الفهرس 
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Abstract
This study evaluated the effect of pulpal pressure and dentin depth on the quality of hybrid layer in vivo on dogs’ teeth to simulate the clinical situation where both factors apply together in the oral environment. Methods: Eight healthy dogs, aged between 12 and 18 months, with intact dentitions were used for the experimental work. A total of 48 teeth were available for study by using the six upper anterior teeth of each of the eight dogs used in the study. The 48 teeth included in the study were divided according to presence or absence of pulpal pressure (P) into two groups with 24 teeth in each group. P teeth with positive pulpal pressure and P teeth with no pulpal pressure. Each of these two groups was further divided into two subgroups, according to the cavity depth (D) they received where in D 1 a cavity depth of 1mm was performed while in D2 a cavity depth of 2mm was performed. The Class V preparations were then restored with micro hybrid composite restorative material in an incremental technique. Half of the samples, was left in the dogs’ mouths for 7 days ) while the other half was left for 30 days At the end of the experimental period, the dogs were euthanized by injecting an overdose of sodium thiopental. The anterior part of the upper jaw was sawed out of each dog’s mouth and the teeth were sectioned below the level of the cemento-enamel junction. The coronal portion of each tooth was then sectioned longitudinally through the restoration in a labiolingual plane to evaluate the resin-dentin interface. The ybrid layer along the interface between the restoration and dentin was >were then analyzed using a specialized software Results: Results of the study showed that the mean resin tag length value was higher in non-vital groups than that of vital groups with statistically .