الفهرس 
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Abstract
This in vitro study was evaluated to compare the effect of two hydrogen peroxide based bleaching agents one of them contained remineralizing agent (Flouride) and the other is Flouride free on the microhardness of enamel surface just after the bleaching and after remineralization for 7 and 14 days of daily application using MI paste.
A total number of 49 anterior permanent bovine teeth were extracted from sacrificed bovine jaws, scaled to remove soft and hard tissue debris and the roots of all the teeth as well as the incisor halves of crowns were cut off. The enamel labial surface of teeth was flat ground. Samples were divided into two main groups of 21 samples each according to the bleaching agent (Oplalescence Xtra Boost and Power Whitening). Each main group was then divided into 3 subgroups according to the time of remineralization with MI paste (7 days and 14 days). In addition, there was control group (n=7/group). Vickers microhardness test was performed and statistically analyzed .
The results showed that the control group, Power Whitening and Opalescence bleached samples after remineralization with MI paste for 14 days had the higher statistical significant microhardness than other groups without statistical significant difference between them. The Power Whitening bleached samples after remineralization after 7 days showed lower statistical significant microhardness than previous groups but had higher statistical significant microhardness than Opalescence bleached samples after 7 days of daily application of MI paste. In contrast, the samples treated with Power Whitening and Opalescence without reminerlization as well as treated with Opalescence after 7 days of remineralization showed the least statistical significant microhardness without statistical significant difference between them.