| Second cares has become the primary reason for the replacement of dental restoration. Residue bacteria, plaque accumulation, microleakage and nanoleakage are all factors that may render restorations under the threat of caries-related bacteria and their metabolic products. Taking these factors into consideration, it is supposed that efforts can be made in the following aspect to protect against second caries. First, the surface of restorations should be smooth enough to hamper the adhesion and accumulation of plaque. Second, marginal leakage should be reduced to prevent the colonizing of bacteria at the restoration-dentin interface. Third, grand new functional restorative materials with preventative effects should be developed. Fourth, good health habits should be established and oral hygiene should be improved. Considering that the smoothness of restorative materials is largely determined by their own physical and mechanical properties, microleakage and nanoleakage are difficult to be eliminated and dental health education is greatly influenced by the cooperation of patients, we suppose that the development of new functional material may be the most effective strategy in the prevention of second-caries.Except glass inomer which may present some anti-caries effects due to the release of fluoride, the majority of modern restorative materials are not able to function against second-caries formation. Realizing that adhesive dentistry is now widely used in clinical practice, we are considering developing a bio-active bonding system with antibacterial property which can act as a cavity disinfectant before curing and act as an contact bacterial inhibitor after curing. This new adhesive system may hamper the formation of secondary-caries and hence lengthen the duration of adhesive restorations. Quaternary ammonium salt modified monomers are constructed by combining a polymerizable group with an antibacterial group. When quaternary ammonium monomer is incorporated in adhesive sqstems, the polymerizable group enables the monomer to be immobilized in the resin matrix while the antibacterial group inhibit bacterial growth upon contact.The purpose of this study was to choose the most active and less cytotoxic antibacterial monomer from the four monomers previously synthesized, incorporate it in a commercial adhesive system Single Bond 2, test the antibacterial property, bonding strength, color stability and cytotoxicity of the experimentl adhesive. The results of this study showed among the four ammonium monomer tested, DAME–CB exhibited strong and rapid antibacterial activity. The minimal bactericidal concentration(MBC) was between 2.4-9.8 ?g/ml, while at the concentration that is four time of MBC,, it was able to eliminate 99% of bacteria within 5-minutes'contact. When DMAE–CB was incorporated in Single bond 2, the experimental adhesive exhibited significant and stable antibacterial activity with no reduction on bonding strength and color stability. Finally, cytotoxicity test revealed that the two stronger antibacterial monomers DMAE-CB and DMAE-TB have some toxic effect on mouse fibrolast cell line L929. However, the cytotoxicity of the two monomers are comparable to that of some commonly used dental monomers, and when the antibacterial monomer is incorporated in Single Bond 2 at 3% The experimental adhesive showed no significant cytotoxocity effect after curing.In conclusion, the incorporation of ammonium monomer into Single Bond 2 to attempt a bio-active adhesive may be a promising strategy to prevent secondary-caries and worth further exploration.
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