Microtensile bond strength and interfacial properties of self-etching and self-adhesive resin cements used to lute composite onlays under different seating forces

Purpose: To evaluate strength and morphology of the interface created on enamel and dentin by Panavia F 2.0 (P, Kuraray), RelyX Unicem (RU, 3M ESPE), and Maxeem (M, Sybron-Kerr), applied under two standardized clinically realistic seating pressures. Materials and Methods: Composite overlays (Paradigm MZ100, 3M ESPE) were luted on flat enamel or dentin surfaces of 48 extracted molars. During the initial 5-min self-curing period, a pressure of either 20 or 40 g/mm2 was maintained on the overlay. Curing was completed by light irradiation from the top of the overlay for 20 s. Microtensile sticks and specimens for SCM observations were obtained from the luted teeth. Bond strength data from enamel and dentin (MPa) were analyzed with separate two-way ANOVAs in order to assess the effect of cement type, luting pressure, and their interactions. Tukey's test was used for post-hoc comparisons (α = 0.05), Results: The bond strengths (MPa) to dentin were: P 20 g/mm2 7.5 ± 3.7, 40 g/mm2 10.9 ± 4.5; RU 20 g/mm2 6.8 ± 2.6, 40 g/mm2 14.5 ± 5.3; M 20 g/mm2 4.1 ± 1.8, 40 g/mm2 5.2 ± 1.6. The bond strengths (MPa) to enamel were: P 20 g/mm2 25.2 ± 9.0, 40 g/mm2 30.7 ± 8.6; RU 20 g/mm2 10.7 ± 4.9, 40 g/mm2 11.1 ± 5; M 20 g/mm2 7.3 ± 3.1, 40 g/mm2 7.9 ± 3.2. Cement type, luting pressure, and the interaction of these two factors had significant influences on dentin bond strength, with RU and P outperforming M. RU and P significantly benefited from the increase in luting pressure. In enamel, the type of cement was a significant factor for adhesion, with P yielding the highest and M the lowest strength. The measured bond strengths corresponded with the morphological results. Conclusion: Interfacial strength and adaptation of self-etching and self-adhesive dual-curing cements are enhanced if a seating force greater than finger pressure is maintained throughout the initial self-curing period.