It is a curious fact that dentistry and medicine have historically been treated as separate fields. The mouth, it seems, is often considered apart from the rest of the body. In the UK, visiting a dentist feels more like a lifestyle choice or cosmetic add-on, and even when an NHS dentist is available, the service is not free at the point of use, unlike medical doctors.
The historical roots of this divide lie in the Middle Ages, when dentistry emerged as a trade. Tooth extractions were performed by barber surgeons, while dentures were crafted by jewellers and blacksmiths. Today, dentistry and medicine still maintain separate training paths, professional bodies, and NHS structures. Generally, medical doctors cannot act as dentists, and dentists are not medical doctors. However, this conceptual separation is gradually eroding, as the links between oral health and systemic health become increasingly evident.
The Mouth as a Gateway
Cardiologists and doctors treating type 2 diabetes are now paying close attention to their patients' oral health. Specialists in conditions ranging from rheumatoid arthritis to cognitive decline may soon follow suit, based on recent research. '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 in Dublin. Our mouths host approximately 700 species of bacteria. Gum disease, caused by plaque buildup, is extremely common: about half of UK adults have some form of it. Gingivitis is the milder, reversible version, often indicated by bleeding when flossing or brushing. Periodontitis is a more severe, irreversible condition where inflammation leads to teeth detaching from gums, and it is the main cause of adult tooth loss.
'Gum disease is now classed as a chronic inflammatory condition in its own right,' says Kerrigan, 'up there with asthma, COPD, Crohn's disease, and ulcerative colitis.' Some studies have shown that up to 90% of people with cardiovascular disease also have gum disease. Research into the relationship between the two is the most advanced in terms of investigating oral and systemic health, demonstrating some actual causation rather than mere association. This is a crucial question: knowing that people with gum disease are more likely to have certain other conditions is one thing, but establishing causality—or determining whether both are simply signs of a body compromised by general poor health—is another.
Oral Bacteria and Cardiovascular Disease
It is well established that oral infections can cause bloodstream infections. This is why patients with replacement heart valves have long received 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. Atherosclerosis is a condition where cholesterol, fat, and calcium build up into plaque on artery walls, restricting blood flow. This plaque is different from dental plaque, but both harden over time and are associated with inflammation. 'The majority of bacteria in atherosclerotic plaque is from the mouth,' says Kerrigan. Scientists are working to determine whether these oral bacteria enter the bloodstream and cause atherosclerosis, or whether the plaque is triggered by another mechanism but then attracts the bacteria. In either case, once the bacteria are present, they can increase inflammation and create other health problems.
Oral bacteria can also increase the risk of 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,' explains Kerrigan. Platelets normally help stop bleeding. '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. 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, it can cause a heart attack. When a clot forms on heart valves, it leads to infective endocarditis, preventing the valve from closing properly and potentially causing heart failure. 'These things are quite well recognised,' says Kerrigan, adding that nearly all of the bacteria found that trigger these clots are oral bacteria.
Diabetes and Oral Health
Diabetes is another condition with a well-established link to oral health. A 2025 study found that 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 additional heart health benefits. This suggests that removing damaged or infected pulp deep inside a tooth and sealing the roots could not only save the tooth but also help protect against type 2 diabetes. The diabetes connection is bidirectional: gum disease increases the risk of developing diabetes because systemic inflammation from oral infections can disrupt blood sugar control; conversely, poorly controlled diabetes makes one 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.
Dementia and Cognitive Decline
Correlations between oral health and dementia are also under investigation, although no causal link has been proven, says Jing Kang, senior lecturer in medical statistics at King's College London. There is a chicken-and-egg question: cognitive impairment can make it harder to maintain oral hygiene. A 2016 study by Kang's colleagues found that gum disease was associated with a six-fold increase in the rate of cognitive decline over six months. The study also found that gum disease was associated with a relative increase in the pro-inflammatory state, which makes the body more vulnerable to major illnesses, including cancers, neurodegenerative and metabolic diseases, and depression. One theoretical route, says Kang, is that 'it is all related to the immune response and inflammation.' However, pinpointing a precise causal mechanism is difficult, and there may be many factors. Behaviours such as food choices and lifestyle could impact oral health. Cardiovascular disease and chronic metabolic diseases associated with oral health could also affect brain degeneration. Poor education in childhood may lead to worsening oral health over time, and the resulting inflammation in later life could affect cognitive function. 'There are all sorts of hypotheses, but it's hard to prove and further studies are needed,' Kang says.
Kang suggests that gum pain could be a potential window into what is happening inside the body. She and her colleagues are working to establish whether treating oral health issues promptly could prevent or delay cognitive decline. They are only at the proof-of-concept stage, but she says it is never too late to take better care of our mouths.
Quality of Life and Arthritis
Advanced gum disease and tooth decay can be painful, smelly, and unsightly, affecting quality of life. 'Oral health is reflected in how we feel, our appearance, our confidence,' says Kang. People with gum disease are less confident and may avoid socialising, which can affect the brain and other parts of the body. Pain and inflammation may lead to increased medication use, and some medications have side effects that reduce saliva production, further harming oral health. 'So everything is interlinked,' she says.
According to Kang's research, brushing twice a day and flossing may even help with aching knees. People with arthritic knees were more likely to have gum disease, and vice versa. Those with more gum disease were diagnosed with arthritis or saw faster deterioration than those with healthy teeth. Kang emphasises that this is statistical evidence at the population level and does not apply directly to individuals. 'Don't worry too much that if you see blood when brushing, you're going to get dementia the next day. It is just a message to keep our teeth and gums healthy.'
Practical Advice
The government's last oral health survey in 2021 found that a quarter of adults with natural teeth reported damaged, cracked, or broken teeth, fillings, crowns, or bridges. However, accessing NHS emergency help or treatment is increasingly difficult, leading to reports of people self-treating or even pulling out their own teeth. Kerrigan notes that even if a tooth is professionally removed, most people cannot afford implants, so the mouth's microbiome changes. 'The bacteria in your mouth are critically important because they are the first step in digestion.'
To minimise risks, Kerrigan recommends brushing at least twice a day, morning and evening, and ideally also during the day. Electric toothbrushes with rotating heads are probably more effective at removing bacteria. Flossing and cleaning between teeth are also advised. Diet plays a crucial role: sugary snacks feed bacteria, so limiting sugar intake helps reduce bacterial damage to teeth and gums. However, Kerrigan cautions against focusing solely on oral health at the expense of other aspects of a healthy lifestyle. 'The person who runs several times a week probably has perfect oral hygiene as well. If you look after one part of your body, you tend to look after all parts.'
