Bad gums are linked to health problems
Gum disease, both in smokers and non-smokers, may be a warning sign of an increased risk of cancer.
Imperial College London researchers found gum disease was linked to a higher chance of lung, kidney, pancreatic and blood cancers.
Writing in Lancet Oncology, the team, who studied the health records of 50,000 men, said an immune system weakness could cause both illnesses.
The British Dental Association stressed the need for regular check-ups.
The majority of Britons are said to suffer from some sort of gum disease, caused by a persistent bacterial infection, and the problem is more common in people who smoke.
However, the latest research suggests that, even in those who have never smoked, the presence of gum disease means a bigger risk of cancer.
The Imperial College team analysed questionnaires and health information provided by US men from 1986 onwards.
They found that those with a history of gum disease had a 14% higher chance of cancer compared with those with no history of gum disease.
There was a third increase in the risk of lung cancer, almost a 50% rise in the chance of kidney cancer, and a similar rise in pancreatic cancer.
Blood cell cancers such as leukaemia rose by 30% among men with gum disease.
While there was no rise in lung cancer chances among those with gum disease who had never smoked, there was a slightly higher increase in the overall risk of any cancer, and a similar rise in the rate of blood cancers.
There are a number of theories as to why the presence of gum disease might be linked to other illnesses.
People with gum infections have been found to have chemical signs that the inflammation there may be mirrored in other parts of the body - there have also been suggestions that bacteria linked to gum disease could cause problems elsewhere.
The researchers, led by Dr Dominique Michaud, said that the increase in blood cancers pointed to an immune system link.
They suggested that the persistent presence of gum disease might be a sign of weakness in the immune system which could also allow cancer to develop.
"These findings might represent a commonality in the immune function and response to inflammation, which results in susceptibility to both periodontal disease and haematological cancers."
However, they said it was also possible that long-lasting gum disease could trigger changes in the immune response which helped cancer thrive, or that the bacteria from the gum could be directly causing the cancer in the tissues of mouth or throat when swallowed.
However, they stopped short of saying that people with the problem should seek medical, rather than dental, help.
"At this point, we feel that any recommendations for prevention of cancer based on these findings are premature; patients with periodontal diseases should seek care from their dentists irrespective of the effect on cancer."
A spokesman for the British Dental Association said that while dentists were trained to spot cancers in the mouth, they were becoming increasingly aware of the implications of gum disease for overall health, and were prepared to refer patients on in cases of unexpectedly serious gum disease in otherwise healthy patients.
He said: "The first thing to remember is that gum disease can be treated and prevented.
"We should really be encouraging people to visit their dentist frequently, although many people do have trouble finding an NHS dentist.
"Dentists are health professionals, and are trained to recognise situations where patients may need additional help."
Dr Philip Preshaw, a senior lecturer in Periodontology at Newcastle University, said that the small increases in risk recorded by the study were not proof of a link.
"You are trying to look at the impact of a chronic disease over many years - it is very difficult to adjust for the effects of lifestyle over that period.
"I don't think there is any other convincing evidence for this."