Abstract: Objective: To explore the formation and maintenance mechanism of microorganisms in human oral cavity. Methods: Oral flora of 20 patients with oral health and disease were investigated, and the abundance of five common bacteria genera-Granulicatella, Porphyromonas, Corynebacterium, Leptotrichia, and Tannerella were analyzed. Results: Bacteria in the healthy mouth presented significant asynchronous fluctuation trend, while the fluctuation of bacteria in the mouth with disease is a stationary random process. The two basic response delays in the healthy mouth, i.e. reproductive delay and reaction delay, were identified, which were accompanied with interspecific delay and substrate decomposing delay. These delayed responses could cause asynchronous periodic fluctuations of the number of each species and thus form and maintain high species diversity. Based on the experimental data and hypothesis, an effective dynamic model of oral flora succession system was established. Conclusion: The effectiveness of the proposed oral microbiome succession mechanism was confirmed by a large number of simulation experiments.

Key words: oral microbial diversity, delay responses, system dynamic model, digital simulation