Method: One conventional GIC (Fuji IX GP, GC), and two resin modified (RM) GICs (Fuji II LC EM, Fujifil LC, GC) were used. Cements were hand mixed according to the instructions, inserted into the mold and a transparent matrix was added to give a smooth surface. For RMGICs, specimens were light irradiated for 20 s. Specimens were prepared and divided into three groups as follows: without pretreatment (control), 35% phosphoric acid etching for 15 s, and air-abrasion for 5 s. Adhesive was applied and resin composite was bonded. Ten specimens per group were tested in shear mode at a cross-head speed of 1.0 mm/min. The surface free energies of five specimens per group were determined by measuring contact angles. Data for each adhesive system were analyzed using Tukey’s HSD test.
Result: For conventional GIC, acid etching or air-abrasion increased bond strength (8.5-8.8 MPa) when compared with controls (4.7 MPa); however, RMGIC resulted in significantly lower bond strengths (10.3-15.8 MPa) than in controls (14.2-20.5 MPa). The value of the γS– component increased when conventional GIC was treated with phosphoric acid or air-abrasion (60.1-60.5 mJ·m–2) when compared with controls (52.8 mJ·m–2). For RMGICs, lower values of the γS– component were detected for the control group (12.7-16.0 mJ·m–2), indicating the presence of a resin-rich layer on the surface.
Conclusion: The surface treatment of the conventional GIC promoted higher bond strength to resin composite, but decreased bond strengths for RMGICs. RMGIC surfaces should be left untreated to obtain optimal bonding to resin composite, this is due to similar chemistry between RMGIC and the resin composite, which allows strong chemical bonding of RMGIC to the composite resin.