Abstract: 〗［Abstract］ Objective〖HTSS〗〓To evaluate and compare the resistance level of fullcontour zirconia crowns under cyclic loading.
〖HTH〗〖WTHZ〗Methods〖HTSS〗〓A computer aided design and computer aided manufacturing(CAD/CAM) system was used to prepare 18 fullcontour zirconia crowns of the mandible first molar. All the crowns were bonded to the metal dies using 3M glass ionomer cement and were randomly divided into A, B, C groups, each group with six. Group A and group B was respectively fixed on the biomechanical test machine for cyclic loading, with a frequency of 8 Hz, 300 000 cycles.The loading force of group A was 300 N,and group B was 500 N. The compressive strength were measured by the universal testing machine. Used SPSS 21.0 software to analyze the data.
〖HTH〗〖WTHZ〗Results〖HTSS〗〓There were no statistical significant differences between two groups(P＞005).
〖HTH〗〖WTHZ〗Conclusion〖HTSS〗〓Using different force  for 300 000 cycles on the zirconium crown load had no significant effect on its resistance to compressive strength.

Key words: tooth crown, zirconia, compressive strength, cyclic loading