An advertising campaign that says the mouthwash Listerine is as effective as floss at fighting tooth and gum decay is false and misleading and poses a public health risk, a judge has ruled.

U.S. District Judge Denny Chin said in a decision made public Friday that he will order Pfizer, the maker of Listerine, to stop the advertising campaign. The lawsuit was brought by a Johnson & Johnson company that makes dental floss.

“Dentists and hygienists have been telling their patients for decades to floss daily,” Chin wrote. “They have been doing so for good reason. The benefits of flossing are real — they are not a ‘myth.’ Pfizer’s implicit message that Listerine can replace floss is false and misleading.”

The judge ruled after McNeil-PPC Inc., a Johnson & Johnson subsidiary, filed a lawsuit saying that false claims in the advertising campaign that began last June posed an unfair threat against its sales of dental floss.

Flossing reduces tooth decay

Pfizer in print ads had featured a Listerine bottle balanced equally on a scale opposite a floss container with the words: “Listerine antiseptic is clinically proven to be as effective as floss at reducing plaque and gingivitis between the teeth.”

The campaign also featured a television commercial titled the “Big Bang.” In it, the commercial announces that Listerine is as effective as floss and that clinical tests prove it, though it does add that there is no replacement for flossing.

The judge said “substantial evidence” demonstrates that flossing is important in reducing tooth decay and gum disease and that it cannot be replaced by rinsing with a mouthwash.

The judge also noted that the authors of articles on which Pfizer based its ad campaign had emphasized that dental professionals should continue to recommend daily flossing and cautioned that they were not suggesting that mouthrinse be used instead of floss.

Messages left with Pfizer and McNeil-PPC on Friday were not immediately returned.