16S ribosomal RNA (rRNA) genetic analysis
Amplicons were adjusted for 16S RNA genetic analysis according to the manufacturer's protocol (16S Ribosomal RNA Gene Amplicons for the Illumina MiSeq System guidelines, Illumina, 2020). The V3–V4 region of the 16S rRNA gene of the extracted DNA was amplified using KAPA HiFi Hot Start Ready Mix (Roche) with the primer pair 341F (5′‐TCGTCGGCAGCGTCAGATGTGTATAAGAGACAGCCTACGGGNGGCWGCAG‐3′) and 806R primer (5′‐GTCTCGTGGGCTCGGAGATGTGTATAAGAGACAGGACTACHVGGGTATCTAATCC‐3′). Sequencing was performed for 600 cycles using Nextera XT Index Kit V2 (Illumina) as an adapter and the Miseq Reagent Kit v3 (Illumina) for pair ends. The FASTQ file obtained by Miseq measurement was analyzed using QIIME2 (2019.7), an integration analysis pipeline. Low‐quality sequence reads were filtered using the DADA2 package. The sequence errors and chimera sequences were filtered to estimate amplicon sequence variants (ASVs). The obtained ASVs were collated with the Human Oral Microbiome Database to assign bacterial species. The obtained sequence data have been deposited in DDBJ (DDBJ accession number: DRR385398–DRR385749).