| Plaque biofilms, a well-organized microbial community on dental surface, is a major etiological factor of caries. Compared with planktonic bacteria, the bacteria in biofilms have the different gene expression and phenotype, as well as have an increased resistance to antimicrobials. In normal conditions, the microbial ecology of plaque biofilms is in a state of equilibrium, and the bacteria components of biofilms remain relatively stable. If the intake of suger is too frequent, the biofilms will be in a low pH in most of time, which will benefit the proliferation of S.mutans and Lactobacillus, and further lead to caries. So the control on the formation of plaque biofilms and the maintenance of microcosm homeostasis play an important role in preventing caries. Gallnut contains tannin abundantly and can be used as an effective drug in the prevention of caries. The aim of the our research was to investigate the effects of gallnut water extract on the plaque biofilms in vitro, thereby to explore its mechanism of preventing caries.1. The role of of gallnut water extract in eradicating plaque biofilmsIn this part, the minimal inhibitory concentrations(MIC) of all experimental strains were determined, and the role of gallnut water extract in eradicating plaque was further investigated by using the artificial mouth and the technology of colony counting. The resultsshowed that gallnut water extract could inhibit the growth of S.mutans, A.viscosus, S.sanguis and S.oralis. The MIC of S.mutans was 64mg/ml, which was same as A.viscosus and S.sanguis. The MIC of S.oralis was 8mg/ml; The plaque biofilms formed by S.mutans, A.viscosus, S.sanguis and S.oralis could be eradicated effectively by different concentrations of gallnut water extract respectively. With the increasing concentration, the number of bacteria was reduced gradually, and the effect was dose-dependent. Compared with the experiment in determining the MIC, it was found that even though higher concentration than MIC of gallnut water extract was adopted, the plaque biofilms couldn't be eradicated completely. It suggested that the eradication of plaque biofilms need a higher concentration of gallnut water extract comparing with the planktonics, which might correlate with the propert of plaque biofilms.2. The effects of gallnut water extract on the formation of plaque biofilmsThe artificial mouth, the technology of colony counting and scanning electron microscope(SEM) were used to investigate the effects of gallnut water extract on the formation of plaque biofilms. The results of colony counting showed that the amount of bacteria on enamel fragments treated with gallnut water extract was less than that of control team, and the difference between two groups was significant. The observation with SEM revealed that enamel fragments treated with gallnut water extract had no biofilm formed, the bacteria were distributed scatteredly, while the mature biofilm occurred on the control enamel fragments . So we can draw a conclusion that Chinese nutgall can inhibit the formation of oralbiofilm significantly.3. The effects of gallnut water extract on the composition of plaque biofilmsThe artificial mouth and the technology of selective culture ofbacteria were used to observe the effects of gallnut water extract on the composition of plaque biofilms. The results showed that gallnut water extract could reduce the proportion of S.mutans and A.vicosus, and increase the proportion of S.sanguis and S.oralis, It suggested that gallnut water extract can prevent the selective growth of S.mutans in biofilms, and can reduce the harmful conversion of microbial.4. The effects of gallnut water extract on the vitality of plaque biofilms model in the oral cavityThe technology of EB/FDA staining and CLSM were used to observe the effects of gallnut water extract on the vitality of of plaque biofilms on the basis of establishing a plaque biofilms model in the oral cavity. The results showed that gallnut water extract could decrease the vatility of plaque b...
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