Oral health

Periodontitis begins when bacterial plaque along the gumline triggers inflammation of the gums (gingivitis). If it persists, the inflammation extends below the gumline, forming deep pockets between tooth and gum and gradually destroying the bone that anchors the teeth. Bleeding, receding gums and loosening teeth are typical signs. The disease is chronic and often painless, so it can progress for years before teeth are lost.

Tooth loss reflects the combined burden of decay and periodontitis over a lifetime; these two dental diseases together account for about 2% of the global burden of human disease [1]. For this reason many studies use the number of remaining teeth as a practical measure of long-term oral disease, alongside clinical measures such as pocket depth and loss of bone around the teeth.

A systematic review prepared for the US Preventive Services Task Force identified seven good or fair quality cohort studies of adults without known heart disease. Summary relative risks (the risk in one group relative to another; 1.24 means 24% higher) for coronary heart disease ranged from 1.24 (95% confidence interval 1.01 to 1.51) to 1.34 (1.10 to 1.63), depending on whether periodontal disease was defined by periodontitis, tooth loss, gingivitis or bone loss. The association held after adjustment for traditional risk factors and socioeconomic status [3]. A joint workshop of the European Federation of Periodontology and the World Heart Federation reviewed the epidemiological and mechanistic evidence and concluded that there are significant associations between periodontitis and cardiovascular disease [2]. Heart disease in general is covered under cardiovascular disease.

Oral hygiene habits have been studied for heart rhythm and pump function. In 161,286 adults from Korea's National Health Insurance Service cohort followed for a median of 10.5 years, brushing three or more times a day was associated with a 10% lower risk of atrial fibrillation (hazard ratio 0.90) and a 12% lower risk of heart failure (0.88), after adjustment for age, exercise, smoking, alcohol, diabetes, blood pressure and other factors. Professional dental cleaning was associated with a 7% lower risk of heart failure (0.93), and having 22 or more missing teeth with a 32% higher risk (1.32) [6].

A systematic review of 75 cohort studies, 44 of which were pooled, found that a lower number of teeth was associated with higher risk of atherosclerotic cardiovascular disease and of death. Pooled adjusted hazard ratios (a measure of how fast events occur in one group relative to another) for all-cause mortality ranged from 1.02 to 1.30 across analyses, and pooled risk ratios for the cumulative incidence of death ranged from 1.76 to 2.27 [1]. The wide range reflects differences in how studies counted teeth and defined comparison groups.

An earlier review asked whether replacing lost teeth changes mortality. No study had tested this directly; using denture use as a proxy, two moderate-quality studies suggested an effect on all-cause mortality, but an effect on circulatory mortality was not established [8].

A 2022 systematic review of 47 longitudinal studies found that poor periodontal health (periodontitis, tooth loss, deep gum pockets or loss of bone around the teeth) was associated with dementia (hazard ratio 1.21, 95% confidence interval 1.07 to 1.38) and cognitive decline (odds ratio 1.23). Complete tooth loss carried a hazard ratio for dementia of 1.23. The authors rated the overall quality of evidence as low and concluded that the associations were at least partly due to reverse causality [4].

A separate dose-response analysis (one that estimates how risk changes with the amount of exposure) of 14 studies and 34,074 participants found that people with more tooth loss had 1.28 times the risk of dementia and 1.48 times the risk of cognitive impairment. Each additional lost tooth added about 1% to the relative risk of dementia, and people with no natural teeth had 1.40 times the risk. Among people who used dentures, the association was not statistically significant [7].

The strongest causal evidence comes from a randomised trial in which 120 patients with severe periodontitis received either community-based periodontal care (59 patients) or intensive periodontal treatment (61). Blood vessel function was measured by flow-mediated dilatation, the widening of the brachial artery in the arm in response to increased blood flow. Twenty-four hours after intensive treatment, dilatation was 1.4 percentage points lower than in the control group and inflammatory markers such as C-reactive protein and interleukin-6 were higher, an acute inflammatory response to the treatment itself. By 60 days the intensive group had better dilatation (by 0.9 percentage points) and by 180 days by 2.0 percentage points (95% confidence interval 1.2 to 2.8). The degree of improvement tracked improvement in gum health, and no cardiovascular events occurred [5]. The trial measured a surrogate marker of vascular health, not heart attacks, strokes or deaths.

Two main pathways have been proposed. Poor oral hygiene can cause transient bacteraemia (bacteria entering the bloodstream) and systemic inflammation, both of which are thought to contribute to atrial fibrillation and heart failure [6]. Periodontitis is a potential source of the chronic low-grade inflammation that is implicated in coronary heart disease [3, 2]. The broader role of chronic inflammation in aging is described under inflammation.

For dementia, the most detailed evidence concerns Porphyromonas gingivalis, the keystone bacterium of chronic periodontitis. The bacterium and its toxic protease enzymes, called gingipains, were identified in the brains of people with Alzheimer's disease, and gingipain levels correlated with tau and ubiquitin pathology. In mice, oral infection with P. gingivalis led to colonisation of the brain and increased production of amyloid beta 1-42, a component of amyloid plaques. Small-molecule gingipain inhibitors reduced the bacterial load in the brain, reduced neuroinflammation and protected neurons in the hippocampus [9]. These are laboratory and animal findings and do not establish that the bacterium causes Alzheimer's disease in humans.

Full deep dive: oral care and lifespan.

Almost all of the evidence linking oral health with heart disease, dementia and death is observational. People with poor oral health are more likely to smoke, to have diabetes and to have lower incomes, and although studies adjust for these factors, residual differences remain. The dementia reviews rated their own evidence as low to moderate quality and highlighted reverse causation: early, undiagnosed cognitive decline makes brushing and dental visits less regular, which would produce the same association without gum disease causing dementia [4, 7].

Measures of oral health also vary widely between studies, from self-reported tooth counts to clinical pocket depths, which widens the range of estimates [1]. The only randomised evidence concerns a surrogate measure of blood vessel function over six months [5], and no trial has shown that treating gum disease or replacing teeth reduces heart attacks, dementia or mortality [8].