ABSTRACTThe purposes of this study were to examine the compositional changes in the salivary microbiota according to the severity of periodontal disease and to verify whether the distribution of specific bacterial species in saliva can distinguish the severity of disease. Saliva samples were collected from 8 periodontally healthy controls, 16 patients with gingivitis, 19 patients with moderate periodontitis, and 29 patients with severe periodontitis. The V3 and V4 regions of the 16S rRNA gene in the samples were sequenced, and the levels of 9 bacterial species showing significant differences among the groups by sequencing analysis were identified using quantitative real-time PCR (qPCR). The predictive performance of each bacterial species in distinguishing the severity of disease was evaluated using a receiver operating characteristic curve. Twenty-nine species, includingPorphyromonas gingivalis, increased as the severity of disease increased, whereas 6 species, includingRothia denticola, decreased. The relative abundances ofP. gingivalis,Tannerella forsythia,Filifactor alocis, andPrevotella intermediadetermined by qPCR were significantly different among the groups. The three bacterial speciesP. gingivalis,T. forsythia, andF. alociswere positively correlated with the sum of the full-mouth probing depth and were moderately accurate at distinguishing the severity of periodontal disease. In conclusion, the salivary microbiota showed gradual compositional changes according to the severity of periodontitis, and the levels ofP. gingivalis,T. forsythia, andF. alocisin mouth rinse saliva had the ability to distinguish the severity of periodontal disease.IMPORTANCEPeriodontal disease is one of the most widespread medical conditions and the leading cause of tooth loss, imposing high economic costs and an increasing burden worldwide as life expectancy increases. Changes in the subgingival bacterial community during the progression of periodontal disease can affect the entire oral ecosystem, and bacteria in saliva can reflect the degree of bacterial imbalance in the oral cavity. This study explored whether the specific bacterial species in saliva can distinguish the severity of periodontal disease by analyzing the salivary microbiota and suggestedP. gingivalis,T. forsythia, andF. alocisas biomarkers for distinguishing the severity of periodontal disease in saliva.