Persistent consumer complaints are causing some stains on a Procter && Gamble Co. Crest product's reputation.

Crest Pro-Health Rinse hit the market three years ago as an alcohol-free mouthwash that not only freshens breath but fights oral maladies such as gingivitis and plaque. The strong-selling product has caused some users to report discoloration of their teeth and numbing taste.

P&G said "99.99 percent" of users have had no complaints and that any discoloration or aftertaste is temporary.

But a federal lawsuit alleging fraud in a proposed class action is pending in Georgia and the U.S. Food and Drug Administration, which approved the product, is gathering more information on complaints. The developments were first reported Wednesday by NBC's "Today" show.

Laura Brinker, a Crest spokeswoman, declined to comment on the pending litigation. She said the product is in full compliance with current standards.

A frequently-asked-question section on Crest's Web site addresses the question "Does Crest Pro-Health Rinse stain teeth brown?":

"Like all mouthwashes that effectively fight plaque and gingivitis, Crest Pro-Health Rinse can contribute to temporary, surface-level brown tooth discoloration, which is reported by a small percentage of individuals."

Dr. Robert Gerlach, who is identified on Crest's site as a dentist who also works for Crest and conducts clinical research on the rinse, defends the product.

"I want to assure you that Crest Pro-Health Rinse is safe and effective: the millions of consumers who use it every day, and the growing number of dentists who recommend it, can attest to that," Gerlach said on the site. "We perform extensive scientific and safety testing on all of our products and their ingredients before they are marketed, and continue to monitor them once in market. Crest Pro-Health Rinse's active ingredient has been recognized as safe and effective by an FDA advisory panel, and the label meets current FDA standards."

The Web site also notes that the product does not include any warning labels about staining or taste loss because the active ingredient in the rinse has been recognized as safe and effective by the FDA and that the label meets current FDA standards.

Crest also invited any consumers with additional concerns to contact the company's consumer relations department at 1-866-695-1856.

Additional Resource:

• Crest Web site