Bond strength of self-adhesive resin cements used for onlays luting

Objective: To evaluate strength of the interface on dentin by the Experimental luting (EL, Ivoclar-Vivadent), RelyX Unicem (RU, 3M ESPE), and Maxcem (M, Sybron-Kerr), applied under two standardized clinically seating pressures. Methods: composite overlays (Paradigm MZ100, 3M ESPE) were luted on coronal dentin surfaces of 12 extracted molars, which are randomly divided in three groups (EL, RU, M). Each group is divided in two subgroups depending on the different seating pressures applied. During the initial 5 min auto-cure period, a pressure of 20 or 40g/mm2 was maintained on the overlay. Curing was completed by light irradiation from the top of the overlay for 20 s. Microtensile sticks were obtained from the luted teeth. The Two-Way Analysis of Variance was applied with bond strength as the dependent variable, cement, and seating pressure as factors. The Bonferroni test was applied for post-comparisons among cements and between factors interactions. In all the analyses the level of significance was set at p<0.05. Results: The bond strengths (MPa) in dentin were: EL 20g/mm2 8,28±5,44, 40g/mm2 13.19±5,44; RU 20g/mm2 6.8±2.6, 40g/mm2 14.5±5.3; M 20g/mm2 4.1±1.8, 40g/mm2 5.2±1.6. The Two-Way ANOVA revealed that cement, seating pressure and the interaction between these factors significantly influenced bond strength (p<0.05). Significantly stronger bonds were established under the heavier seating pressure. With regard to the cement factor, RelyX Unicem and the Experimental luting agent achieved levels of adhesion significantly higher than Maxcem. Significant between factors interactions are reported in the Table. Conclusion: Interfacial strength self-adhesive dual-cure cements are enhanced if a seating force heavier than finger pressure is maintained throughout the initial autocure period. Table CEMENT SEATING PRESSURE Mean (MPa) s.d. Significance P<0.05 Experimental 20g/mm² 8.28 5.44 A,b 40g/mm² 13.19 5.44 A,a RelyX Unicem 20g/mm² 6.8 2.6 A,bc 40g/mm² 14.5 5.3 A,a Maxcem 20g/mm² 4.1 1.8 B,c 40g/mm² 5.2 1.6 B,c