Dentistry and medicine, historically kept apart as if the mouth existed in a separate dimension from the rest of the body, are now being recognised as intrinsically linked. The medieval origins of dentistry as a trade – with barber surgeons pulling teeth, jewellers and blacksmiths crafting dentures – created a divide that persists today in separate training routes, professional bodies and NHS structures. But a growing body of research is forcing cardiologists, diabetes specialists and rheumatologists to pay close attention to what is happening inside their patients’ mouths.
A historical divide
The separation of dentistry from mainstream medicine has deep roots. In the Middle Ages, tooth extractions were performed by barber surgeons, who also handled wound treatment, setting bones and bloodletting, often learning through apprenticeships rather than formal academic study. It was not until 1745 in England that surgeons split from barbers, but dentistry remained a craft rather than a branch of medicine. Today, medical doctors generally cannot act as dentists, and dentists are not medical doctors. The NHS treats them as distinct, with dental care not free at the point of use. Yet that conceptual wall is crumbling as evidence mounts that oral health is a window into systemic health.
The mouth as a gateway: cardiovascular links
“People forget that the mouth is an open portal, a gateway into the bloodstream and your lungs, and inside your body,” says Steve Kerrigan, professor of precision therapeutics at RCSI University of Medicine and Health Sciences’ school of pharmacy and biomolecular sciences in Dublin. Our mouths host about 700 species of bacteria, he explains. Gum disease is extremely common – around half of UK adults have it in some form – caused by bacteria-harbouring plaque building up on teeth. Gingivitis is the milder, reversible version (a tell-tale sign is bleeding when you floss or brush). Periodontitis, the irreversible form, is the main cause of adult tooth loss and is now classified as a chronic inflammatory condition in its own right.
The most advanced research into the mouth-body connection involves cardiovascular disease. Kerrigan notes that some studies have shown “up to 90% of people with cardiovascular disease also have gum disease”. But the key question is causation: are these conditions simply both more common in people with poor general health, or does gum disease directly damage the heart and blood vessels?
It is already well established that oral infections can cause bloodstream infections – which is why patients with replacement heart valves have long been given prophylactic antibiotics before tooth extraction or deep descaling. But oral bacteria can also leach into the bloodstream through rotten teeth or bleeding gums, slowly and imperceptibly damaging the cardiovascular system in other ways.
A condition called atherosclerosis – where cholesterol, fat and calcium build up into plaque on artery walls, restricting blood flow – provides one mechanism. This arterial plaque is different from dental plaque (which is a sticky bacterial film), although both harden over time and are associated with inflammation. “The majority of bacteria in atherosclerotic plaque is from the mouth,” says Kerrigan. Scientists are still working out whether oral bacteria enter the bloodstream and directly cause atherosclerosis to develop, or whether the plaque forms through another mechanism but is sticky, so bacteria from the mouth adhere to it once they enter the bloodstream. Either way, once the bacteria are present, they increase inflammation and create further health problems.
There is a more direct risk: blood clots and strokes. “Once these bacteria breach the barriers in the mouth, they get into the bloodstream, and they can bind to the blood clotting cells, called platelets,” Kerrigan explains. Platelets help stop bleeding when we cut ourselves. “When these bacteria bind to platelets, it causes them to stick together the exact same way as when you cut yourself. What that means is that you’ve got a clot circulating in your bloodstream, and that clot will eventually get stuck in a small blood vessel. And if that small blood vessel is feeding the brain, then you end up with either a transient ischemic attack – a mini-stroke – or a full-blown stroke.” If the clot gets stuck in a vessel in the heart, he says, “you can suffer a heart attack as well”. When a clot forms on the heart valves, “that leads to a condition called infective endocarditis. This prevents your valve closing properly, which can lead to heart failure. These things are quite well recognised.” Nearly all of the bacteria found that trigger these clots are oral bacteria, says Kerrigan.
Diabetes and beyond: the two-way street
Diabetes is another condition with a fairly well-established bidirectional link with oral health. One of the latest developments was recorded in a 2025 study, which found that having root canal treatment significantly lowered blood sugar levels (diabetes is characterised by excessively high blood sugar). Root canal treatment also lowered blood cholesterol and fatty acid levels, providing an additional boost for heart health. This finding suggests that removing damaged or infected pulp deep inside a tooth, and sealing the roots, could not only save your tooth but also help protect against type 2 diabetes.
The connection works both ways. Systemic inflammation from oral infections can disrupt blood sugar control, making gum disease a risk factor for developing diabetes. Conversely, if you have diabetes and your blood glucose levels are persistently elevated, you become more vulnerable to gum disease. “People with gum disease or periodontitis and diabetes have a three times higher mortality risk than those without gum disease,” says Kerrigan.
Rheumatoid arthritis also shows a circular relationship. RA-driven systemic inflammation can disrupt the oral microbiome, fostering harmful bacteria that lead to gum disease, and those bacteria in turn exacerbate oral inflammation, which fuels RA. Patients with rheumatoid arthritis often have higher levels of antibodies against oral pathogens such as Porphyromonas gingivalis, which is linked to RA autoimmunity. Treating gum disease has been shown to reduce inflammation and improve RA symptoms. RA can also cause jaw problems and dry mouth due to reduced saliva, further impacting oral health, and smoking is a significant risk factor for both conditions.
Dementia is under active investigation, though no causal link has been proved, says Jing Kang, a senior lecturer in medical statistics at the faculty of dentistry, oral and craniofacial sciences at King’s College London. A 2016 study by Kang’s colleagues found that the presence of gum disease was associated with a six-fold increase in the rate of cognitive decline over six months. The study also found that, over the follow-up period, gum disease was associated with “a relative increase in the pro-inflammatory state”, which leaves us more vulnerable to major illnesses – from cancers to neurodegenerative and metabolic diseases to depression.
One theoretical route, says Kang, is that “it is all related to the immune response and inflammation”. But it is hard to pinpoint a precise causal mechanism, and there could be many: “It is possible that behaviours, such as our choice of food or choice of lifestyle, could also impact on our oral health.” Cardiovascular disease and chronic metabolic diseases associated with oral health could be affecting brain degeneration, too. Poor education in childhood could be a factor, leading to worsening oral health gradually over time; then, when we are older, the resulting inflammation affects cognitive function. “There are all sorts of hypotheses, but it’s hard to prove and further studies are needed,” Kang says.
Kang and her colleagues are working towards establishing whether treating oral health issues promptly “would prevent or delay cognitive decline”. They are only at the small, proof-of-concept study stage so far – but, she says, it is never too late to take better care of our mouths. Meanwhile, she says, gum pain could be seen as a potential window into what is happening inside the body. The evidence for the oral-brain axis so far relates more to gum disease than to the teeth themselves, but in terms of oral care, the two go together.
Beyond these specific conditions, oral health affects quality of life in ways that can themselves harm overall health. Advanced gum disease and tooth decay can be painful, smelly and unsightly. “Oral health is reflected in how we feel, our appearance, our confidence,” Kang says. When her team has studied this, “people who are suffering from gum disease are less confident and don’t want to socialise, compared with people who have healthy teeth. That may affect the brain or other parts of the body. And because of the pain and inflammation, people need to take more medication – and some medication has side effects on oral health because it reduces saliva generation. So everything is interlinked.”
According to Kang’s research, brushing twice a day and flossing wherever possible may even help fix your aching knees. “People who had arthritic knees were more likely to have had gum disease, and vice versa. People suffering from more gum disease were diagnosed [with arthritis]; or they saw deterioration much quicker than those who had healthy teeth.”
None of this means we should panic. Kang is careful to point out that this is all statistical evidence, “from the population level. It does not apply to individuals. So don’t worry too much, if when brushing your teeth there’s blood, that you’re going to get dementia the next day. It is just a message to deliver to the public to keep our teeth and gums healthy.”
Access, affordability and the reality of NHS dentistry
The government’s last oral health survey, in 2021, found that a quarter of adults with natural teeth reported teeth, fillings, crowns or fixed bridges that were damaged, cracked or broken. But getting emergency help, or even treatment, on the NHS is increasingly hard. In April 2025, only 20.5% of those who tried to get an NHS appointment were successful, with 81.4% receiving no care at all. Data from October 2024 indicated that up to 97% of new patients were unable to access NHS dentistry. Access varies significantly by region, and a third of adults reported that the cost of dental care affected the type of treatment they received; a quarter had delayed dental care due to cost.
Reports of people self-treating and even pulling out their own teeth have emerged. And, as Kerrigan says, even if a tooth is taken out professionally, “a vast majority of people won’t be able to afford implants to replace that tooth, so everything changes in your mouth. If you don’t have teeth, the microbiome in your mouth is going to change. And we already know that the bacteria that are in your mouth are critically important because they are the first step in digestion.” NHS funding for dental implants is limited to specific clinical situations with a clear medical need; private implants can cost from £1,900 to £3,500 for a single implant, with full-mouth restorations costing tens of thousands of pounds.
Preventative advice: what can we do?
“You’re meant to brush your teeth at least twice a day, morning and evening,” says Kerrigan. “That’s the bare minimum, but during the day is great as well, if you can do that.” He says electric toothbrushes with rotating heads “are probably much better for moving and pulling the bacteria off your teeth”. Flossing and cleaning between your teeth are also recommended.
“Diet plays a really important role here as well,” he says. “When you snack, it’s [likely] going to be on sugary foods. So obviously, the more sugar you put into your mouth, the more you’re feeding the bacteria. You want to avoid that as much as possible, because the more bacteria, the more damage they’re going to do to your teeth and to your gums. But again, you have to look at the person.”
Maintaining good oral hygiene is part of an overall healthy lifestyle. As Kerrigan puts it: “The person who runs several times a week – they probably have perfect oral hygiene as well. And if you look after one part of your body, you tend to look after all parts of your body.”
