Association between oral microbial diversity and periodontitis in a nationally representative U.S. population: A cross‐sectional study

Background To investigate the association between salivary oral microbiome diversity and periodontitis in a nationally representative U.S. population. Methods A total of 5323 participants with both periodontal examination and oral microbiome data from NHANES 2009–2012 were included. Periodontitis was defined using 2012 CDC/AAP criteria. Four alpha diversity indices (operational taxonomic unit [OTU] richness, Faith's phylogenetic diversity [FPD], the Shannon‐Weiner index [SWI], and the inverse Simpson index [ISI]) were calculated. Beta diversity metrics (Bray–Curtis, weighted and unweighted UniFrac) were assessed using PERMANOVA for group comparisons and hierarchical clustering to identify subgroups. Ordered logistic regression was employed to examine the associations between periodontitis severity and microbial alpha diversity, beta diversity clusters, and bacterial genus abundances. Results Higher alpha diversity was positively associated with greater periodontitis severity (OTU richness: OR = 1.01, 95%CI: 1.01–1.02; FPD: OR = 1.21, 95%CI: 1.19–1.24; SWI: OR = 2.03, 95%CI: 1.81–2.30; ISI: OR = 16.61, 95%CI: 1.75–157.59). Beta diversity analyses revealed significant community compositional differences across periodontitis severity levels (PERMANOVA, all p = 0.001). Hierarchical clustering identified distinct microbial subgroups with varying odds of belonging to more severe periodontitis levels. Eighty‐two bacterial genera were significantly associated with periodontitis, including taxa showing strong positive associations consistent with the red and orange complexes (e.g., Porphyromonas, Tannerella, Treponema ) and taxa exhibiting negative associations involving health‐associated genera (e.g., Rothia , Veillonella ). Conclusions Salivary microbiome diversity, particularly higher alpha diversity and specific beta diversity clusters, was associated with periodontitis severity, supporting its potential relevance as a non‐invasive indicator of periodontal health status. Plain language summary This national study examined the relationship between the types and quantities of microbes present in saliva and the severity of periodontitis in more than 5,300 U.S. adults. We found that the more diverse the microbial community in a person's saliva—meaning a greater variety and number of different types—the more severe their periodontitis tended to be. We also found that the composition of these microbes differed depending on the severity of the periodontitis. Specifically, certain clusters of microbes, including well‐known disease‐causing bacteria such as Porphyromonas and Treponema (often called the red and orange complexes), were strongly associated with more severe periodontitis. Conversely, other common, generally healthy bacteria were less abundant. These findings suggest that analyzing the diversity and composition of microbes in saliva could be a valuable, noninvasive way to check for and potentially monitor the severity of periodontitis.