Associations between the oral microbiome, age, and cumulative dental caries experience: a cross-sectional study

Objectives: Age is consistently associated with higher cumulative caries experience, but whether age-related oral microbiome shifts contribute to this association remains unclear. This study characterized age-related oral microbiome alterations, developed a microbial health index, and explored the interplay between the microbiome, age, and caries experience in adults. Materials and methods: Among 4,763 participants aged ≥ 14 years from the National Health and Nutrition Examination Survey (NHANES), caries experience was quantified using the Decayed, Missing, and Filled Surfaces (DMFS) index. Oral microbiomes were profiled by 16 S rRNA sequencing. Restricted cubic splines, diversity and network analyses, random forest modeling for an Oral Microbial Health Index (OMHI), and mediation analysis were used to examine relationships among age, microbiome, and caries. Results: Age explained 40.5% of DMFS variance with a non-linear positive correlation (P < 0.001). Microbial α-diversity declined non-linearly with age and DMFS (P < 0.001). Community structure and networks differed across age groups and caries experience levels. OMHI discriminated caries-free from high-burden individuals (AUC = 0.789), and the OMHI-based mediation accounted for 23.8% (95% CI: 21.3%–26.2%) of the age–DMFS association. Conclusions: The microbiome mediates a substantial portion of the age–caries association. Age-related shifts in diversity, taxonomy, and network structure are associated with greater caries burden. The OMHI shows promise as a non-invasive tool for caries risk stratification and age-specific prevention. Clinical Relevance: These findings support microbiome-informed, age-stratified caries prevention and offer a non-invasive indicator for identifying adults at elevated risk in clinical and public health settings.