[Establishment and evaluation of the in vitro dynamic biofilm model]

To establish a dynamic model which could simulate the ecologic environment of oral cavity and study the cariogenicity of oral biofilm, continuously observe the formation of oral biofilm.

The fermental vessel and chemostat were designed according to the purpose of the study. Four strains of oral bacteria, namely Streptococcus mutans, Streptococcus sanguis, Lactobacillus rhamnosus and Actinomyces naeslundii, were inoculated in the fermenter. The hydroxyapatite (HA) discs and glass slides were put in the chemostat. The temperature, oxide pressure, pH, dilution rate, circulation rate and substrate of the chemostat were carefully modulated. Distilled water and 25mM sucrose solution were used to test the stability of the system. At the beginning of the model establishment, the anabiosis bacteria were inoculated in fermenter full of fresh artificial saliva with a dilution rate of 10%. After the growth of bacteria in the fermenter was stable, the four-organism bacterial consortium was inoculated in the chemotat for 24 hours together with fresh artificial saliva (v/v=1:9). The organisms in planktonic phase were examined everyday. When the populations of consortium got stable(about 72 hours), the test solution was pulsed in the chemostat every 12 hours for 5 days. The HA discs and glass slides were observed every 24 hours for five times. The data was analyzed using SPSS 10.0 software package. Dunnet t test was used to compare the difference between the two groups at the level of alpha=0.05.

The dynamic model was successfully established on oral biofilm study. With the pulse of sucrose solution, the environment in the chemostat simulated the cariogenic environment in nature, and all data namely the bacteria population, the biofilm microstructure changed with solution pulse. CONCLSUIONS: The model established is proved to be stable and the parameters in the model could be successfully controlled. The model fulfills the dynamic observation of formation of biofilm and caries lesion in vitro.