Engineering a multifunctional dental adhesive via direct incorporation of a catechol-based monomer

To evaluate how direct incorporation of N-(3,4-dihydroxyphenethyl)methacrylamide (DMA), a mussel-inspired catechol monomer, affects the physicochemical, antibacterial, polymerization, and dentin-bonding properties of an experimental adhesive.

DMA was incorporated into a Bis-GMA/HEMA-based resin at 0.5, 1.0, or 1.5 wt%. Mechanical properties before and after 28-day water aging, water sorption (Wsp), water solubility (Wsl), DMA release, color stability, contact angle, Streptococcus mutans (S. mutans) biofilm formation, degree of conversion (DC), microtensile bond strength (μTBS), nanoleakage, failure modes, and cytotoxicity were evaluated. Bonding performance was assessed before and after 10,000 thermocycles, with Single Bond 2 (SB2) as a commercial reference.

DMA increased immediate flexural strength, elastic modulus, and nanohardness, but these advantages were not maintained after 28-day water aging, during which flexural strength and modulus of elasticity declined significantly in all groups. Wsp, Wsl, and contact angle were unaffected, whereas color change increased with DMA concentration. Only 7.9-10.8% of incorporated DMA was released over 28 days. DMA reduced S. mutans biofilm accumulation and increased bacterial death. The 1.5 wt% group showed a reduced DC after 20 s irradiation and exhibited > 50% premature specimen failure, and was therefore excluded from subsequent bonding tests. Immediate μTBS was unchanged by 0.5-1.0 wt% DMA. After thermocycling, μTBS and nanoleakage deteriorated significantly in the SB2 and Control but remained statistically stable in DMA-containing groups. Cell viability remained above approximately 70%.

Direct DMA incorporation conferred antibacterial activity and contributed to preservation of resin-dentin interfacial stability during aging, but higher loading compromised polymerization and color stability. A 0.5-1.0 wt% DMA range provided the most favorable overall balance for this experimental adhesive.