Influence of Insertion Techniques for Resin Cement and Mechanical Cycling on the Bond Strength Between Fiber Posts and Root Dentin

Purpose: To evaluate the effect of the insertion technique for resin cement and mechanical cycling on the bond strength between fiber posts and root dentin. Materials and Methods: Sixty-four single-rooted bovine teeth were endodontically prepared to receive glass-fiber posts. The insertion of cement into the root canal was performed using one of the following techniques: POS, insertion with the post; LEN, the use of a lentulo-type drill; EXP, insertion with a straight-tip explorer; or CEN, the use of a Centrix syringe. Half of the specimens were mechanically cycled. All specimens were sectioned into slices of 1.8 mm for the push-out test and 0.5 mm for analysis of the cement layer quality. Results: The insertion technique affected the interaction between factors (bond strength and mechanical cycling; p 0.0001). Insertion of the Centrix syringe after mechanical cycling showed the highest bond values (13.6 ± 3.2 MPa). Group-to-group comparisons for baseline and cycled conditions indicated that mechanical cycling significantly influenced the bond strength (p 0.0001) of the POS and CEN groups. The quality of the cement layer did not differ between the techniques when evaluated in the middle (p = 0.0612) and cervical (p = 0.1119) regions, but did differ in the apical region (p = 0.0097), where the CEN group had better layer quality for the two conditions tested (baseline and cycled). Conclusion: The use of the Centrix syringe improved the homogeneity of the cement layer, reducing the defects in the layer and increasing adhesive strength values to dentin, even after mechanical cycling. Keywords: fiber post, cement layer, interface, adhesion, retention, mechanical loading, fatigue