| Summary: | Background Clear aligners are well known for facilitating oral hygiene maintenance and decreasing susceptibility to periodontal diseases as compared to conventional fixed appliances. However, few research studies focus on the subgingival microbial community during clear aligner treatment (CAT). Hence, this study investigates changes of the subgingival microbial community and its association with clinical characteristics during the first three months of CAT. Methods Ten female patients with clear aligners were enrolled in this study. Subgingival plaque samples were obtained at three time points: before orthodontic treatment (T0), one month after orthodontic treatment (T1) and three months after orthodontic treatment (T2). DNA was then extracted from plaque samples and analyzed by 16S rRNA gene sequencing. Periodontal examinations, including plaque index (PI) and gingival bleeding index (GBI) measurements were also recorded. Results The plaque indices (PIs) and gingival bleeding indices (GBIs) were slightly increased at T1 and T2, but no statistically significant difference was found. The alpha diversity indices, including the ACE, Chao1, Shannon indices, all showed a declining trend without significance, and a rising trend in the Simpson diversity index was observed. The weighted UniFrac distance was significantly higher at T1 and T2 compared with T0. Principal Coordinates Analysis (PCoA) demonstrated that the communities at T0 tended to cluster apart from the communities at T1 and T2. The relative abundance of the phylum Firmicutes and genus Mycoplasma was significantly increased at T0 compared with T2. There was no significant difference in the relative abundance of periodontal pathogens at the genus and species levels or core microorganisms at the genus level. Conclusion A slightly decreasing microbial diversity with a significant change of microbial structure was found during the first three-month clear aligner treatment (CAT). However, subjects receiving clear aligner treatment were free from periodontal diseases with relatively stable levels of periodontal microorganisms and core microorganisms. Thus, our preliminary findings indicated that clear aligners induced nonpathogenic changes of the subgingival microbiome in the first three-month treatment.
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