The effect of pre-treated nano silver fluoride (NSF) on the microtensile bonding strength (MTBS) of composite resin to primary molars' dentin: an in-vitro study

Nanosilver fluoride (NSF) is an emerging anti-caries material that has garnered considerable attention in the field of dentistry due to its potent antimicrobial properties and its capacity to prevent dental caries—capabilities that have been significantly enhanced through advancements in nanotechnology. One of the notable advantages of NSF is its ability to remineralize dentinal carious lesions without causing the undesirable dark staining commonly associated with silver diamine fluoride. Despite its promising antimicrobial and remineralizing effects, there remains a paucity of comprehensive research investigating its influence on the mechanical properties and structural integrity of dentin, particularly in the context of adhesive restorative procedures. The present study aims to compare the physicochemical characteristics of NSF synthesized via a chemical method with those of a commercially available NSF formulation, and to evaluate the effect of NSF pre-treatment on the microtensile bond strength (mTBS) of composite resin to primary tooth dentin. In the chemical synthesis method, silver nitrate was combined with chitosan, followed by titration with sodium borohydride, and subsequently mixed with sodium fluoride. In contrast, the commercial preparation involved mixing colloidal silver with sodium fluoride and stirring until a homogeneous solution was obtained. Both formulations were stored in light-proof brown bottles to prevent photodegradation. For microtensile bond strength testing, forty-six extracted primary molars were sectioned buccolingually, with each half assigned to either the control group (without NSF pre-treatment) or the experimental group (with NSF pre-treatment). Following standard composite resin application protocols, the specimens were subjected to microtensile testing using a universal testing machine (UTM). The peak force at fracture was recorded, and the mTBS values were analyzed using a paired samples t-test to determine statistical significance. Additionally, the surface morphology and failure modes were examined using scanning electron microscopy (SEM). The results demonstrated that chemically-synthesizer NSF exhibited superior optical and structural properties, including a distinct surface plasmon resonance (SPR) peak at 410 nm and well-dispersed nanoparticles. Conversely, the commercial NSF lacked a defined SPR peak and predominantly existed in ionic form. The mTBS results indicated that the NSF-treated group (62.74 ± 22.03 MPa) exhibited a statistically significant increase in bond strength compared to the control group (54.87 ± 19.06 MPa) (p < 0.05). SEM analysis revealed a higher incidence of mixed failure patterns in the NSF-treated samples. However, the Chi-square test showed no significant difference in the distribution of fracture modes between the control and experimental groups, suggesting that NSF pre-treatment did not adversely affect the integrity of the dentin–adhesive interface. Although the findings underscore NSF’s potential as an anti-caries agent that enhances adhesive bond strength, the limitations of an in vitro study must be acknowledged, as such conditions do not fully replicate the complexities of the oral environment. Therefore, further research is warranted to explore the long-term effects of NSF application, including its impact on bond durability and material degradation under simulated clinical conditions.