الفهرس 
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Abstract
The present study was conducted in order to evaluate the microleakage of class V cavities restored with two different resin based composite systems (silorane based and methacrylate based composites) and the microtensile bond strength of the two adhesive systems to enamel and dentin.
For microleakage test, a total of 30 freshly extracted human mandibular first and second molar teeth were collected and all the teeth surfaces were cleaned. A non retentive rectangular box cavity was prepared on the buccal surface of each tooth with the following dimensions 3mm wide (mesio-distal diameter) and 2mm high (occluso-cervical diameter), where 1.5mm occlusal and 0.5mm gingival to the cement-enamel junction.
The specimens were equally divided into two main groups of 15 teeth in each (n=15), according to the restorative systems used (methacrylate based resin composite/its corresponding bond and silorane based resin composite/its corresponding bond). Application of the two adhesive systems and composites were carried out according to the manufacturer’s instructions in both groups. For proper contouring, a pre-constructed tin foil lined green compound impression of each tooth was applied to its proper place to the buccal surface to assure good pressure and complete adaptation of the material to the cavity walls.
Teeth were coated with utility wax then immersed in 2% methanol solution of Lishman dye for 24 hours. Each tooth was sectioned longitudinally in a bucco-lingual plane. Finally, the sections were examined at both occlusal and cervical margins by binocular stereomicroscope for dye penetration through the restoration/tooth structure interface, and were statistically analyzed by Chi-square test.
For µTBS test, a total of 60 freshly extracted human maxillary first and second molar teeth were collected. Each tooth was invested vertically in the center of poly vinyl chloride mounting cylinder of 1.8 cm diameter and 2 cm height filled with self-polymerizing acrylic resin. The teeth were randomly divided into two equally main groups: G1 (enamel) and G2 (dentin) of 30 teeth in each (n=30), designed for enamel and dentin microtensile bond strength testing respectively. Then each group was subdivided into two subgroups of 15 teeth in each (n=15), according to the type of composite restorative system used: SG1 (methacrylate based restorative system) and SG2 (silorane based restorative system).
For the G1, the most superficial portion of enamel on the buccal aspect of each tooth was removed by means of 180-grit wet sand paper in order to create a flat enamel surface with at least mesio-distal width of 5mm and without exposing the underlying dentin. For the G2, the occlusal one third of each tooth was removed perpendicular to the tooth long axis using a low speed diamond disc under water cooling to eliminate all the enamel remnants and expose a flat dentin.
Both the two types of adhesive systems were applied according to the manufacturer’s instructions to both E and D groups. 5x5 mm resin composite block was built on the buccal surface of each tooth in G1 and 4x4mm resin composite block was built on the flat dentin surface of each tooth in G2. All the specimens of both groups were sectioned into sticks of 1x1mm2 cross sectional area. Then the specimens were fixed into a universal tensile bond strength testing machine. The collected data (in MPa) of all groups were subjected to statistical analysis by two-way analysis of variance (ANOVA) then t-test. Modes of failure for the debonded specimens were evaluated using binocular stereomicroscope.