Comparative Evaluation of Shear Bond Strength in Antimicrobial-Modified vs. Conventional Universal Adhesives Under Aging Conditions

Background: The incorporation of antimicrobial agents into universal adhesives (UAs) aims to reduce cariogenic bacterial activity while maintaining adequate bond strength. However, current evidence regarding their e@ectiveness remains inconsistent. Aim: To compare the shear bond strength (SBS) of antimicrobial-modified universal adhesives (AM-UAs) versus conventional universal adhesives under immediate and thermocycled conditions. Methods: Sixty freshly extracted, caries-free human third molars (providing 120 dentin surfaces) were randomly assigned into six groups (n = 20 surfaces per group). Three antimicrobial-modified UAs (Gluma 2 Bond, Excite, Dentsply Xeno) and three non-antimicrobial UAs (Gluma Universal, Tetric Universal, Dentsply Universal) were applied to dentin, followed by composite build-up. All specimens were stored in distilled water at 37°C for 24 hours. Half of the samples from each group (n = 10) were tested immediately for SBS, while the remaining samples (n = 10) underwent thermocycling (5–55°C, 10,000 cycles) before SBS testing. Data were analyzed using Three-Way ANOVA with a significance level of p < 0.05. Results: Gluma Universal (non-antimicrobial) exhibited significantly higher bond strength than Gluma 2 Bond (antimicrobial) after 24 hours (p < 0.001). No significant di@erences were found between Dentsply Universal vs. Dentsply Xeno or Tetric Universal vs. Excite (p = 0.10) at the immediate time point. After aging, antimicrobial systems Dentsply Xeno and Excite demonstrated significantly higher SBS compared with their non-antimicrobial counterparts (Dentsply Universal and Tetric Universal) (p = 0.01). Thermocycling increased bond strength across most groups (e.g., Gluma Universal: 10.01 MPa → 22.54 MPa), indicating enhanced aging resistance. Conclusion: This in-vitro study showed that incorporating antibacterial agents into universal adhesives did not significantly influence SBS under either immediate or thermocycled conditions. Although performance varied among brands, thermocycling consistently enhanced bond strength across all adhesives. Therefore, adhesive selection should be based on formulation-specific characteristics and documented clinical performance rather than the presence of antibacterial additives alone. Further in-vivo studies are recommended to validate long-term behavior in the oral environment.