Doctors say too much zinc drives down copper levels in the body. This sets up a chain reaction that affects the spinal cord and makes it hard to walk and maintain balance. Nardin said, "Small amounts of denture cream are certainly safe for people. It's people whose dentures are ill-fitting, who are using excessive amounts ... who are at risk of running into trouble with zinc toxicity."
The authors of a 2008 study published in the Journal of Neurology theorize that long-term denture cream overuse was the culprit in the cases of four patients who had unexplained limb weakness and poor balance. Dr. Sharon Nations, who led the study, is an associate professor in the department of neurology at the University of Texas Southwestern Medical Center. "The patients were using at least two tubes of denture cream a week. ... So, it was long exposure to very high amounts of denture cream that led to their problem."
The FDA does not require that manufacturers list the amount of zinc, so the researchers tested the products themselves. The zinc varied from 17 to 34 milligrams per gram of denture cream. Significant amounts, according to the researchers. Dr. Jaya Trivedi, also an associate professor in University of Texas Southwestern Medical Center's neurology department, said, "If you have poorly fitting dentures, then seek professional help. Go and see your dentist, because we don't want them to be using large amounts of denture cream to keep the dentures in place." The researchers said more study is needed.
But it is unclear how many denture wearers understand the potential risks if they don't follow these recommendations -- especially those who suffer from ill-fitting dentures who are more likely to use greater amounts of denture cream. In fact, in the last few years, several denture wearers have filed lawsuits against GSK and P&G claiming that the companies' zinc-based denture adhesives have resulted in serious disabilities.
At this point, 17 actions have been filed in the U.S., according to Eric Chaffin, an attorney with Bernstein Liebhard in New York City who has so far filed five cases for five individuals, four against GSK in state court in Philadelphia and one against both GSK and P&G in federal court.
"In many of these cases, the description is that the plaintiffs use 'excessive amounts' of denture cream," Chaffin said. "But there is no clear indication from the manufacturers on how much is too much. 'Do not use more than once a day without consulting your dentist' is incidental to the directions and does not warn consumers about potential zinc poisoning or copper deficiency."
But in court papers obtained by "ABC News," GSK and P&G said there is no scientific proof that denture cream can cause zinc-related illnesses. In previously issued statements, GSK has stated that "the vast majority of the zinc in the product remains in the adhesive and is not released into the mouth. Thus the potential for absorption of zinc through the gums is minimal."
The best advice: If you have ill-fitting dentures, see your dentist for a reline. Avoid excess use of denture creams.