Bond Strength of Fiber Posts to Adhesively Restored Intracanal Dentin

Objectives: This ex vivo study evaluated the influence of different light-exposure times on the interfacial bond strength of fiber posts (DT Light Post, Bisco Inc.) to experimentally weakened root dentin restored with composite resin (Light Core, Bisco Inc.).

Methods: Sixty 17-mm long maxillary incisor roots were used. Twenty-four hours after obturation, the root canals were emptied up to a depth of 12 mm and 4 groups (n=15) were formed at random. In the 3 experimental groups (G1, G2 and G3), root dentin was flared to produce a 1-mm space between the fiber post and the canal walls. In the control group (G4), the roots were not experimentally weakened. The roots in the experimental groups were bulk restored with Light Core composite resin, which was light-activated through the DT Light Post for either 40 s (G1), 80 s (G2) or 120 s (G3). The posts were cemented (Duo Link-Bisco Inc.) and, after 24 h, the roots were sectioned transversely at the coronal, middle and apical regions producing 1-mm-thick slices (±0.1 mm). Push-out tests were performed (0.5 mm/min, Instron 4444) and failure modes were observed under stereomicroscopy.

Results: Means in MPa (±SD) were: GC=7.939 ±2.784; G1=10.36 ±2.99; G2=9.03 ± 2.69 and G3=10.28 ±3.16. Two-way ANOVA (a=0.05) indicated statistically significant difference among the groups (p<0.001), but not among the post regions (p>0.05). Comparing the weakened/reinforced groups, composite light-exposure time did not influence the results (p>0.05). There were a higher percentage of adhesive failures (in the post or dentin) in the control (73.33%) and experimental groups (85.18%). Cohesive failures occurred only in the weakened/reinforced roots (100%).

Conclusions: Root reinforcement with composite resin and light transmitting posts provided higher bond strength to dentin than the control group, independently of the composite light-exposure time and analyzed region.