Influence of Early Feeding Practices on Oral Microbiota Composition During Infancy and Potential Implications for Early Childhood Caries: A Systematic Review

Background: Early feeding practices are among the most influential determinants of the infant oral microbiota during the first years of life. Breastfeeding provides bioactive components—immunoglobulins, human milk oligosaccharides (HMOs), and commensal bacteria—that may shape microbial colonisation patterns with long-term implications for oral health. However, the nature, magnitude, and clinical relevance of these effects remain poorly characterised, particularly with regard to early childhood caries (ECC) risk. Objectives: The primary objective was to evaluate the association between early feeding practices and oral microbiota composition during infancy. A secondary exploratory objective was to assess whether feeding-associated microbiota differences had been linked to subsequent dental caries outcomes. Methods: A systematic review was conducted in accordance with PRISMA 2020 guidelines. PubMed, Scopus, Web of Science, and Embase were searched from January 2010 to June 2026. Eligible studies compared at least two feeding groups and measured oral microbiota directly using culture-independent methods (16S rRNA gene sequencing, metagenomics, or quantitative PCR targeting multiple taxa). Study selection, data extraction, and risk of bias assessment using the ROBINS-E tool were performed independently. Qualitative synthesis was conducted given clinical and methodological heterogeneity. Results: Of 8582 records identified, 12 studies met the inclusion criteria (sample size range: 12–448 participants; age range at microbiota assessment: 2 days–14 years, although eligibility was based on feeding exposure during infancy; six countries). Most included studies reported differences in oral microbiota composition associated with feeding type. During the first months of life, breastfed infants generally showed lower oral microbial diversity and higher abundance of Lactobacillus, the Streptococcus mitis group and Bifidobacterium compared with formula-fed infants, who exhibited greater alpha diversity, higher transmission of maternal oral bacteria, and higher abundance of Prevotella and Actinomyces. Effects were most pronounced in the first three months of life and attenuated by 12 months in most cohorts. Only one study reported subsequent dental caries outcomes after early-life microbiota assessment, finding that Streptococcus cristatus abundance at three months was associated with dental caries at nine years of age, and that longer breastfeeding duration (≥12 months) was associated with a distinct microbiota profile and lower caries rates in this single available longitudinal study. Risk of bias was low in two studies, moderate in six, and high in four. Publication bias could not be formally evaluated. Conclusions: Early feeding practices are associated with measurable differences in oral microbiota composition during infancy, particularly during the first months of life. However, evidence linking these microbiota differences to subsequent dental caries outcomes remains extremely limited, with only one included study assessing later caries development. Therefore, the clinical significance of feeding-associated microbiota profiles remains uncertain and should be investigated through well-designed prospective longitudinal studies.