Dysbiosis of oral microbiome persists after dental treatment-induced remission of periodontal disease and dental caries
Authors: Yama Kazuma , Nishimoto Yuichiro , Kumagai Kota , Jo Ryutaro , Harada Minori , Maruyama Yuki , Aita Yuto , Fujii Narumi , Inokuchi Takuya , Kawamata Ryosuke , Sako Misato , Ichiba Yuko , Tsutsumi Kota , Kimura Mitsuo , Murakami Shinnosuke , Kakizawa Yasushi , Kumagai Takashi , Yamada Takuji , Fukuda Shinji 
Published: September 2023

ABSTRACT
Oral diseases, such as periodontal disease and dental caries, have a high risk of recurrence and are considered to be related to dysbiosis of the oral microbiome and metabolome. It is, therefore, important to understand the state of the oral microbiome and metabolome after disease treatment to prevent recurrence. The current study sought to clarify whether oral dysbiosis improves the following remission of symptoms by dental treatment. To this end, the salivary microbiome and metabolome of healthy participants were compared to those with periodontal disease, dental caries, or both (concurrent). Saliva was collected as mouth-rinsed water and the microbiome was measured using 16S rRNA gene targeted sequencing and metabolome using capillary electrophoresis–time-of-flight mass spectrometry. Comparisons with healthy participants were performed before and after treatment, and several months after transition to self-care. Dental treatment significantly improved the oral health condition of each group; several months after treatment, oral health did not deteriorate. However, even after remission, the salivary microbiome of the two groups (oral disease and healthy) differed significantly. Additionally, after remission, significant differences, compared with healthy participants, remained in the relative abundances of disease-related bacteria and nitrate-reducing bacteria. After remission, significant differences were observed in the salivary metabolome in the healthy group in terms of threonate and pyrimidine metabolism-related component concentrations, which are assumed to reflect the high relative abundance of periodontal disease-related bacteria in the microbiome. Oral microbiome dysbiosis persisted even after dental treatment-induced disease remission with a sustained increased risk of disease when compared with healthy participants.

IMPORTANCE
We characterized the oral conditions, salivary microbiome, and metabolome after dental treatment by investigating the state after treatment completion and transition to self-care. Dental treatment improved oral health conditions, resulting in oral disease remission; however, the imbalanced state of the salivary microbiome continued even after remission. Although the results of this study are preliminary, owing to the small number of participants in each group when compared to larger cohort studies, they indicate that the risk of disease may remain higher than that of healthy participants, thereby demonstrating the importance of removing dental plaque containing disease-related bacteria using appropriate care even after treatment completion. We also identified bacterial species with relative abundances that differed from those of healthy participants even after remission of symptoms, which may indicate that the maturation of certain bacterial species must be controlled to improve the oral microbiome and reduce the risk of disease recurrence.