The study aimed to investigate the antibacterial and antiproteolytic effects of chlorhexidine (CHX) in adhesive procedures, assessing its impact at baseline, after biological loading, and after 6- or 12-month storage in distilled water or artificial saliva. It comprised two parts: biological loading of restorations in a bacterial caries model involving 60 teeth and microtensile bond strength (μTBS) testing on 2979 sticks. Groups included a control with a 3-step adhesive, 2% CHX as dentine pre-treatment, 0.1% CHX in primer, 0.1% CHX in bonding, and a 2-step adhesive with 0.2% CHX. Class V composite restorations were subjected to a 10-day caries model with S. mutans, and demineralization was evaluated using fluorescence microscopy and SEM for marginal analysis. μTBS was tested at various intervals, with fracture mode analysis performed. Results indicated that while none of the CHX adhesives prevented secondary caries formation, the 2% CHX dentine pre-treatment effectively limited marginal gap formation in enamel. Bond strength of CHX adhesives was inferior to the control at baseline and significantly decreased after the caries model. Notably, only the primer with 0.1% CHX maintained μTBS values after 12 months in saliva, suggesting a potential antiproteolytic effect.
