| Adhesive dentistry has been the focus of dental research. Resin-based materials were reported to accumulate more dental biofilm than other restorative materials. Since the bonding have no antibacterial activities, bacteria could get through the gap between adhesive resin and tooth structure, leading to the bonding failure. Therefoe, resin-based materials with antibacterial activities should be developed to solve this problem.Recently, our research group synthesized several antibacterial polymer monomers, and DMAE-CB is the best one.However, there is one aliphatic C=C in the molecular structures of DMAE-CB. When copolymerization reaction occurred, the degrees of monomer conversion were low. Only a small amount of antibacterial monomer could polymerize with resin monomer matrix, and therefore the antibacterial activities of dental materials incorporating DMAE-CB monomer were limited, and the unpolymerized monomers would exert unwanted side-effects against surrounding tissues. Therefore, two new experimental quaternary ammonium modified monomers MAE-DB and MAE-HB were developed. There are two polymerizable aliphatic C=C in the molecular structures of them. When copolymerization reaction occurs, the degrees of monomer conversion of MAE-DB and MAE-HB monomers will be higher than that of DMAE-CB monomer. More antibacterial monomers could polymerize with resin matrix, and the release of antibacterial agents into the surrounding tissues can be reduced.1 The main objectives:In this study, the antibacterial activities and cytotoxicities of MAE-DB and MAE-HB monomers will be tested. Then the properties of Single bond 2 incorporated with MAE-DB and MAE-HB monomers and experimental composite resins incorporated with MAE-DB and MAE-HB monomers will be evaluated.2 The main methods:2.1 The antibacterial activities of MAE-DB and MAE-HB monomers were evaluated by MIC/MBC tests, and the time–kill determinations were performed to test the killing kinetics of them.2.2 The bacterial morphologies were observed using Fe-SEM and CLSM.2.3 MTT method was used to evaluate the cytotoxicities of MAE-DB and MAE-HB monomers.2.4 The effect of the cured Single Bond 2 incorporated with MAE-DB and MAE-HB monomers and experimental composite resins incorporated with MAE-DB and MAE-HB monomers were evaluated by film contact test.2.5 The mechanical properties and curing abilities of experimental composite resins incorporated with MAE-DB and MAE-HB monomers were evaluated by hardness test.2.6 The relative level of gtfB gene expression by S.mutans contact with experimental composite resins incorporated with MAE-DB and MAE-HB monomers were quantified using real-time RT-PCR.3 The main results:3.1 There was no difference among the MIC values of MAE-DB, MAE-HB, DMAE-CB and Chlorhexidine acetate. Higher concentrations of MAE-DB and MAE-HB could lead to a rapid decrease in bacterial numbers and could disturb the integrity of bacteria.3.2 The cytotoxicities of MAE-DB and MAE-HB were lower than that of Bis-GMA.3.3 The antibacterial activities of cured Single Bond 2 incorporated with MAE-DB and MAE-HB monomers were increased with the incorporated concentration increased. No differences were found between the antibacterial activities before and after aging for 180d. The antibacterial activities of 4%MAE-DB,7%MAE-DB,10%MAE-DB,4%MAE-HB,7%MAE-HB and 10% MAE-HB groups were better than that of 3%DMAE-CB group.3.4 It can be seen from the SEM micrographs that the bacteria generated on the surface of 3%DMAE-CB, 1%MAE-DB, 4%MAE-DB, 1%MAE-HB and 4%MAE-HB Single bond 2 groups were fewer than that of control group. The numbers of bacteria generated on the surface of 7%MAE-DB, 10%MAE-DB, 7%MAE-HB and 10%MAE-HB Single bond 2 groups were very little.3.5 The CLSM images demonstrated that for 1%MAE-DB, 4%MAE-DB, 1% MAE-HB, 4%MAE-HB and 3%DMAE-CB Single bond 2 groups, the ratio of bacteria with abnormal strctures and bacteria with normal strctures were not very high. However, for 7%MAE-DB, 10%MAE-DB, 7%MAE-HB and 10%MAE-HB Single bond 2 groups, the ratio of bacteria with abnormal strctures and bacteria with normal strctures were very high.3.6 The bonding strengths of Single Bond 2 incorporated with MAE-DB and MAE-HB monomers were lower than that of control group. Differences were found among 10%MAE-DB, 10%MAE-HB Single Bond 2 groups and control group and 3%DMAE-CB Single Bond 2 group. For 10%MAE-DB and 10%MAE-HB Single Bond 2 groups, the hybrid layers were intact, a few of short resin tags could be observed. The main fracture modes of 10%MAE-DB and 10%MAE-HB Single Bond 2 groups were fracture in the adhesive interface.The main fracture modes of all the other groups were mixed failures.3.7 The bonding strengths of Single Bond 2 incorporated with MAE-DB and MAE-HB monomers after 1,0000 thermocycling were lower than that before thermocycling. Differences were found among 10%MAE-DB, 10%MAE-HB Single Bond 2 groups and the control group and 3%DMAE-CB Single Bond 2 group. Cracks could be founded in the hybrid layer of 10%MAE-DB and 10%MAE-HB Single Bond 2 groups. The numbers of resin tags were decreased and fractured resin tags could be observed. The main fracture modes of 10%MAE-DB and 10%MAE-HB Single Bond 2 groups were fracture in the adhesive interface. The main fracture mode of all the other groups was mixed failure.3.8 After 1,0000 thermocycling, microleakages occurred in all the groups, the extent of microleakages of 10%MAE-DB and 10%MAE-HB Single Bond 2 groups were severe.3.9 The mean value of cell viability of the control group was 93%. The mean values of cell viability of the 10%MAE-DB, 10%MAE-HB and 3%DMAE-CB groups were 60%-70%. The mean values of cell viability of the rest groups were 80%-90%.3.10 The antibacterial activities of cured experimental composite resins incorporated with MAE-DB and MAE-HB monomers were increased with the incorporated concentration increased. 10%MAE-DB and 10%MAE-HB groups were better than that of the other groups. No differences were found between the antibacterial activities before and after aging for 180d.3.11 It can be seen from the SEM micrographs that the bacteria generated on the surface of 3%DMAE-CB, 1%MAE-DB, 4%MAE-DB, 1%MAE-HB and 4%MAE-HB experimental composite resins were fewer than that of control group. The numbers of bacteria generated on the surface of 7%MAE-DB, 10%MAE-DB, 7%MAE-HB and 10%MAE-HB experimental composite resins were very little.3.12 Differences were found between the hardnesses of 7%MAE-DB, 7%MAE-HB,10%MAE-DB,10%MAE-HB experimental composite resins and that of the control group.The hardnesses of 10%MAE-DB and 10%MAE-HB were the highest in all the groups.3.13 The mean value of cell viability of 3%DMAE-CB experimental composite resin was 70%. The mean values of cell viability of the rest groups ranged from 80%-90%.3.14 Differences were found between the gtfB gene expression of 10% MAE-DB, 10%MAE-HB experimental composite resins and that of the control group.4. The main conclusions:4.1 The antibacterial activities of MAE-DB and MAE-HB monomers were the same as that of DMAE-CB monomer, and could lead to a rapid decrease in bacterial numbers, and disturb the integrity of bacteria and cause lysis of the bacterial cells.4.2 The cytotoxicities of MAE-DB and MAE-HB monomers were lower than that of Bis-GMA.4.3 The antibacterial activities of cured Single Bond 2 incorporated with MAE-DB and MAE-HB monomers were increased with the incorporated concentration increased. No differences were found between the antibacterial activities before and after aging.4.4 The bonding strengths of 10%MAE-DB and 10%MAE-HB Single Bond 2 groups were lower than that of the control group. The extent of microleakages of 10%MAE-DB and 10%MAE-HB Single Bond 2 groups were severe.4.5 The cytotoxicities of 10%MAE-DB, 10%MAE-HB and 3%DMAE-CB Single Bond 2 groups couldn't meet the requirements of clinical use.4.6 The antibacterial activities of cured experimental composite resins incorporated with MAE-DB and MAE-HB monomers were increased with the incorporated concentration increased. 10%MAE-DB and 10%MAE-HB groups were better than that of the other groups. No differences were found between the antibacterial activities before and after aging.4.7 No differences were found among all groups in the mechanism propoties and curing abilities of the experimental composite resins incorporating the MAE-DB and MAE-HB monomers. 4.8 The cytotoxicities of experimental composite resins incorporated with MAE-DB and MAE-HB monomers could meet the requirements of clinical use.4.9 MAE-DB and MAE-HB monomers could inhibit the gtfB gene expression of S. mutans.Conclusively, the newly developed polymerizable QAS monomers, MAE- DB and MAE-HB, exhibited strong bactericidal activities against eight strains of oral bacteria. 7% was the most suitable concentration of Single Bond 2 incorporated with MAE-DB and MAE-HB monomers. And 10% was the most suitable concentration of experimental composite resin incorporated with MAE-DB and MAE-HB monomers. The results indicated that MAE-DB and MAE-HB, which have two polymerizable aliphatic C=C in the molecular structures, were better than DMAE-CB monomer, which have only one polymerizable aliphatic C=C. MAE-DB and MAE-HB might be good candidates for antibacterial monomers for improving the antibacterial activity of dental materials.
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