Association between dental flossing frequency and oral microbiome in U.S. adults

Background The oral microbiome is vital for health, yet population-based evidence on how self-reported flossing relates to microbial communities remains limited. This study examined the association between self-reported dental flossing frequency and oral microbiome diversity in a nationally representative sample of U.S. adults.Methods This cross-sectional analysis included 4,772 adults aged 30-69 from NHANES 2009–2012. Flossing frequency was categorized as non-users (0 days/week), some flossing (1-6 days/week), and daily users (7 days/week). Oral microbiome composition was profiled using 16S rRNA sequencing. α-diversity was calculated using Observed amplicon sequence variants (ASVs), Shannon, Inverse Simpson, and Faith’s Phylogenetic Diversity (PD); β-diversity using Bray–Curtis and UniFrac distances. Survey-weighted linear regression and PERMANOVA were used with covariate adjustment.Results Participants included, non-users (32%), some flossing (38%), and daily users (30%). A dose–response relationship was observed between flossing frequency and reduced microbial richness and phylogenetic diversity. Compared with non-users, daily users exhibited significantly lower richness (Observed ASVs: β = −11.46, 95% CI: −15.62 to −7.29) and phylogenetic diversity (Faith’s PD: β = −0.88, 95% CI: −1.20 to −0.56). Daily flossing was associated with a modest reduction in Shannon diversity, with no significant association for the Inverse Simpson index. Inverse associations were more pronounced among younger and lower-income adults, but not among current smokers. β-diversity differed significantly across groups, although effect sizes were minimal (Bray–Curtis R2 = 0.059%; unweighted UniFrac R2 = 0.090%).Conclusions Frequent flossing was associated with reduced microbial richness and phylogenetic diversity, potentially indicating a favorable shift toward a healthier microbial community.