Parents faced with the hair-tearing task of instilling in their children the importance of regular toothbrushing could probably do with a house call from Dr Efthymios Deliargyris. Where previously they would have had to resort to dark mutterings about the perils of dental neglect - scare tactics along the lines of "all your teeth will fall out" - Deliargyris, a cardiologist at the University of North Carolina, has come up with a rather more convincing threat. According to a study he presented to the American Heart Association's annual meeting at the weekend, gum disease could be a significant contributory factor in a large proportion of heart attacks.
The most common afflictions always seem the most baffling to medical researchers: just look at the common cold. In the case of heart attacks, one third of all instances of the country's biggest killer remain unexplained by the conventional risk factors of high blood pressure, high cholesterol, diabetes and smoking.
Deliargyris may be edging towards a solution to the mystery. In his study, periodontal disease - the official term for advanced gum disease, as opposed to the less serious gingivitis - was found in 85% of subjects who had suffered heart attacks, compared with 29% of those who had not. The 85% in question also displayed abnormally high levels in their bloodstream of a protein, CRP, which is associated with both conditions.
Alarming stuff. And yet the finding is only a small part of a growing body of evidence suggesting that this most common of ailments - gum disease affects around 10% of the population to a serious degree, and many others less acutely - could be implicated in a wide range of conditions, from pneumonia to premature birth.
The mouth is awash with bacteria at the best of times, but most of them are beneficial. Problems only arise when destructive bacteria - plaque - are allowed to build up, leading to sore and bleeding gums, bad breath and loose teeth. Swollen and torn gums provide the bacteria with an easy entry point into the bloodstream, where they can trigger an inflammatory response in the arteries associated with heart attacks.
"The one thing we know about [gum disease and heart attacks] is that they tend to initiate an immune response, also called an inflammatory response, in the body. We believe that patients with a heart attack and periodontal disease have an exaggerated inflammatory response . . . that might put them at risk of future heart attacks," says Deliargyris, whose findings have particular significance for those who have already suffered a heart attack and want to reduce the risk of a repeat occurrence. "This work also raises the possibility that by treating severe gum disease in people with heart attacks, we might be able to reduce their CRP levels and their risk of another heart attack."
To probe the links between the mouth and the heart is to enter the murky world of epidemiological correlation - where the prevalence of one condition in a population suffering from another cannot be taken as proof of causation, and few experts are willing to say for certain what they think is going on. But the evidence, in study after study, is growing more convincing. One such investigation found that gum disease was a stronger predictor of heart disease in the American subject group than any of the conventional risk factors.
"We know that bacteria get from the mouth to the bloodstream very regularly - if you have a tooth extracted, for example, it will happen to a minor degree," says Newell Johnson, professor of oral medicine and pathology at King's College, London. "Most people clear it from their bloodstream quickly, but if you have advanced periodontal disease, you already have a deep-seated infection in pockets around the teeth."
Once the plaque bacteria have entered the bloodstream, it may not just be coronary problems that ensue. A study published in September found that women with severe gum disease were more than seven times more likely to give birth to a premature, low-weight baby than those with healthy gums, possibly because the bacteria in plaque can have an inflammatory effect on the placenta. "The results of the trial indicate that the effect of gum disease in pregnancy seems to be as harmful as other well-established risk factors such as smoking," the report's author, Professor Steven Offenbacher, said at the time.
Dental professionals are understandably unwilling to say so, but overvigorous flossing or brushing can also contribute to the problem once gum disease has taken hold, further damaging tissue in the mouth and sending more bacteria into the bloodstream. But it's not that simple, of course: underzealous brushing is one of the surest ways to contract the disease in the first place. Another is a deficiency in levels of saliva, which contains antibodies that fight infection: a dry mouth - brought on, for example, by many prescription drugs - can increase the risk of gum disease considerably.
There are those who dispute the link entirely. Two months ago, the world's medical media fixated briefly on a study from the University of Washington suggesting that there was no clear connection between gum disease and heart attacks - or if there was, it was "very small or very hard to reliably detect", according to Philippe Hujoel, the lead researcher. (Critics of the study, including Johnson, point to the historical data on gum disease on which it relied, collected at a time when the measurement of the prevalence of diseases in the population was still in a fairly primitive state.)
Even if gum disease correlates strongly with a range of health problems, a significant part of the explanation may be due to other causes with social roots. "People who neglect their health neglect other parts of their bodies as well, so we have to be careful," says Robin Seymour, of Newcastle University's dental school, who has conducted research into the links between gum disease and heart attacks. Nevertheless, he adds, "With heart disease the evidence shows a strong association. And it appears to be like a dose response: the worse the gum disease, the greater the risk of coronary heart disease.
"What we still haven't established, though, is the impact of intervention: whether, if you treat gum disease successfully, you actually reduce the risk of coronary events." While the jury is out, the British Heart Foundation recommends that anybody with a heart condition should take particularly good care of their mouth and teeth: the same advice, of course, that we have all been receiving since we were toddlers - only this time with an even better incentive for compliance.