Abstract: Objective: To measure the microleakage of resin-restoration after chewing for half a year, and analyze the necessity of beveled margin using cyclic mechanical loading experiment. Methods: One hundred and forty fresh dissociated teeth were divided into 14 groups according to different cavity margin designs, different numbers of loading cycles (0 or 1×10⁵ times loading or 1.3×10⁶ times loading cycles), and different loading sites (the buccal cusp or the buccal interface or the restoration ). After all the cavities were filled with combined resins (3M FiltekTM P60) and entrapped, each sample received cyclic mechanical loading. Then all pieces were examined to observe the dye penetrated along the tooth-restoration interface. SPSS17.0 software was used for statistical analysis. Results: The microleakage of 1.3×10⁶ times loading group was larger than that of the 0 and 1×10⁵ times loading group. There was no significant difference among groups with beveled margin or not after 0 cyclic loading (P>0.05. After 1.3×10⁶ times loading, the microleakage of tooth loaded with beveled margin was less than that without beveled margin(P<0.05). Conclusion: After chewing for half a year, the beveled margin could reduce the microleakage of resin-restoration.

Key words: Cyclic mechanical loading , Microleakage, Beveled margin, Resin