Effect of resin cement, aging process, and root level on the bond strength of fiber-posts: An in vitro study

To compare the push-out bond strength (POBS) of two resin cement systems (total-etch versus self-etch) for cementing FRC (fiber-reinforced composite) posts in three different thermocycling aging periods (40,000; 20,000; and none) using thermocycling and three root levels (apical, middle, and coronal).

60 bicuspid single rooted natural teeth were endodontically treated and post spaces were prepared to receive a fiber-post (RelyX FiberPost) cemented with either total-etch (RelyX Ultimate) or self-etch (RelyX Unicem) cement. Teeth were randomly allocated into six groups (n= 10): G1: Control (Ultimate without thermocycling); G2: Ultimate (20,000 cycles); G3: Ultimate (40,000 cycles); G4: Unicem without thermocycling; G5: Unicem (20,000 cycles); and G6: Unicem (40,000 cycles). POBS was determined by using a push-out test on a universal testing machine. Additionally, failure mode of each specimen was observed under a stereomicroscope at x40 magnification and scanning electron microscope (SEM) examination of selected samples. A nested general linear model was created for statistical significance P< 0.05. Post-hoc tests were carried out using pair-wise comparisons with a Bonferroni adjustment.

No significant differences were found on the bond strengths between the resin cements (P= 0.856). Regarding aging effect, bond strengths of the 40,000 cycle groups (G3/G6) were significantly lower than 20,000 cycle groups (G2/G5). In addition, the POBS of the specimens collected from the coronal third of the roots were significantly lower than specimens from the apical third regardless of the type of cement used. Regarding types of failures, adhesive failure (post/cement) was significantly higher in total-etch groups (G1-G3) than the self-etch groups (G4-G6). Adhesive failure (dentin/cement) was significantly higher in self-etch groups than the total-etch groups.

Within the limitations of this study, the bond strength to root canal dentin of self-etch and total-etch cements demonstrated reliable results and was not affected by the type of resin cement. Simplification of technique is an evident advantage of these materials in clinical practice.