Objective The purpose of this in vitro study was to research the influence of cyclic loading and luting agents on microleakage of cast crowns and to determine the ability of four luting agents to resist microleakage. Methods 20 recently extracted premolars were divided equally into four groups of four luting agents. All teeth were prepared with the preparation criteria. After full cast crowns were fabricated, they were cemented. Specimens of the four group were subjected to 300 000 cyclic loadings in a chewing simulator and 5 000 thermal cycles（5 °C and 55 °C）. Subsequently, all specimens were placed in a dyeing solution and then vertically cut in mesiodistal direction. The objects were evaluated for microleakage using a microscope camera. Finally, the level of microleakage of each group was scored and analyzed. Results This study found that after cyclic loading and thermal cycles, there are significant differences between four groups, and resin cement has the lowest level of microleakage. Cyclic loadings and thermal cycles increased significantly microleakage of crowns with four different luting agents. Conclusion After cyclic loadings and thermal cycles, cast crowns cemented with resin cement have demonstrated the best performance to resisit microleakage, which implies that for metal crown and metal inlay, resin cement should have priority to be chosen by dental practitioners.
