Abstract: Objective:To test differences of different thickness of PermaCem-Dual on the effect of Crown’s Retention. Methods: 30 extracted human maxillary premolars were selected for orthodontics purpose and randomly divided into three groups, tooth structure was prepared according to uniform standards，the metal crowns were produced and the adhesive thickness were Group A、Group B、Group C, ten of each group. All teeth were tested for tensile strength after cyclic loaded by increasing Ladder-type load 10000 times.The data was analysised with SPSS 16.0 on single-factor analysis of variance (ANOVA) and SNK test between groups.Results: the tensile bonding strength of Group A was significantly greater than Group B and Group C，the difference was significant .(P <0.05). Conclusion: As the bond thickness increases, the tensile bond strength was decreased.

Key words: PermaCem-Dual, Adhesive thickness, Cyclic loading, Tensilebonding strength, Retention