According to the findings of the longevity of vital bleaching, we found that the longevity of both types is a maximum of 6 months; while in contrast to the results of the present study, Swift et al.[25] showed that satisfactory results persist for 1-2 years and patient should be advised regarding the need for re-bleaching procedures Wortmannin mTOR for 1 week every year. In that study, color evaluation was using only a Vita 3D Master shade guide that was not quantitative. Post-treatment sensitivity of teeth, results from the penetration of peroxide through the enamel and dentin tubules to the pulp. Cooper et al.[26] claimed that this takes approximately five 15-min to occur. This explains why the color of dentin adjacent to the pulp can be whitened as rapidly as the dentin along the dentinoenamel junction.

[27] There was no significant difference between both methods regarding tooth sensitivity. This finding leads to the acceptance of the third null hypothesis of the study. One previous study demonstrated that sensitivity persisted for up to 4 days after treatment.[28] However, a longer duration of sensitivity up to 39 days has been reported as well.[29,30] In the present study, the overall percentages of subjects who experienced mild tooth sensitivity after bleaching were 42.9% for the at-home bleaching and 57.1% for power bleaching. This finding is same as the results of previous study carried out by Tavares et al.[31] who found no significant difference between at-home and power bleaching procedures. Kossatz et al.[32] found a range of 50 to 80% of patients experienced post-treatment tooth sensitivity after power bleaching.

Matis et al.[33] showed that the subjects who received three 15-min treatments with light activation expressed less gingival and tooth sensitivity than that was observed with one application of H2O2 within 40 min. In the present study, 38% H2O2 was applied in three 15-min treatments as a preventive strategy. One of the limitations of this study was to not to test the re-bleaching procedure as well as the efficacy of doing so. A second limitation is related to the interval time between the 3 and 6 month evaluation intervals. This was very long in comparison with the other time intervals of this study and probably led to the inability to determine the exact time of color regression.

Drug_discovery As a result, it is not known if color regression occurred between the 3rd and 4th month interval or the 4th and 5th month interval or the 5th and 6th month post-treatment time interval. However, it is statistically clear that in-office bleached teeth reverted back to the original color sooner than at-home bleached teeth. The specific time when this occurred in this study could not be determined beyond that it was between the 3rd and 6th month time interval. However, it is important to note that after 6 months there was no trace of the whitening effect produced by either the at-home or in-office bleaching methods.