Objective: To determine the effect of two different composite resins by using different filling techniques through measuring the gingival microleakage in class II cavity. Materials and methods: Standardized 80 class II cavities were prepared in the proximal surfaces of forty extracted non caries permanent molars and randomly were divided into two main groups (A and B) 40 cavities for each group. In group A the Nanohybrid resin based composite was used and for group B, Microhybrid resin based composite was used, then each main group was subdivided into four subgroups (n=10 cavities) according to the composite placement technique: 1) bulk, 2) vertical, 3) split horizontal and 4) centripetal. The specimens were immersed in a solution 2% methylene blue dye for 24hours. The microleakage scores (0 to 3) were obtained from the cervical surface and the cervical microleakage was analyzed with a stereomicroscope. Results: The gingival microleakage is less in nanohybrid group than in microhybrid, in both groups the worst result is in bulk technique followed by vertical, split horizontal and/or centripetal techniques. Conclusion: This study predicts that the Nanohybrid resin based composite is better than Microhybrid resin based composite for posterior class II restoration. Also centripetal and split horizontal are better than vertical layering and bulk techniques.
