الفهرس 
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Abstract
Dissertation Abstract : Purpose: To evaluate the effect of water storage on μTBS and nanoleakage of the contemporary universal adhesive systems applied to dentin under different modes compared to 2-step SE adhesive. Materials and Methods: Ninety eight sound human molars were assigned into main four groups of 28 teeth each except the control group 14. After disinfection, they were fixed in self-cure acrylic resin. Flat dentin surface were exposed using a diamond saw. A standardized smear layer was formed by 600-grit silicon carbide paper under running water. Teeth were randomly divided into four main groups related to the adhesive system used; one 2-step SE adhesive as a control group (OptiBond XTR), and three universal adhesives (G-Premio BOND, SINGLE BOND, and TETRIC N BOND) were used in the study. Then, each group of universal adhesives was subdivided into two subgroups according to the philosophy of dealing with the smear layer; either E&R or SE approach. A nano-filled resin composite block built up over the dentin surface incrementally (each increment one mm thickness) using a metal band forming a mold of 4 mm height, 4 mm length and 4 mm width. Specimens of each universal adhesive subgroup and 2-step SE group were assigned into two divisions according to the time of water storage into: immediate (24h) and delayed (6 months). Each specimen was sectioned into a series of 1 mm thick beams to produce dentin-resin composite beams. A universal testing machine was used for applying tensile load using a cross-head speed of 0.5 mm/min, until failure of the bond through the specimen occurs. The failure mode was analyzed using Stereomicroscope and selectively specimen from each mode was inspected using SEM. SEM was used to detect interfacial nanoleakage of adhesive surface. Finally, the collected μTBS data was statistically analyzed for variables by two-way analysis of variance (ANOVA). Student’s t-test and one-way ANOVA with Tukey’s post-hoc tests were used for multiple comparisons. The level of significance was adjusted at (p<0.05).