Tehran University of Medical Sciences Frontiers in Dentistry 2676-296X 15 4 2018 08 19 240 249 EN Sayed Mostafa Mousavinasab Professor, Dental Materials Research Center, Department of Operative Dentistry, School of Dentistry, Isfahan University of Medical Sciences, Isfahan, Iran Maede Ghasemi Assistant Professor, Dental Materials Research Center, Department of Operative Dentistry, School of Dentistry, Isfahan University of Medical Sciences, Isfahan, Iran Mitra Yadollahi Assistant Professor, Department of Operative Dentistry, School of Dentistry, Shahrekord University of Medical Sciences, Shahrekord, Iran 2017 12 26 2018 05 16 Objectives:The aim of this study was to evaluate enamel and dentinal microleakage in Class II cavities restored with silorane- and methacrylate-based resin composites using specific and nonspecific adhesives. Materials and Methods: Thirty-six caries-free human premolars were used. Two Class II cavities were prepared on each tooth. The gingival floor was set at 1 mm above (on the mesial surface) and at 1 mm below (on the distal surface) the cementoenamel junction (CEJ). The samples were randomly divided into four groups, and the cavities were restored with a methacrylate-based composite (Filtek™ P60) and a silorane-based composite (Filtek™ P90) with specific and nonspecific adhesives. Microleakage was tested using a standardized dye penetration method. All samples were examined under a stereomicroscope, and microleakage scores were statistically analyzed using Kruskal-Wallis and Mann-Whitney-U tests. One sample from each group was examined under a scanning electron microscope (SEM) to determine the bonding area. Results: No significant difference was found between the groups in terms of the enamel microleakage (P=0.086). There was a significant difference between the groups with regard to dentinal microleakage (P=0.003). No significant reduction in microleakage was observed in groups restored with Filtek™ P90 composite using its specific adhesive compared to those restored with Filtek™ P60 composite using its specific adhesive (P=0.626). Conclusions: The results indicated that the application of methacrylate- and silorane-based composites with specific or nonspecific adhesives had no impact on enamel microleakage, but it affected dentinal microleakage, and specific adhesives showed less microleakage. It seems that a phosphate-methacrylate-based intermediate resin is required to bond dimethacrylate adhesive to silorane-based composites. https://fid.tums.ac.ir/index.php/fid/article/view/2301 https://fid.tums.ac.ir/index.php/fid/article/download/2301/1017