الفهرس 
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Abstract
Aim : To evaluate microtensile bond strength and nanoleakage patterns of resin-dentin interface for three bulk-fill resin composites compared to conventional incremental-fill resin composite subjected to water aging for 6 months. Materials and Methods: A total of 72 freshly extracted permanent molars free from caries were used in this study. Standardized high c-factor class Ⅰ cavity 4×4 mm width with 4 mm depth was prepared for all molars. The teeth were divided into 4 groups according to the type of resin composite used (n=18); group R1 (control) was restored with conventional incremental-fill resin composite while the other 3 groups (R2, R3, R4) were restored with 3 different bulk-fill resin composites. Each group was further subdivided into 2 subgroups according to aging (n=9); one subgroup (A) was immediately tested after 24h of restoring the teeth. The other subgroup (B) was tested after 6 months storage in artificial saliva in an incubator at 37℃. Universal adhesive was used for all samples using selective enamel etching technique for 30 seconds. from each subgroup 7 molars were tested for μTBS. Composite-dentin beams with cross section (1×1 mm2) were prepared from each molar then μTBS test was performed for each molar which considered as unit of the study. μTBS data were statistically analyzed using normality tests, two-way ANOVA and multiple comparison post hoc tests. Failure patterns for all beams used in μTBS test were detected using steriomicroscope, tabulated and analysed. Additional 2 molars from each subgroup were prepared for nanoleakage observation and scanned by Scanning Electron Microscope (SEM) to detect and describe silver nitrate intake patterns along resin-dentin interface at different four levels of magnification. Results : Normality tests revealed that μTBS results followed normal distribution. Two-way ANOVA test revealed that μTBS values werenot significantly affected by the type of resin composites used in the study (p>0.05). However, it revealed that μTBS values were significantly affected and decreased by aging (p<0.05). Tukey post hoc multiple comparison test revealed that there was significant difference in μTBS values between immediate and delayed control subgroups (p<0.05). However it revealed no significant difference in μTBS values between immediate and delayed bulk-fill subgroups (p>0.05). Nanoleakage test revealed different patterns of silver nitrate intake identified in all subgroups within the resin-dentin interface in both hybrid and adhesive layers. Silver nitrate intake increased after aging. Conclusion : Bulk-fill resin composites obtained similar μTBS values in class Ⅰ high C-factor cavity as conventional incremental-fill resin composite. μTBS values reduction was observed after 6 months of aging. Clinical significance: Single increment-filling technique using bulk-fill resin composites in class Ⅰ high C-factor cavity did not reduce μTBS values after 24 hours. Also it obtained similar and comparable results to conventional resin composite and reduced operation time. All these factors make bulk-fill resin composites good choice for posterior teeth restorations.