Beyond H. pylori: Re-Examining the Oral Microbiome's Role in Gastric Health and Disease, a Narrative Review.

Background: The separation between oral and systemic health is increasingly challenged. Globally prevalent inflammatory diseases such as gastritis, often caused by Helicobacter pylori (H. pylori), and oral pathologies like periodontitis may be interconnected through microbial and inflammatory pathways. Objective: This review synthesizes evidence on the dental-gastric link, examining mechanistic pathways and clinical implications. Methods: A structured literature search identified key studies from 2000 to 2025, prioritizing systematic reviews and high-quality human research. Findings: Three key mechanistic pathways link oral dysbiosis with gastric pathology: (1) the direct translocation of oral pathogens to the stomach, including H. pylori and the broader dysbiotic oral microbiome; (2) the systemic inflammatory spillover from the periodontium, which primes the host immune system and exacerbates gastric inflammation; and (3) ancillary mechanisms such as the disruption of beneficial nitrate-nitrite-nitric oxide metabolism. Epidemiological studies show strong associations, and initial interventional trials indicate periodontal therapy may improve H. pylori eradication rates and reduce recurrence. However, the evidence is tempered by methodological limitations, including profound confounding by shared risk factors (e.g., smoking, socioeconomic status), the challenge of reverse causality, and inconsistent results from interventional studies. Conclusion: While confounding factors require consideration, oral health is a promising modifiable risk factor for gastritis. Interdisciplinary collaboration between dentistry and gastroenterology is essential to advance research and integrate oral care into gastrointestinal disease management.