In this study, experimental resin-based primers with varying concentrations of acidic methacrylate were formulated and tested as to their potential in improving the repair bond strength of an aged dental composite resin. The photocurable primers contained (wt%) methacrylate monomers (20-60%), acidic methacrylate (0-40%), silane coupling agent (10%), and ethanol (30%). The pH of the solutions varied between 4.8 and 0.31. The degree of C = C conversion of the primers, measured using Fourier

more »

... orm infrared spectroscopy, varied between 22% and 42%, with a linear decrease in conversion associated with increased concentration of acidic methacrylate (R 2 = 0.961; p < 0.01). Composite resin blocks aged using 1000 thermalcycles served as substrate for the repair bond strength test. The primers were vigorously applied to the composite surfaces and a silicone mold with cylindrical orifices was placed onto the surface. The orifices were filled with fresh composite resin (simulating the repair). In the control group, no primer was applied. A shear bond test was conducted after 24 h (n = 16 per group). Failure modes were classified under magnification. Data were statistically analyzed at p < 0.05. Repair bond strength values varied between 7.2 and 26.5 MPa. The control group had lower bonding ability than all primed groups. The increased content of acidic methacrylate had no significant association with bond strengths. In the control group only interfacial failures were detected, whereas cohesive failures within the aged composite were observed in the primed groups. In conclusion, application of methacrylate-based primers might improve the repair bond strength of dental composite resins. The concentration of acidic methacrylate on the primer had no significant effect on the immediate repair potential.