Effect of Probiotic Supplementation on Cariogenic Streptococcus mutans Levels: A Systematic Review and Network Meta-Analysis.

OBJECTIVE

To systematically evaluate and quantitatively compare, through pairwise and network meta-analysis, the effectiveness of probiotic supplementation in reducing cariogenic Streptococcus mutans levels in human subjects.

METHODS

A comprehensive search was conducted in PubMed, Scopus, Embase, Web of Science and Cochrane Library up to October 2025. Randomised controlled trials assessing probiotic or synbiotic formulations with quantitative S. mutans outcomes were included. Data expressed as mean ± standard deviation were synthesised under a random-effects model using a frequentist network meta-analysis (netmeta, R). Effect sizes were reported as mean differences (MD, 95% CI). To strengthen analytical validity, all outputs were cross-validated through triangulation using the MetaInsight platform, confirming consistency between independent computational environments. Risk of bias was assessed with RoB 2, and evidence certainty was appraised via CINeMA.

RESULTS

Twenty trials fulfilled inclusion criteria. Most interventions showed a short-term reduction in S. mutans counts, but differences versus placebo were small and not statistically significant across intervals. Forest-plot synthesis and triangulated results indicated that effects were transient and strain-dependent. SUCRA rankings suggested a high percentage of success, but those findings are only probabilistic, not conclusive superiority. Overall evidence certainty was low to moderate.

CONCLUSIONS

Probiotic supplementation exhibited a limited, time-dependent capacity to modulate S. mutans levels without a consistent advantage over placebo. Current findings support its role as a safe adjunctive rather than as a standalone preventive strategy.

CLINICAL SIGNIFICANCE: Within the available evidence, probiotics should be regarded as experimental adjuncts rather than as replacements for conventional caries-prevention measures. Any observed microbiological benefits were modest, transient and strain-specific, without consistent translation into clinical outcomes. Their recommendation should remain cautious until larger, long-term randomised trials confirm durable effects.

TRIAL REGISTRATION: PROSPERO registration number: CRD420251180536.