Cigarette smoking may play a major role in more than half of the cases of severe gum disease in adults nationwide, suggesting that one of the main causes of tooth loss could be prevented, a government study shows.

While it has long been known that smoking can help cause gum disease, this is the first national study to show how widespread the problem is, said Dr. Scott Tomar, a researcher with the federal Centers for Disease Control and Prevention.

Current smokers were about four times more likely than people who never smoked to have periodontitis, but ex-smokers who had abstained for 11 years faced no increased risk, according to Tomar, whose findings were published in the May issue of the Journal of Periodontology. Overall, 52.8 percent of periodontitis in the study was attributed to current and former smoking.

Periodontitis, advanced gum disease that destroys the tissue and bone surrounding the teeth, is generally caused by bacteria contained in plaque buildup.