Purpose: To assess the microtensile bond strengths of a core composite with two different viscosities, MultiCore Flow (F) and Heavy Body (HB) (Ivoclar-Vivadent), on dentin and glass-fiber posts with methacrylate resin matrices, in combination with three dentin adhesives: Syntac Classic (S), Excite DSC (E), and AdheSE (A) (Ivoclar-Vivadent). The omission of an intermediate adhesive coating on silanized posts was also examined to see if this resulted in post-core bond strength reduction. Materials and Methods: Six experimental dentin and 6 experimental post groups were formed with different core material viscosity/adhesive combinations. In two control post groups, no adhesive was applied on the silanized posts. The core material was stratified on deep dentin or on the posts. From the built-up teeth and the post-core units, microtensile sticks were obtained. Results: The bond strengths measured on dentin were (MPa): S-F 12.7 ± 6.4; S-HB 18.3 ± 7.6; E-F 33.1 ± 13.7; E-HB 34.1 ± 10.2; A-F 33.5 ± 14.8; A-HB 35.5 ± 14.4. The post-core strengths were: S-F 9.4 ± 2.5; S-HB 7.1 ± 3.8; E-F 8.6 ± 3.8; E-HB 8.1 ± 4.4; A-F 8.1 ± 2.7; A-HB 8.3 ± 2.4; no adhesive-F 10.4 ± 3.6; no adhesive-HB 6.3 ± 2.7. Significantly higher interfacial strengths were achieved on dentin than on posts (p < 0.05). Adhesive type significantly affected core-dentin adhesion, with Excite DSC and AdheSE outperforming Syntac Classic (p < 0.05). Neither core material viscosity nor adhesive type significantly influenced post-core adhesion (p > 0.05). Omission of an intermediate adhesive layer had no effect on post-core adhesion (p > 0.05). Conclusions: Even after post surface silanization, the bond established by the composite core material with the post remains weaker than that created with coronal dentin.

Keywords: composite resin, core, fiber post, dentin, bond strength