Effect of an Adhesive-Enhancing Primer on Shear Bond Strength in Repairs of Fresh Resin Composite to Aged Resin Composite: With and Without Saliva Contamination

The objective was to investigate the effect of an adhesive-enhancing primer (AEP) on the shear bond strength (SBS) between fresh resin composite and aged resin composite interface, specifically considering the presence or absence of saliva contamination on the aged resin composites. One hundred fifty-three resin composite blocks underwent thermocycling to replicate aging. Nine groups (n = 15) formed: Group 1: no saliva + no surface treatment; Group 2: no saliva + AEP; Group 3: no saliva + bonding agent; Group 4: no saliva + AEP + bonding agent; Group 5: saliva + no surface treatment; Group 6: saliva + AEP; Group 7: saliva + bonding agent; Group 8: saliva + AEP + bonding agent; and Group 9: saliva + phosphoric acid + bonding agent. Fresh resin composite was applied to the surface of each sample and then light-cured. All specimens were stored for 24 h in distilled water at 37 °C. The SBS testing and failure modes were assessed next. One-way ANOVA and the Tukey test (α = 0.05) were used. Group 9 had the highest SBS (15.42 ± 1.37 MPa) but did not significantly differ from Groups 3, 4, 7, and 8 (p > 0.05). Group 5 showed the lowest SBS (3.08 ± 0.41 MPa). Additionally, group 1 demonstrated significantly lower SBS than all other groups except group 5 (p < 0.001). Groups 2 and 6 exhibited comparable SBS (p > 0.05). Groups 3, 4, 7, 8, and 9 displayed both adhesive and mixed failure, whereas the other groups demonstrated a complete adhesive failure. Regardless of saliva contamination, AEP improved the bond strength at the interface between the fresh resin composite and the aged resin composite.