Bioactive universal adhesive containing polyhexamethylene biguanide: Antimicrobial and mechanical properties and bonding to sound dentin

To evaluate the effect of incorporating different concentrations of polyhexamethylene biguanide (PHMB) into a universal adhesive on its antimicrobial activity, mechanical properties, and adhesion to sound dentin. Five adhesive formulations containing PHMB at concentrations of 0% (control), 0.05%, 0.1%, 0.5% and 1% (wt %) were evaluated. Antimicrobial activity was assessed using the inhibition zone against S. mutans. Mechanical properties were evaluated through Vickers microhardness (VHN) and ultimate bond strength (UTS), measured both immediately and after 28 days of water storage at 37 °C. Bonding performance was assessed in resin-dentin bonded bars prepared using either an etch-and-rinse or self-etch strategy. Microtensile bond strength (μTBS) and nanoleakage (NL) were evaluated immediately (IT) and after thermocycling (AT) (10.000 cycles; 5 °C/55 °C). Additionally, the degree of conversion (DC) at the adhesive interface was assessed using micro-Raman spectroscopy. Data were analyzed using ANOVA followed by Tukey's test (α = 0.05). PHMB-containing adhesives produced significantly larger inhibition zones against S. mutans compared with the control (p < 0.001). Higher PHMB concentrations (≥0.5%) resulted in significantly reduced VHN, UTS and μTBS values (p < 0.01). No significant differences in DC were observed between the control. 0.05, and 0.1% PHMB groups (p > 0.05). The findings suggest that incorporating 0.05% PHMB into a universal adhesive can provide effective antimicrobial activity without compromising its mechanical properties or adhesion to sound dentin. • The addition of PHMB to a universal adhesive provides an antimicrobial effect. • Low concentrations of PHMB (0.05%) do not compromise the mechanical or bonding properties. • PHMB concentrations above 0.1% into a universal adhesive induce structural weakening of the polymer network.