Objective:To evaluate the effect of different timing of coronal preparation on the bond strength of fiber post after cementation and provide theoretical basis for clinical practice.Methods: A total of thirty-five freshly extracted mandibular premolars with single-root canal were collected

sectioned and endodontically treated.Following post space preparation

high-strength glass fiber posts(tenax fiber white)were luted by dual-curing core and resin cement(ParaPostR ParaCoreTM) and the cores were formed.Then the roots were divided into five groups randomly(n=7) and the tooth preparation was performed immediately

and at the 15th min

30th min and 24th hours after splicing in four groups respectively.The other group without tooth preparation served as control.Twenty-four hours later

the roots with cemented posts were sectioned into slices with 1mm thickness and the slices were classified as coronal

middle and apical section.The push-out strength was tested and the fiber post fracture modes were observed under an optical microscope.Results: The push-out strength of fiber posts significantly increased as the time to prepare increased.The push-out strength in the 24th h group was significantly higher than in the other three prepared groups(P<0.05)

and not significantly higher than in the control group(P>0.05).In the same tooth

the push-out strength at crown 1/3 was significantly higher than that of the apical 1/3(P<0.05).Conclusion:In order to obtain better retention

it is suggested to perform tooth preparation 24 hours after cementation

and pay more attention to crown 1/3.