Statement of problem: Little is known about how various polymerization combinations of dual-polymerized adhesives and resin core foundation pastes affect dentin bond strength.
Purpose: This study examined the influence of different polymerization modes of dual-polymerized resin direct core foundation systems on dentin bond strength using bovine dentin.
Material and methods: Two commercially available dual-polymerized resin direct core foundation systems, Clearfil DC Core and UniFil Core, were studied. Bovine mandibular incisors were mounted in autopolymerizing resin and the facial dentin surfaces were ground wet on 600-grit SiC paper. Dentin surfaces were treated according to manufacturer's recommendations, and dual-polymerized adhesives were applied and dual-polymerized (control) or only chemically polymerized. The core foundation resins were condensed into the mold (4 x 2-mm) and were also either dual-polymerized or only chemically polymerized. Eighty specimens (n=10) were stored in 37 degrees C water for 24 hours, then shear tested at a crosshead speed of 1.0 mm/min in a universal testing machine. Fourier transformation infrared spectroscopy was used to measure the degree of conversion of dual-polymerized resin core foundation pastes with both modes of polymerization. One- and 2-way ANOVA, Tukey HSD tests, and Student t -tests were performed (alpha=.05).
Results: The highest mean bond strengths (+/-SD) were obtained when the adhesives and resin pastes were dual-polymerized for both core foundation systems (14.6 +/- 2.1 MPa for Clearfil DC Core, 15.6 +/- 2.2 MPa for UniFil Core). Chemical polymerization of dual-polymerized adhesives and resin pastes resulted in significantly lower bond strength (2.8 +/- 0.6 MPa for Clearfil DC Core, 8.1 +/- 2.2 MPa for UniFil Core) ( P <.001). The degree of conversion for the resin pastes decreased significantly ( P <.05) when only chemical polymerization was employed, from 81.5% to 76.1% for Clearfil DC Core and 86.7% to 81.2% for UniFil Core.
Conclusion: The data suggests that the dentin bond strengths of the dual-polymerized resin direct core foundation systems are highest when both adhesive and resin core paste are dual polymerized.