Regulators eye link between denture cream and zinc toxicity

Regulators eye link between denture cream and zinc toxicity

Regulatory authorities and dental associations are examining reports that overuse of zinc-based denture adhesives may cause neurological damage. While a direct causal link has not yet been established, dentists are being advised to counsel denture-wearing patients to ensure they aren't using too much adhesive.

The issue has been percolating for several years, but received renewed attention this month following a segment that appeared May 5 on "Good Morning America." In addition, the U.S. FDA has received adverse event reports claiming that cases of zinc toxicity were caused by denture cream overuse, and the agency has confirmed that it has formed a working group to examine the issue.

At issue is the effect that excessive ingestion of zinc over a long period of time can have in depleting the amount of copper in the human body, as copper deficiency can lead to the impairment of various neurological processes. In fact, copper deficiency is a well-established and increasingly recognized cause of neurologic and hematologic disease, and excess zinc has been identified as a source of copper deficiency (Journal of Neurology, January 2004, Vol. 251:1, pp. 111-114).

This is where denture adhesives come in -- some, anyway. While not all denture creams contain zinc, two of the most popular are GlaxoSmithKline's (GSK) Super PoliGrip and Procter and Gamble's (P&G) Fixodent, both of which are zinc-based (GSK also offers a zinc-free version of PoliGrip). The zinc acts as a binding agent that increases the product's hold, according to Jennifer May, a spokesperson for over-the-counter products at GSK.

While zinc is an essential mineral naturally present in many protein-rich foods such as beef, chicken, and nuts, and many supplements and other over-the-counter products such as Zicam (a cold medicine), there are limits to how much a person should ingest on a daily basis, especially with long-term use. The acceptable daily intake is 8 mg for women and 11 mg for men, and more than 40 mg constitutes zinc poisoning, according to the U.S. National Academy of Sciences.

A 2.4 oz (68 gram) tube of Super PoliGrip contains 38 mg of zinc per gram of product, and GSK recommends that a single tube should last approximately six weeks. According to the company's Web site:

You should not use more than the indicated quantity of Super PoliGrip, or use it more often than once per day, to compensate for poorly fitting dentures. You should consult your dentist regularly to maintain proper-fitting dentures.

The Super PoliGrip packaging carries these same recommendations, along with the list of ingredients (topping the list is "poly(methylvinylether/maleic acid) sodium-magnesium-zinc mixed partial salt").

Language on the Fixodent packaging is less explicit; under "Helpful Hints," a highlighted section reads "Don't use too much product at first. It may take a few tries to find the right amount for you!" and "Consult your dentist regularly to ensure proper fitting dentures." There is no list of ingredients on either the Fixodent box or tube; because the FDA has classified denture cream as a Class I device, the manufacturers are not required to list the ingredients.

However, the Fixodent Web site does feature a letter from J. Leslie Winston, D.D.S., Ph.D., P&G's director of professional and scientific relations for North America, which states in part:

A small amount of zinc is used in Fixodent to provide denture hold. This helps the denture stay in place securely so our consumers can eat, chew, and talk more confidently. All Fixodent products undergo rigorous scientific evaluations and safety testing before appearing on shelf and we continue to monitor them once in market. ... The average amount of zinc an average denture adhesive user would ingest from daily usage of Fixodent is less than the amount of zinc in most daily multivitamins and comparable to 6 ounces of ground beef.