الفهرس 
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Abstract
144 non carious, extracted human teeth were used in this study, 24 teeth were selected for demonstrating the adhesive resins’ infiltration through the dentinal substrate, using scanning electron microscopy. The remaining 120 teeth were used for evaluating the shear bond strength of composite resin to dentin.
All teeth were divided into four groups to represent four different surface substrate inclinations.
Shear bond strength testing : Analysis of variance (ANOVA) test was performed to assess the presence of significant differences in mean shear bond strengths at different surface substrate inclinations (whether the different inclinations of surface substrate produced significant effect on the mean shear bond strengths).
Student-Newman-Keuls test and the least significant difference procedure were used for pair wise comparison between means to find out which means were significantly different.
The above tests were separately performed for the groups of specimens that were immediately investigated; those that were stored for one week & those that were stored for one month and for both adhesive systems used.
ANOVA test, also, was performed to study the effect of time on the shear bond strengths of all groups of specimens at each substrate inclination through all time periods; for each adhesive system.
Finally, Student’s t-test was used for comparison between the mean shear bond strengths of the two adhesive systems used; at different substrate inclinations and at all time intervals (T0, T1, T2).
SEM : Analysis of variance (ANOVA) test was performed to assess the presence of significant differences in mean hybrid layer thicknesses at different surface substrate inclinations.
Student-Neuman-Keuls test and the least significant difference procedure were used for pair wise comparison between means to find out which means were significantly different.
The above tests were separately performed for each adhesive system.
Then, Student’s t-test was used to compare the mean thicknesses of hybrid layers of the two adhesive systems used, at different surface substrate inclinations.
Results : For both adhesive systems, and within each time period, the results revealed that different inclinations of surface substrate produced statistically significant changes in the mean shear bond strengths, as well as, hybrid layer thicknesses (P < 0.001). The mean shear bond strengths of the group of specimens to which the application of the adhesive system was performed with the occlusal plane of the lower jaw of the phantom head parallel to the floor (group A4), were significantly higher than the other 3 groups (P < 0.05). That group of specimens also demonstrated the thickest hybrid layers compared to the other 3 groups.
group A2 (the group of specimens to which the application of the adhesive system was performed with the occlusal plane of the upper jaw of the phantom head making a forty five degree angle with the floor), came next despite the fact that SEM micrographs of specimens belonging to that group demonstrated relatively thin hybrid layers. The ranking of groups according to the mean shear bond strengths was : A4 > A2 > A1 > A3.
There was no relationship between bond strength and the thickness of the hybrid layer.
Regarding the effect of storage time (one week and one month) on the mean shear bond strengths of both adhesive systems, it was found that there were no significant differences among the shear bond strengths of any of the two adhesive systems used, at any substrate inclination, through all time periods (T0, T1, T2) (P > 0.05).