Effect of nano silver fluoride pre-treatment on the microtensile bond strength of a universal adhesive to dentin: an in vitro study

Objective: The study aims to evaluate the effect of Nano Silver Fluoride (NSF) pre-treatment at two concentrations on the microtensile bond strength (µTBS) of a universal adhesive to dentin. Methods: Flat deep coronal dentin surfaces from sound human molars were treated with NSF at 600 or 1500 ppm, or left untreated (control). A universal adhesive (Single Bond Universal; 3M ESPE/now Solventum) was applied in self-etch (SE) mode, followed by placement of a bulk-fill resin composite (Filtek Bulk Fill; 3M ESPE / now Solventum). Specimens were sectioned to obtain sticks (~1 mm2) and tested for µTBS using a universal testing machine (500 N load cell; 5 mm/min crosshead speed), considering the tooth as the experimental unit (n = 8). Group comparisons were performed using Welch’s one-way Analysis of Variance (ANOVA). Weibull analysis was conducted on stick-level data (n = 56 per group) to assess bond strength reliability. Failure modes were evaluated under stereomicroscopy, and dentin morphology and silver nanoparticle distribution were qualitatively assessed using Scanning Electron Microscopy (SEM). Results: No statistically significant differences were detected among groups (p = 0.074). Mean µTBS values were 33.0 ± 10.2 MPa (control), 35.6 ± 8.7 MPa (NSF 600), and 21.4 ± 11.7 MPa (NSF 1500). Effect size analysis indicated a large effect associated with NSF concentration. Weibull analysis showed lower characteristic strength and Weibull modulus for the NSF 1500 group, indicating reduced bond reliability. Adhesive failures predominated in all groups. Conclusion: Although no statistically significant differences were detected, higher NSF concentration (1500 ppm) was associated with lower bond strength reliability, whereas the lower concentration (600 ppm) maintained favorable bonding performance. Greater accumulation of silver nanoparticles on the dentin surface may interfere with resin infiltration and hybrid layer formation.