Abstract
Abstract 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 transform infrared spectroscopy, varied between 22% and 42%, with a linear decrease in conversion associated with increased concentration of acidic methacrylate (R2 = 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.
Highlights
The longevity of dental composite resin restorations depends on a number of factors related to the restored teeth, restorative technique, and restorative materials
Formulation of the experimental repair primers Methacrylate-based repair primers were formulated by mixing the monomers urethane dimethacrylate (UDMA) and 2-hydroxiethyl methacrylate (HEMA), from Esstech Inc. (Essington, PA, USA), with the acidic monomer 1,3-glycerol phosphate dimethacrylate (GDMA-P), and the silane coupling agent 3-(trimethoxysilyl)propyl methacrylate
The orifices were filled with fresh composite resin (Opallis) to simulate the repair procedure and covered with a polyester strip and a glass slide
Summary
The longevity of dental composite resin restorations depends on a number of factors related to the restored teeth, restorative technique, and restorative materials. For many years, when the restorative material failed, the usual treatment indicated was complete replacement of the restoration using fresh composite resin [3]. Other treatments have been indicated as alternatives to the complete replacement of failed restorations, such as restoration repair or refurbishing. Whereas replacement of existing restorations is defined by complete substitution of the restorative [8], the repair procedure consists in removing only the defective portion of the composite and replacing it with fresh material. It has been reported that repairs might increase the longevity of dental restorations [8,9] Another alternative is to refurbish the restoration, i.e., adding new material to the defective portion of the restoration without removing any existing portion of the restorative [10]
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