الفهرس 
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Abstract
Objective: To evaluate the effect of immediate and delayed chemical activated bleaching on microleakage of class V resin composite restorations using three different types of adhesives: etch and rinse (E&R), self-etch (SE) and glass ionomer-based adhesives (GI). Materials and Methods: Sixty freshly extracted sound molars were selected. After disinfection; box-shaped cavity with butt joint cavo-surface margin was prepared on the buccal surfaces of each tooth with a mesiodistal width of 4 mm, occluso-gingival height of 3 mm and depth of cavity 2 mm. The cavities were placed with the occlusal margin located 1.5 mm coronal to the cementoenamel junction (CEJ), the dimensions of each cavity were measured with a periodontal probe to maintain uniformity. The 60 restorations were randomly divided into three groups, each group consists of 20 teeth (n=20), according to type of adhesive systems used, one group was treated with E&R adhesive, the second group with SE one step adhesive and the third treated with glass ionomer-based adhesive. All the adhesive systems and resin composite restorations were applied according to the manufacturer’s instructions then each group was divided into two subgroups regarding to time of bleaching, one of them was bleached immediately (immediate bleaching) and the other stored in artificial saliva for 3 months, then it was bleached (delayed bleaching). All the specimens were placed in crystal violet dye for 24 hours, washed and sectioned by a disc buccolingually, restoration margins either enamel (occlusal margin) or dentin (gingival margin) were examined under stereomicroscope. All the collected data were tabulated and statistically analyzed for variables using Three-way ANOVA, Paired sample t-test, Independent sample t-test and One-way ANOVA followed by Tukey post hoc test were used for multiple comparison. Results: A significant difference for variables was revealed by Three-way ANOVA (p<0.001). Paired sample t-test showed a significant difference between occlusal and gingival margins, the highest mean value for all groups was found in gingival margins, while the least one value was recorded in occlusal margins. Independent sample t-test indicated that, the highest mean value for all sub-groups was found in immediate sub-groups, while the least one was recorded in delayed sub-groups. One-way ANOVA followed by Tukey post hoc test exhibited a significant difference, the highest mean value was found in (E&R) groups followed by (SE), while the least mean value was recorded in (GI based adhesive) groups. Conclusion: Based on results of this study, and despite of the limitation of small sample size, it seems reasonable to conclude that: 1- Bleaching on resin composite restorations is more conservative and non-invasive procedure to tooth structure to harmonize and match the shade of composite restorations with the natural color of teeth instead of more preparations in tooth structure to make a new composite restoration. 2- Delayed bleaching for resin composite restoration was preferred than immediate bleaching. 3- Using glass ionomer-based adhesives provided more favorable internal adaptation compared to etch and rinse and self etch adhesives. Bonding to enamel is better than bonding to dentin.