The Oral Microbiome and Systemic Health: The Connections Redefining Dental Medicine

The oral cavity harbours more than 700 different microbial species forming an ecosystem of remarkable complexity. Far from being a mere surface antibacterial concern, the balance of the oral microbiome now conditions not only dental health, but cardiovascular, neurological and metabolic health too.

The oral cavity harbours more than 700 different microbial species — bacteria, archaea, fungi, viruses — forming an ecosystem of remarkable complexity. Saliva alone contains between 10⁸ and 10⁹ micro-organisms per millilitre. Far from being a mere surface antibacterial concern, the balance of the oral microbiome now conditions not only dental health, but cardiovascular, neurological and metabolic health as well. The discoveries published in Cell Host & Microbe, Nature Microbiology and the Journal of Dental Research since 2022 are sketching a dental medicine profoundly rethought in the light of the microbiome.

1. Oral Dysbiosis: When the Microbiome Shifts Towards Pathology

Oral health corresponds to a state of eubiosis — a dynamic equilibrium between commensal microbial communities. Dysbiosis refers to the tipping of this equilibrium towards a pro-inflammatory and pro-infectious state. In periodontology, the classical "specific plaque" model has been replaced by the polymicrobial dysbiosis model: P. gingivalis, although present in relatively small quantities, acts as a "keystone pathogen" — a key disruptor capable of reorganising the entire microbial community and suppressing the host's local immune responses. This concept, formalised by Hajishengallis (Nature Reviews Microbiology, 2014, >2,400 citations), remains in 2024 one of the most productive conceptual frameworks in periodontal biology.

2. The Oral Microbiome and Cardiovascular Disease: The Mouth-Heart Axis

The association between periodontal disease and cardiovascular disease has been documented since the work of Mattila et al. (1989). The mechanisms identified in 2024 are multiple: transient bacteraemias during chewing or brushing in periodontitis patients, allowing bacteria such as P. gingivalis, S. mutans or F. nucleatum to reach heart valves and atherosclerotic plaques; production of systemic pro-inflammatory metabolites (IL-6, TNF-α, CRP) by immune cells activated by oral bacterial lipopolysaccharides; and the conversion of dietary nitrates to vasodilatory nitrites by nitroreductase commensal bacteria on the tongue (a direct link to blood pressure regulation). A meta-analysis published in the European Heart Journal (2023, n = 1.1 million patients) confirms a Hazard Ratio of 1.24 (95% CI: 1.18–1.30) for major cardiovascular events in patients with severe periodontitis vs. healthy periodontium.

3. The Oral Microbiome–Brain Connection: P. gingivalis and Alzheimer's

One of the most surprising — and widely reported — discoveries of the last decade in oral microbiology concerns the relationship between P. gingivalis and Alzheimer's disease. A study published in Science Advances (Dominy et al., 2019) demonstrated the presence of P. gingivalis and its specific proteases (gingipains) in the post-mortem brains of Alzheimer's patients, correlating with tau and β-amyloid burden. In 2024, two prospective follow-up studies (JAMA Neurology) on cohorts of 65 years and older confirm that severe periodontitis is associated with accelerated progression of cognitive decline (ADAS-Cog difference at 6 years: –2.4 points in the untreated periodontitis group vs the treated group).

4. Implications for Orthodontic Practice and Aligners

These microbiome data have concrete implications for aligner orthodontics. First, aligner wear measurably modifies the oral microbiome: a 2024 study (J. Oral Microbiol.) documents a significant increase in Lactobacillus and Streptococcus mutans under aligners in patients who do not comply with post-meal hygiene — confirming the crucial importance of brushing before reinsertion. Second, the correction of complex malocclusions by aligners improves accessibility to dental surfaces and reduces plaque retention areas — a microbiome benefit documented by reduction in periodontal pathogen populations at 12 months of treatment. Third, for diabetic or cardiovascular patients, periodontal stabilisation prior to orthodontic treatment is not merely a clinical precaution: it is a systemic medicine imperative.