Behavioral and Microbial Differences in Dental Caries among 5-Year-Old Children in Urban and Rural Yunnan: A Multifactorial Machine Learning Study

Objective Yunnan, southwestern China, experiences uneven economic development and an unbalanced distribution of medical resources. Herein, 5-year-old children from Hongta District (urban) and Fengqing County (mountainous) were recruited to investigate oral health conditions. After integrating oral health behavior surveys with plaque microbiome analysis, machine learning identified influencing factors and microbial communities, facilitating diagnostic model construction and revealing how regional disparities affect dental caries in children. Methods We randomly selected 30 caries-free (CF group) and 30 caries-affected (DC group) 5-year-old children from each location and conducted oral epidemiological examinations, oral health behavior questionnaires, and 16S rRNA sequencing of dental plaque samples. Behavioral differences and genus-level microbial abundance were compared across locations. Random forest models analyzed high-risk factors, identified key microbial communities, and assessed diagnostic performance. Results Questionnaire analysis revealed significant differences between the DC and CF groups in location, dessert consumption frequency, and nighttime postbrushing sugar intake (NPSI). By location, Fengqing County and Hongta District differed significantly in NPSI and fluoridated toothpaste use. Plaque analysis showed significant phylum-level differences between the DC and CF groups for Bacteroidetes , Fusobacteria , and Proteobacteria . A phylum-level diagnostic model highlighted Fusobacteria as a diagnostic marker [area under the curve (AUC): 0.737]. Least absolute shrinkage and selection operator analysis identified three key genera—namely Capnocytophaga , Haemophilus , and Comamonas —with Capnocytophaga aiding diagnosis (AUC: 0.720). Adding location, dessert consumption, and NPSI to the model further improved diagnostic performance (AUC: 1). Conclusion Regional socioeconomic disparities influenced dental caries prevalence in 5-year-old children, reflected in behavioral and microbial differences.