate electrons to resist the production of free radicals as a result of oxidative stress [55; 56]. Meanwhile, the antioxidant effect of ascorbate is derived from its ability to react directly with a broad spectrum of reactive oxygen species, stop the chain reactions initiated by free radicals through electron transfer, and participate in the regeneration of the antioxidant properties of fat-soluble vitamin E [56]. Propolis has 1,1-diphenyl-2-picrylhydraz1 (DPPH) radical-scavenging activity that is higher than that of ascorbic acid due to propolisis containing ascorbic acid in addition to flavonoids and phenolics that act as antioxidants [25; 56]. A study reported the absence of a significant difference in the microctensile bond strength in teeth that had been bleached with 35% carbamide peroxide and were exposed to propolisis or 10% sodium ascorbate as antioxidants [52]. However, the results of this study showed that the mean microctensile bond strength of propolisis was higher than that of ascorbic acid [52]. Based on the current study, the results suggested that using propolisis for 48 h successfully diminished peroxide remnants after an intra-coronal bleaching treatment which, in turn, made it possible to improve composite bonding and reduce waiting periods for composite restorations after the bleaching treatment. A limitation of this study is that a restoration strength test was not carried out after the applications of bleaching agents and antioxidants. Finally, further studies are needed for clinical applications, with larger sample sizes and varied follow-up periods to strengthen the evidence for the depletion of residual peroxides produced after intra-coronal bleaching through the application of antioxidant agents obtained from _Trigona_ spp. propolisis.