Introduction: Secondary caries at tooth-restoration margins caused by the formation of cariogenic biofilms has been considered the most common reason (40-70%) for restoration replacement, limiting the longevity of dental resin composite restorations and costing tens of billions of dollars annually. Resin composites experience biochemical breakdown in the oral cavity, catalyzed by salivary and bacteria derived enzymes, which may contribute to marginal breakdown. In this work, 5,5-dimethylhydantoin (5,5-DMH) was chemically modified to produce a light curable antimicrobial monomer. This monomer can be covalently attached to a methacrylate composite resin system during polymerization, creating a composite resin that could inhibit bacterial growth and adhesion over its surface for the life of the restoration (years), potentially reducing the rate of recurrent caries and increasing the service life. Materials and Methods: 5,5-DMH was activated by reaction with potassium hydroxide. Then, it was reacted with allyl bromide in methanol, producing the alkene modified product. After purification, the compound was halogenated by mixing with dilute chlorine bleach, followed by washing three times with water. The hydantoin derived antimicrobial monomer was added to the dental resin composite in the following ratios: 0%, 0.1 %, 0.5% and 1.0%, by weight. Preliminary work assessing the physical and mechanical properties of the cured resins has been conducted following photocuring (40 sec) the resin composites formulations. Gel content (n=3) was determined after 48 hours of incubation in acetone. Degree of conversion was tested using a Fourier Transform Infrared Spectroscopy (FT-IR) spectrophotometery after 24h. The advancing contact angles of water on the cured films (n=5) were determined using a contact angle goniometer. A three point bending test and compressive test were used to evaluate flexural strength and modulus of elasticity and compressive strength, respectively (n=5). Results: The final monomer was synthesized (yield=80%) and structure confirmed by Nuclear Magnetic Resonance (NMR) and FT-IR. The monomer was immobilized within the composite resin matrix without changing its physical and mechanical properties. Discussion and Conclusion: NMR and FT-IR confirmed the synthesis of the desired light curable antimicrobial monomer. The monomer incorporation to the composite resin matrix provided higher degree of cross-linking and conversion comparable with resins in the literature. The addition of antimicrobial monomer did not affect either the mechanical behavior or wettability of the dental resin composites. Future work will characterize biological behavior of the antimicrobial composite resins by the addition of the hydantoin monomer synthesized to the dental resin composite system as well as the antibacterial performance against several microorganisms, as individual challenges, or as part of a polymicrobial biofilm.
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