Isfahan University of Medical SciencesDental Research Journal1735-33274120080120The Effect of Fluid Composite as Gingival Layer on Microleakage of Class II Composite Restorations4848M.Sadeghi. mostafasadeghi@yahoo.com20101106Introduction Fluid composites have been suggested as gingival layer beneath class II composite restorations to improve marginal integrity and reduce microleakage. This in-vitro study evaluated the influence of fluid composites as gingival layer on microleakage of class II packable, microhy-brid, and fiber-reinforced composite restorations with the margins below the cementoenamel junc-tion (CEJ). Methods and Materials 45 sound premolars extracted for orthodontic reasons were selected. Class II cavities were prepared on the mesial and distal aspects with the gingival margin placed 1 mm be-low the CEJ, making 90 slot cavities. Teeth were randomly assigned into 3 groups (n=15). In each group, one side of each tooth was restored incrementally with respective packable, microhybrid, and fiber-reinforced composites; whereas, on the other side, fluid composite was placed as a 1 mm thickness gingival increment before restoration with the same composites. The teeth were stored for one week in distilled water at 37ْ C, thermo-cycled (5-55ْ C, x 1500), and immersed in 0.5% basic fuchsine for 24 hours. Dye penetration was evaluated using a stereomicroscope at 10x magnification. The data were analyzed statistically by Kruskal-Wallis analysis of variance and Mann-Whitney U-test. Results The fluid composite reduced microleakage at gingival margins of Class II restorations (P