| With regard to commonly used dental resin materials have no antibacterial effect after being-cured, which may explain why composites accumulate more plaque to cause a secondary caries happen. Providing composites with antibacterial properties is a long-term goal of the oral science. Quaternary ammonium salt is as a cationic active biocide with high efficiency spectrum, low toxicity, chemically stable performance, long-lasting biological activity. The dental resin is with long-lasting, stable antibacterial properties when quaternary ammonium antibacterial agents were immobilized in the rein matrix, which play a preventive role of secondary caries.Five new liquid quaternary ammonium salts (MEBH-TMEDMA-MEBH, MEBH-DMO, MEBH-DBA, MEBU-DMO, MEBU-DBA) were synthesized according to the characteristic of solid-phase contact antibacterial mechanism, which are characterized by infrared spectroscopy (IR), nuclear magnetic resonance ('H-NMR) and liquid chromatography-mass spectrometer (LC-MS) to determine the structure and purity.These five quaternary ammonium salts were compounds of the antibacterial agent quaternary ammonium and methacryloyl group, and the antibacterial agent is covalently bound to polymer matrix by copolymerization with other monomers when the material is cured. The influence of the types and the amount of monomers on degree of conversion was investigated using FT-IR spectrophotometry, the result showed that quaternary ammonium salts promotes polymerization. The chemical composition of the surface of resin that is with different concentration of antibacterial monomer was characterized by using X-ray photoelectron spectroscopy(XPS), the result showed that N+ content increases with the increasing of addition of monomer concentration. Hydrophilic of composites incorporating quaternary ammonium salt became better than the control, which may prevent bacterial adhesion on the surface. While composites were soaked in the artificial saliva 3h, whose surface contact angle decreased, and that incorporating MEBH-TMEDMA-MEBH monomer dropped 9°. The thermal stability of the dental resin was detected by TG and DMTA. The result showed that the resin containing quaternary ammonium salt have some advantages such as better thermal stability, greater rigidity, more homogeneous network.The minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) of these five quaternary ammonium salts against staphylococcus aureus were tested using a broth dilution test. The MEBU-DBA showed strong antibacterial activity and its MIC value was 12μg/mL. The inhibitory effect of composites incorporating quaternary ammonium salt against the growth of Streptococcus mutans on its surface was determined by counting the number of viable cells. The result showed that the antibacterial activities of cured experimental composite resins incorporated with antibacterial monomers were increased with the incorporated concentration increased and the structure of the carbon chain length and positive charge density of compounds affect antimicrobial activity. It can be seen from the SEM micrographs that the bacteria generated on the surface of experimental composite resins were fewer than that of control group. |
