Oral microbiome alterations in individuals with type 1 diabetes: a systematic review

To systematically evaluate associations between glycemic control and oral microbial findings in individuals with type 1 diabetes mellitus (T1DM), distinguishing targeted detection of selected taxa from comprehensive oral microbiome profiling.

A systematic search of PubMed, Embase, and Scopus was conducted from database inception to June 2025 in accordance with the PRISMA statement. The protocol was prospectively registered in PROSPERO. Human studies investigating the relationship between glycemic control and the oral microbiome in individuals with T1DM were eligible for inclusion. Two reviewers independently performed study selection, data extraction, and risk of bias assessment. Due to substantial methodological heterogeneity, findings were synthesized qualitatively.

Forty-two studies met the eligibility criteria. Most were cross-sectional and assessed glycemic control using glycated hemoglobin (HbA1c), with heterogeneous thresholds. Saliva and subgingival plaque were the most frequently sampled oral sites. Targeted studies commonly reported associations between poorer glycemic control and selected periodontal pathogens or oral Candida carriage, whereas findings for cariogenic microorganisms were inconsistent. Only four studies used comprehensive culture-independent community profiling; these studies reported differences in community composition and/or diversity, but the small number and methodological heterogeneity preclude a uniform conclusion regarding the direction of diversity change.

Poorer glycemic control is associated with selected oral microbial alterations in individuals with T1DM, particularly in periodontal and Candida-focused studies. However, the predominance of targeted assays, cross-sectional designs, and substantial methodological heterogeneity limits conclusions about whole-community oral microbiome dysbiosis or causality. Well-designed longitudinal studies using standardized clinical phenotyping and comprehensive microbiome profiling are needed.

Poor glycemic control may coexist with adverse oral microbial and clinical findings in individuals with T1DM. These associations support attention to established preventive dental care and periodontal assessment as part of multidisciplinary diabetes care; however, oral microbiome monitoring is not yet validated as a clinical biomarker of glycemic status or oral disease risk.