Evaluation of nisin-added adhesive resins: antimicrobial properties, dentin bond strength, degree of monomer conversion and structural/chemical characterization.

This study evaluated the antibacterial effect, dentin bond strength, monomer conversion degree, and chemical structure of an adhesive resin containing nisin, an antimicrobial peptide (AMP) derived from Lactococcus lactis. Antimicrobial activity against S. mutans was tested using a disk diffusion method with various nisin concentrations (1:1 to 1:80). The optimum concentration, 1:40, was selected for further testing. The adhesive was characterized using XRD, EDX, FT-IR, and SEM analyses. For bond strength testing, 80 caries-free molars with enamel removed were divided into control and AMP groups, each further subdivided into etch-and-rinse or self-etch application subgroups (n = 20). FT-IR was used to measure monomer conversion degrees, and data were statistically analyzed. Antimicrobial testing showed inhibition zones of 27 mm for nisin alone, 9 mm for resin, and 12 mm for resin with 1:40 nisin. SEM and EDX analyses confirmed homogeneous nisin distribution, while XRD indicated no structural changes to the adhesive. In the etch-and-rinse mode, the AMP group exhibited higher bond strength compared to the Control group though the difference was not statistically significant (p > 0.5). Similarly, no significant differences were observed between the groups in the self-etch mode (p > 0.5). When comparing the bond strengths of adhesive resins according to the application protocol, no significant differences were found between the etch-and-rinse and self-etch modes for either adhesive (p > 0.5). The experimental adhesive exhibited a lower monomer conversion degree than the control group (p < 0.05). The nisin-containing experimental adhesive showed antimicrobial activity against S. mutans, preserved bond strength in etch-and-rinse and self-etch mode, and maintained its structural integrity.