LAUSR

ABSTRACT Aim This study aimed to compare the microbial communities across four oral sample types—saliva, oral rinse, subgingival plaque and gingival crevicular fluid (GCF)—and to identify disease‐associated microbiota in periodontitis. Methods Oral samples were collected from 150 adults, each providing four types of samples in the same visit. Saliva (5 mL) and oral rinse (10 mL, 30‐s swish) were collected prior to clinical examination. Subgingival plaque was sampled using a curette from the two deepest pockets, followed by GCF collection via 20‐s insertion of gingival retraction cords at the same sites. All samples underwent 16S rRNA (V3–V4) sequencing. Site‐specific microbial profiles were evaluated across all participants. For disease comparisons, only individuals with clear periodontal status (periodontally healthy, n = 41; stage III/IV periodontitis, n = 43) were included, excluding stage I/II cases (n = 66). Results Saliva and oral rinse formed one microbial cluster; plaque and GCF formed another. Alpha diversity was found increased in disease, except in GCF. Beta diversity showed the most distinct disease‐related shift in GCF. Red complex pathogens and GCF‐specific differentially abundant taxa were markedly enriched in periodontitis. Conclusions GCF yielded the clearest microbial differentiation between health and periodontitis, supporting its diagnostic utility.