SRP213699 PRJNA552608 Alterations of subgingival microbiota during full-fixed appliance orthodontic treatment – a prospective study Full-fixed appliance orthodontic treatment (commonly called braces) increases plaque accumulation and risk of periodontal disease. However, little consensus exists on changes of subgingival microbiota and specific periodontopathogens during orthodontic treatment. Prior studies have been hampered by selection biases due to culturing methods and candidate-based PCR methods. Considering the enormity of the oral microbiome and the limitations of prior studies, we performed 16S rRNA next-generation sequencing (NGS) of 168 subgingival samples and demonstrate that a niche specific microbiome (buccal sites vs lingual site) in subgingival microbiomes exist in all participants before orthodontic treatment; Lingual site harbors significant higher diversity of the microbiome than buccal site. We identified a number of specific novel microbial species that were enriched during orthodontic treatment. Interestingly, distinction of the microbiome between buccal site and lingual site is diminished after orthodontic treatment. Collectively, we have generated for the first time, global profiles of subgingival microbiomes during early stages of full-fixed appliance orthodontic treatment.