الفهرس 
Introduction .Only 14 pages are availabe for public view
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Abstract
The aim of this study was to evaluate the DC of adhesive resin and the bonding effectiveness of dental composite resin restoration to bleached enamel after using 2 different types of antioxidants with 2 different preheating temperatures at 2 different application durations and compare them with unbleached and bleached groups using etch and rinse adhesive system.
One of the main concerns about bonding to bleached enamel is the lower bond strength obtained due to the inhibition of resin polymerization by the residual oxygen left behind after the bleaching process which mandates delayed bonding until complete elimination of oxygen is achieved.
In attempt to reduce the waiting time the use of antioxidants after bleaching was advocated due to their free oxygen scavenging ability. DPPH assay was used to assess the antioxidants activity of both AO preheated or not.
FTIR spectroscopy was used in measuring DC of adhesive resin and bond strength was evaluated using μSBS test, stereo microscope and Fractographic analysis of debonded samples was performed using Scanning electron microscope examination.
The specimens were divided according to the type of antioxidant used into 6 different groups (No bleaching, Bleaching only, B+PBE-R, B+PBE-60, B+ GSE-R, B+GSE-60). Each antioxidant group was further subdivided according to bonding time into 3 subgroups (immediate, 1-week, 2-week waiting period) after bleaching.
On immediate bonding, no bleaching group (NB) showed the highest mean value for microshear bond strength followed by groups treated with preheated extracts, followed by groups treated with non-preheated extracts and finally, the bleaching only group showed the lowest mean value.
However, on delayed bonding, no bleaching group together with groups treated with preheated extracts showed the highest bond strength values with no significant difference between them.
In all bonding times when preheated antioxidants were used after bleaching and prior to bonding, they resulted in significantly higher bond strengths values than non-preheated, this was confirmed by DPPH results.
No significant difference in bond strength values was obtained among the 1-week and 2-week delayed bonding.
Under limitations of this study, we can conclude that the application of preheated antioxidants combined with delayed bonding to tooth surfaces after bleaching can scavenge the residual oxygen species and hence increase the lowered DC and µSBS values back to the level of unbleached bond strength.