The forgotten organ: Why the oral microbiome belongs in every physician's toolkit

The oral cavity is the most densely colonised microbial niche in the human body after the gut – over 700 species and an estimated two billion bacteria (Deo and Deshmukh, 2019) – yet it remains conspicuously absent from the systemic health conversation. Mounting evidence links oral microbial dysbiosis to more than 50 systemic conditions (Peng et al , 2022), including cardiovascular disease, type 2 diabetes (Preshaw et al , 2026), adverse pregnancy outcomes, rheumatoid arthritis and Alzheimer's. Despite this, dentistry and medicine continue to operate as parallel systems, with oral health excluded from most general health screens, NHS commissioning structures and undergraduate medical curricula. This narrative review analyses current evidence on the oral microbiome and oral-systemic disease, outlines three biological mechanisms by which the oral cavity drives systemic disease, and sets out five practical, author-proposed steps physicians can take to integrate oral health into routine practice. The case for action is no longer scientific – it is structural.