Does Composite Repair Time Affect Repair Protocol, Immediate or Delayed?

Abstract Background: Composite resin restorations frequently require repair due to fractures, marginal defects, or esthetic failures. The effectiveness of composite repair depends heavily on the surface treatment applied prior to bonding. This study aimed to evaluate the effects of various surface treatment protocols on the shear bond strength(SBS) between composite resin layers in same-visit immediate repair and delayed repair conditions, using bulk-fill and nanohybrid composite resins. Methods: Two types of composite resin materials—NeoSpectra ST HV (nanohybrid) and Tetric N-Ceram Bulk-Fill—were tested. A total of ten surface treatment protocols were evaluated under both immediate and delayed repair conditions (n = 10 per subgroup). Following grinding with a diamond bur, the surfaces were treated with one of the following: phosphoric acid, universal adhesives (Single Bond Universal, Prime&Bond Universal), three application modes of Clearfil SE Bond (two-step, bond only without primer, or phosphoric acid application followed by bond only), Optibond FL without primer, or GC Modeling Liquid. Additionally, direct layering without any surface treatment was included as a control. SBS was measured using a universal testing machine, and failure modes were analyzed using a stereomicroscope. One-way analysis of variance and Tukey’s post hoc test were used for statistical analysis (p = 0.05). Results: Immediate repair groups showed significantly higher SBS than DR groups across both composite types. The highest SBS were observed with GC Modeling Liquid and hydrophobic bonding agents, particularly in the bulk-fill immediate repair groups. Phosphoric acid application alone, or in combination with self-etch adhesive, did not improve bond strength. Universal adhesives did not outperform hydrophobic agents in any condition. Direct layering without treatment resulted in the lowest bond strength, especially in delayed repair. Conclusions: Surface treatment protocol significantly affects the success of composite resin repair. Hydrophobic adhesives and GC Modeling Liquid proved to be the most effective options, especially for same-visit immediate repairs. Simplified approaches avoiding unnecessary etching or priming may offer clinically efficient solutions without compromising bond strength.