Furthermore, this finding could support a hypothesis that has been accepted by a previous study stating ��light could www.selleckchem.com/products/CP-690550.html produce an initial effect that is not sustained for a long time.[20] Regarding efficacy and longevity, there is a positive correlation between the rebounding of mineral density of the tooth and the degree of lightening. Using the at-home bleaching technique, the teeth receive a continual application of hydrogen peroxide during which the demineralization and remineralization processes interact.[4] While in power bleaching, the color regression is primarily a result of the reversal of whitening which is due to just the remineralization process.[21] Furthermore, power bleaching can have a dehydration effect on bleached teeth, which interferes with the evaluation of the color differences.
In the present study, in order to decrease the consequences of whitening such as dehydration of teeth, the color evaluation of bleached teeth was done 2 h after the completion of the bleaching procedure rather than immediately thereafter. Even though, this time is insufficient for complete rehydration of the bleached teeth there is a limitation on delaying the color evaluation any longer because the regression of whitening might occur and interfere with the true results in terms of the degree of whitening and color regression. This procedure also has already been described by Li et al.[4] Bizhang, et al.,[22] Marson, et al.[23] concluded that the at-home bleaching and in-office bleaching techniques were equally effective at the 3 months interval time after bleaching.
The result of these studies could support the findings at the 3 months post-treatment time interval of the present study. However, the post-treatment evaluation period of these two studies were very short, which made it difficult to detect any loss of whitening. Bernardon, et al.[24] found no difference in the bleaching result with regard to sensitivity and durability at the 6 month post-treatment interval. They used at-home bleaching with 10% carbamide peroxide versus in-office bleaching using 35% hydrogen peroxide activated with a LED/diode laser for two sessions each week for 2 weeks. The result of Brandon’s study is in contrast with the present findings regarding rebound effect. This difference could be probably due to either the mode of light activation or the frequency of power bleaching that was performed in that study.
As for color difference between rebounded tooth color and unbleached teeth; (��E3), the values (5.6848 �� 2.34) and (6.9507 �� 3.18) resulted from power bleaching and Drug_discovery at-home bleaching respectively, with no significant difference between them. This means that the whitened teeth showed an identical color relapse after 6 months. While, evaluating within groups showed no significant difference between ��E1 and ��E3 in this respect.