Men with gum disease have a 63% higher risk of developing pancreatic cancer, according to US researchers.
Gum disease is widespread in the adult population
The Harvard-based study suggests mouth bacteria, and the body's attempt to fight them, may produce carcinogenic chemicals which trigger disease.
However, other experts say poor dental hygiene is unlikely to increase the risk of cancer, and that other factors are probably to blame.
The study appears in the journal of the National Cancer Institute.
It is estimated that the majority of the adult population have some degree of gum (periodontal) disease, ranging from very slight inflammation to infection that eats away at gum tissue and bone.
Several studies have suggested links between periodontal disease and illnesses including heart disease and diabetes.
However, the exact connection is unclear, particularly whether the mouth problem is causing the other problem, or whether something unrelated is causing both.
Smoking, for example, is the prime cause of both periodontal disease and numerous other serious illnesses.
The latest research was carried out at the Harvard School of Public Health and the Dana-Farber Cancer Institute, with experts looking at questionnaires filled in by more than 51,000 health professionals, and comparing these with their health.
A total of 216 cases of pancreatic cancer were confirmed in the study group, and of these, 67 had written that they had periodontal disease.
Even after this had been adjusted to take account of smoking habits, diabetes and weight, there still appeared to be an increased risk of pancreatic cancer.
Dominique Michaud, an assistant professor of epidemiology at Harvard School of Public Health, said: "Our study provides the first strong evidence that periodontal disease may increase the risk of pancreatic cancer.
"This finding is of significance as it may provide some new insights into the mechanism of this highly fatal disease."
The researchers suggested that the long-term inflammation associated with gum disease might release chemicals into the bloodstream that might help cancers grow - or that the bacterial film attacking the mouth might be producing cancer-promoting substances.
UK experts were quick to reassure members of the public that this did not provide proof that gum problems were causing dangerous diseases.
Professor Simon Langley-Evans, a nutrition researcher from the School of Biosciences at Nottingham University said that at most, having periodontal disease might be a "warning sign" that your lifestyle was increasing the risk of serious illness.
He said: "Almost everyone has some degree of periodontal disease - the problem with this kind of study is that not everyone will report that in a questionnaire.
"I think it may be a marker for the same kind of health behaviours - such as smoking - that drive pancreatic cancer."
Dr Philip Preshaw, who carries out research into periodontal disease at Newcastle University, was also cautious about drawing any firm conclusions from the study.
"Studies such as this one have been greeted with headlines like 'Floss or Die' - which is totally over the top.
"The trouble is that both periodontal disease and smoking tend to be under-reported in surveys, which means the study can be biased."
He said that while it was possible that the link proposed by the study authors existed, it was also possible that the extreme inflammation in severe periodontal disease might be a sign of an natural bodily overreaction that, when reproduced elsewhere in the body, might lead to other illnesses.
"We think there is a relationship between diabetes and periodontal disease," he said, "and this may be one of the reasons behind it."