The study, published in the Journal of the American Medical Association, found marijuana was responsible for one-third of the new cases of periodontal disease in adults ages 26 and 32 who smoked marijuana more than 40 times a year.

W. Murray Thomson of the school of dentistry at The University of Otago, New Zealand, measured gum recession at three sites on each tooth at ages 26 and again at 32 in study tracking nearly 1,000 people born in Dunedin, New Zealand, in 1972 and 1973.

The link between gum disease and marijuana emerged from a statistical analysis that controlled for gender, dental care, socio-economic status and how clean or dirty the teeth were.

Most of the self-identified heavy marijuana users said they were also smokers of tobacco but the smoking factor was controlled statistically. The researchers also found a link between marijuana use and gum disease in the non-smokers.

"Heavy cannabis (marijuana) use has been linked to greater risks of developing respiratory disease and some psychiatric conditions," Terrie Moffitt, a Duke University professor who participated in the study. "Gum disease should be added to that list of known hazards."