Association between obstructive mouth breathing and oral microbiota in children: a cross-sectional study

Background Obstructive mouth breathing (OMB) is a common pediatric condition related to multiple systemic and oral health problems, but its impact on the oral microbiota remains unclear. This study aimed to investigate the association between oral microbiota and OMB in children and to identify potential microbial biomarkers. Methods In this cross-sectional study, 23 children with OMB and 16 age-matched nasal breathing (NB) controls were included. Mixed oral swab samples were collected from multiple anatomical sites (tongue, buccal mucosa, palate, and tonsils) and analyzed by 16S rRNA gene sequencing. Alpha diversity was analyzed using the Wilcoxon rank-sum test, and beta diversity was evaluated using Principal Coordinate Analysis (PCoA) and PERMANOVA. Linear Discriminant Analysis Effect Size (LEfSe) was employed to identify differentially abundant taxa, and a Random Forest model was constructed to distinguish the groups. Results Compared with controls, children with OMB exhibited significant oral microbial dysbiosis, which was characterized by reduced alpha diversity (Sobs, Chao1, ACE, and Pd indices; all P  < 0.05). Importantly, this decline in microbial diversity was negatively correlated with the clinical severity of OMB. PCoA and PERMANOVA indicated that the microbial composition of the two groups was significantly different (unweighted UniFrac; R² = 0.065, P  = 0.003). LEfSe identified 13 differentially abundant taxa (LDA score > 3.0, P  < 0.05). The relative abundances of Moraxella and Corynebacterium were significantly decreased in the OMB group, while Actinomyces , Acinetobacter , Cupriavidus , and Roseateles were significantly enriched. Moreover, the Random Forest model based on 11 key genera effectively distinguished OMB from NB children (AUC = 0.94). Conclusions This study systematically reveals the characteristic oral microbiota dysbiosis in pediatric OMB. These findings provide a new microbiological perspective on the pathophysiological mechanisms of OMB in children. The diagnostic model shows great potential as a non-invasive screening tool. Future large-scale longitudinal studies are needed to verify its clinical diagnostic value and clarify the causal relationships between microbial changes and disease progression.