*Editorial* **Future Prospective of Oral Microbiome Research**

**Yoshiaki Nomura 1,2,\*, Ayako Okada <sup>3</sup> and Nobuhiro Hanada <sup>2</sup>**


**Abstract:** Oral microbiome has complex structure. It consisted of more than 700 species of bacteria. These bacteria contains pathogens for human health. In contrast, some beneficial bacteria were included. Perspective of oral microbiome is not still elucidated. In this paper, information regarding oral microbiome of health older adults and oral diseases are included. Additionally, concise review of oral microbiome are presented.

**Keywords:** oral microbiome; next generation sequence; clinical application

An oral microbiome consists of more than 700 species of bacteria [1] and plays an important role in human health. In the past, disease-specific bacteria were focused on, many in vitro studies showed their pathogenesis, and their clinical examination system has developed. However, these disease-specific bacteria configure small, tiny fractions of oral microbiomes. The advance of next-generation sequencing and bioinformatics enabled us to study the proportion of each species in samples [2]. Despite this, there is still no clear definition of a healthy oral microbiome. The disturbance of a healthy oral microbiome, which is called dysbiosis, immensely contributes to human health. Therefore, there is a need to accumulate the data on the oral microbiome for every age category in humans, in addition to the disease stage.

In this article, the key species proposed in this paper are summarized in Table 1. Many of these species are relatively unfamiliar as the etiology of dental caries, periodontal disease, or other oral diseases. The pathogen of black stain is almost unknown. This study may give us the candidate for the pathogens of black stain for future research [3]. Periodontal pathogens in patients with Down syndrome were suggested to be different from chronic marginal periodontitis [4]. Molar–incisor malformation is a very rare disease, and the case report by [5] may contain valuable information regarding this. In general, *Firmicutes* is a predominant phylum, and *Streptococcus* is a predominant genius. These bacteria are supposed to be beneficial bacteria for human health. Some of them had been used as probiotic bacteria. However, some pathogenic species are predominant in healthy subjects. For example, predominant bacteria such as the *S. sinensis* group and *S. pneumoniae* group are known to be the pathogens for pneumonia [6,7].

In addition to this clinical evidence, this paper introduces the effect of biofilm composition on an experimental animal model for the development of dental caries [8] and reviews the effect of silver diamine fluoride on biofilm composition [9].

As the cost of next generation sequencing is high for the sample size study, the experiments presented in this paper were carried out by a small sample size study. Therefore, there is a need to accumulate the data of oral microbiome. The clinical application of the microbiome and its future prospects are reviewed [10]. Moreover, we hope that this paper may help guide future studies.

**Citation:** Nomura, Y.; Okada, A.; Hanada, N. Future Prospective of Oral Microbiome Research. *Appl. Sci.* **2022**, *12*, 55. https://doi.org/ 10.3390/app12010055

Received: 16 December 2021 Accepted: 21 December 2021 Published: 22 December 2021

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**Table 1.** List of the key species proposed in this paper.


**Table 1.** *Cont.*

**Author Contributions:** Conceptualization, Y.N., A.O. and N.H.; writing—original draft preparation, Y.N.; writing—review and editing, A.O. and N.H. All authors have read and agreed to the published version of the manuscript.

**Funding:** This study was supported by the JSPS KAKENHI (grant numbers 17K12030 and 20K10303) and the SECOM Science and Technology Foundation. The funders played no role in the design of the study, in data collection, in the analysis and interpretation of the results, or in the writing of the manuscript.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.

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