Abstract

Background: Dental caries remains a globally prevalent chronic oral disease among adolescents. Contemporary understanding recognizes caries as a microbiome-driven dysbiotic process rather than a mono-infection. However, detailed characterizations of oral microbiome diversity patterns across stratified caries risk levels in adolescent populations remain insufficiently explored using modern high-throughput sequencing technologies. Objective: This study aimed to evaluate oral microbiome diversity, composition, and structural differences among adolescents stratified into low, moderate, and high caries risk groups, and to identify microbial biomarkers distinguishing these risk categories. Methods: A cross-sectional study was conducted on 210 adolescents aged 12–18 years, stratified into three equal groups (n = 70 each) based on CAMBRA (Caries Management by Risk Assessment) protocols. Unstimulated saliva and supragingival plaque samples were collected and subjected to 16S rRNA gene sequencing targeting V3–V4 hypervariable regions on the Illumina MiSeq platform. Alpha diversity (Shannon, Simpson, Chao1), beta diversity (weighted UniFrac, Bray-Curtis), and differential abundance analyses were performed. Results: Shannon diversity index decreased significantly from the low-risk group (4.32 ± 0.42) through moderate-risk (3.61 ± 0.39) to high-risk (2.76 ± 0.51) groups (p < 0.001). Beta diversity analyses demonstrated distinct microbial clustering among risk categories (PERMANOVA R² = 0.213, p = 0.001). Streptococcus mutans relative abundance was significantly elevated in high-risk adolescents (21.34 ± 6.12%) compared with low-risk (3.87 ± 1.96%) (p < 0.001). Conversely, health-associated genera including Neisseria, Rothia, and Corynebacterium showed significant depletion in high-risk participants. Logistic regression identified S. mutans abundance (OR = 3.82, 95% CI: 2.14–6.81) and Shannon index (OR = 0.38, 95% CI: 0.21–0.67) as independent predictors of high caries risk. Conclusion: Oral microbiome diversity demonstrates progressive decline with increasing caries risk among adolescents, accompanied by characteristic compositional shifts from commensal-dominated to pathobiont-enriched communities. These microbial signatures hold potential as adjunctive biomarkers for enhanced caries risk prediction.