Introduction: In spite of improvements in composite function, marginal microleakage in deep composite restoration is still considered as a challenge due to unstable bond between composite and dentin. Therefore, this study aimed to investigate effect of applying different materials on marginal microleakage in posterior composite restoration. Methods: A standard distal box was prepared on 80 human premolar. The gingival floors were 1 millimeter under CEJ. The specimens were divided to four groups. In the first group, 1 millimeter amalgam was used as the first increment in proximal box on gingival floor, in the second group flow able composite, and in the third group, RMGI were used. Other cavities were filled by condensable composite. In the fourth group (control), all the cavities were filled only by condensable composite. The specimens, after 6 months of storage, were placed under cyclic load (10000 cycle- 80 N- 1 Hz), and then were immersed in 2% methylene blue for 6 hours. Afterwards, the specimens were sectioned in the middle of restoration. Extension of dye penetration at the cervical margin was examined under a stereo microscope at 25x magnification and the leakage was evaluated by Fuks degree. The study data were statistically analyzed using the Mann- Whitney U-test (p<0.05). Results: Microleakage was observed in all the groups. The third group demonstrated the most leakage and the least was for the first group. No statistically significant difference was observed between the groups. )p-value =0.689) Conclusion: In cavities with gingival floor under CEJ, different filling methods have no effect on marginal sealing.

Keywords: Amalgam, Composite, Gingival Margin, Microleakage, RMGI

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