Ferrule Effect on Fiber-post Push-out Bond Strength After Mechanical Fatigue

Objectives: To evaluate the influence of ferrule effect and mechanical fatigue aging on glass-fiber post push-out bond strength (PBS) to root-canal dentin.
Methods: Thirty-two sound maxillary premolars were cut 2.0mm above (w/Fer = with ferrule) (n=16) or at the cemento-enamel junction (CEJ) (wo/Fer = without ferrule) (n=16), and endodontically treated. After 24h water storage at 37°C, post spaces were prepared at 10-mm depth from CEJ and glass-fiber posts (Exacto #1, Angelus) were cemented using dual-cured self-adhesive composite cement (RelyX Unicem 2, 3M Oral Care). Standardized cores were built-up using light-cured composite (Filtek Z250, 3M Oral Care) and prepared using a taper rounded shoulder diamond bur (#3069, KG Sorensen). Crowns were hand-made using self-cured acrylic resin (JET, Clássico) and cemented using the above-mentioned composite cement. Half of the specimens, both with (w/Fer+MecFat = with ferrule + fatigue) and without ferrule (wo/Fer+MecFat = without ferrule + fatigue), were subjected to 1,200,000 cycles of mechanical fatigue in a chewing simulator (Mechatronik), while the other specimens were stored in distilled water at 37°C for 1 week. All specimens were next horizontally sectioned into 1-mm-thick slices prior to the PBS test. Data were analyzed using two-way ANOVA followed by Tukey’s HSD test. Failure mode was assessed using SEM with the frequency distribution compared by chi-squared test (α=.05).
Results: The mean PBS (MPa±SD) were: w/Fer (14.5±2.7); wo/Fer (14.2±2.9); w/Fer+MecFat (10.4±2.9); wo/Fer+MecFat (6.9±1.7). Specimens not subjected to fatigue resulted in higher PBS (p<0.001). After fatigue, absence of ferrule resulted in significantly lower PBS (p<0.05). Most failures occurred at the dentin/composite cement interfaces, followed by mixed and fiber-post/composite cement interface failures. There was a significant increase of mixed failures for the “wo/Fer+MecFat” group (p<0.001).
Conclusions: Absence of ferrule in premolars restored with fiber posts resulted in lower PBS to root-canal dentin after mechanical fatigue aging.