The Role of the Oral Microbiome and Dental Caries in Respiratory Health: A Systematic Review

Objectives: This systematic review aimed to evaluate the association between oral health—particularly dental caries and dysbiosis of the oral microbiome—and respiratory diseases across different age groups and clinical settings, with emphasis on microbial overlap, clinical outcomes, and preventive strategies. Methods: A systematic search was conducted in PubMed, Scopus, Embase, Web of Science, and the Cochrane Library up to June 2025. Eligible studies included randomized controlled trials, cohort, case–control, and cross-sectional investigations examining the relationship between oral diseases or microbiome alterations and respiratory outcomes. Data on study design, population, oral health parameters, microbial taxa, and respiratory endpoints were extracted. Study quality was assessed using the Mixed Methods Appraisal Tool (MMAT, 2018). Results: Twenty studies met the inclusion criteria, encompassing pediatric, adult, and elderly populations. Poor oral health, reflected by higher caries indices and periodontal inflammation, was consistently associated with increased risk of lower respiratory tract infections (LRTI), aspiration events, ventilator-associated pneumonia (VAP), and impaired pulmonary function. Oral microbiome analyses revealed enrichment of Veillonella, Prevotella, Klebsiella, and Pseudomonas species in both oral and airway samples, supporting the oral cavity as a reservoir for respiratory pathogens. Interventional evidence from intensive care and nursing home settings demonstrated that structured oral care—particularly daily toothbrushing and chlorhexidine-based plaque control—significantly reduced pneumonia incidence. Conclusions: This review confirms a clinically relevant and biologically plausible link between oral dysbiosis, dental caries, and respiratory disease. Oral biofilms contribute to infection risk through microaspiration and microbial seeding of the lower airways. Integrating oral screening, hygiene maintenance, and treatment of active oral disease into respiratory care pathways may reduce respiratory morbidity and mortality, particularly among high-risk populations such as ICU patients, older adults, and individuals with chronic lung disease.