Metagenomic analysis of oral and intestinal microbiome of patients during the initial stage of orthodontic treatment.

INTRODUCTION: This prospective study analyzed changes in the oral and intestinal microbiomes in patients before and after fixed orthodontic treatment, elucidating the impacts of fixed orthodontic treatment on patient health and metabolism. METHODS: Metagenomic analysis was conducted on stool, dental plaque, and saliva samples from 10 fixed orthodontic patients. All the samples were sequenced with Illumina NovaSeq 6000 with a paired-end sequencing length of 150 bp. Identification of taxa in metagenomes and functional annotation of genes of the microbiota were performed using the data after quality control. Clinical periodontal parameters, including the gingiva index, plaque index, and pocket probing depth, were examined at each time point in triplicates. Patients also received a table to record their oral hygiene habits of brushing, flossing, and dessert consumption frequency over 1 month. RESULTS: The brushing and flossing times per day of patients were significantly increased after treatment compared with baseline. The number of times a patient ate dessert daily was also fewer after treatment than at baseline. In addition, the plaque index decreased significantly, whereas the pH value of saliva, gingiva index, and pocket probing depth did not change. No significant differences were observed between the participants before and after orthodontic treatment regarding alpha-diversity analysis of the gut, dental plaque, or saliva microbiota. However, on closer analysis, periodontal disease-associated bacteria levels in the oral cavity remain elevated. Alterations in gut microbiota were also observed after orthodontic treatment. CONCLUSIONS: The richness and diversity of the microbiome did not change significantly during the initial stage of fixed orthodontic treatment. However, the levels of periodontal disease-associated bacteria increased.