# Core Microbiota Promotes the Development of Dental Caries
## 4 Discussion  
Dental caries including ECC, is a multifactorial disease [37,38]. Microbes are considered as one of the main pathogenic factors of ECC. A large amount of evidence proves that there might be a core microbiome of diseases in the oral cavity [39,40]. This also partially explains why some people are susceptible to caries while others are not. However, most of the literature have inferred the existence of core microbiome by sequencing and have found that tremendous species and genera were related to caries but failed to construct models to verify the casual relationship between dental caries and the core microbiota. A longitudinal study further narrowed the core microbiome and demonstrated that the core microbiota played an important role in ECC [13]. Referring to this literature, for the first time, we developed a core microbiota biofilm model containing four representative bacteria of ECC during its occurrence and development, which proved to promote the progress of dental caries both in vitro and in vivo. Many studies have also shown that the four microorganisms we selected including _V. parvula, F. nucleatum, P. denticola,_ and _L. wadei_ are closely related to caries, especially ECC. In our study, we found that after 24 h, 48 h, and 72 h of culture, _V. parvula_ accounted for more than half of the core microbial biofilm. Similarly, a large number of studies have proven that _Veillonella_ content in ECC is higher than that in non-caries children, suggesting that it is closely related to ECC [13,41,42,43,44, 41]. In another study, _Fusobacterium_ was found to be significantly higher in ECC [45], in which _F. nucleatum_ is closely associated with ECC, especially severe ECC [43,46]. Our study found that the amount of _F. nucleatum_ in the biofilm at 72 h was about twice that at 24 h in the Core + _S. mutans_ biofilm, which also seems to suggest that _F. nucleatum_ is more related to severe ECC. Meanwhile, with the extension of the Core + _S. mutans_ biofilm culture time, the content of _P. denticola_ also increased. _P. denticola_ was found to be one of the most prevalent species in the S-ECC, shown to be associated with dental caries. There is also speculation that the proportion of _P. denticola_ would reduce after comprehensive restorative and preventive dental treatment [47,48]. Our results showed that when _S. mutans_ was added, the content of _L. wadei_ increased at the early stage of biofilm formation, which implied that _S. mutans_ might promote the growth of _L. wadei. L. wadei_ was found to be overrepresented in caries-active dental plaque compared to caries-free [49]. Moreover, a large number of _Fusobacterium_, _Prerotella_, and _Leptotrichia_ were observed in a group of children with active caries [13,43,50]. In summary, these previous studies proved the rationality of our choice of four strains as core microbiota. We found that the core microbiota had the effects of promoting the growth of _S. mutans_. There have been some controversies about the effect of _V. parvula_ on _S. mutans_. Some  
Figure 4: In vivo carigenesis ability of different biofilms. (**a**) Representative hemisectioned molars in each group under stereoscopic microscopy. (**b**) Caries score by [PERSON] method (n = 5). E = Enamel caries; Ds = slight dental caries; Dm = moderate dental caries; Dx = extensive dental caries. The severity decreased in the order of Core + _S. mutans_, _S. mutans_, Core and control groups. * \(p\) < 0.05; **_p_ < 0.01; *** \(p\) < 0.001.  
previous studies have shown that _V. parvula_ might contribute to acid production and the growth of _S. mutans_[43; 51; 52]. However, it has also been found that _V. parvula_ had little effect on the _S. mutans_ growth when co-cultured with _S. mutans_ and _Streptococcus gordonii_ compared with _S. mutans_ alone [53]. There might be a certain relationship between _V. parvula_ and _S. mutans_, but the impact of _V. parvula_ in the Core microbiota on _S. mutans_ remains to be studied. Similarly, _F.