Newly publicized clinical research carrying the imprimatur of the American Dental Association (ADA) shows that rinsing twice daily with Listerine does "at least as good" a job of reducing gingivitis (swollen, irritated gums) and plaque (bacteria and the sticky stuff they feed on that cause gingivitis) as once-daily flossing.

So is it time for slaves to dental hygiene to throw off their floss? Can two 30-second rinses with the tingly elixir really replace the nightly ritual of winding the twin digital tourniquets, spattering the mirror with bits of dinner and drawing blood between those two unruly molars?

Of course not. If that were true, you'd have found out about it by now, via the tickertape parades in major cities, the mass dental floss bonfires and stadium-filling thanksgiving services.

Still, the research is tantalizing, especially to the estimated 85 to 90 percent of Americans who, according to dentist and ADA spokesman Matt Messina, fail to floss regularly.

The story begins with a study that was funded by Pfizer Consumer Healthcare, maker of Listerine, and published last year in the ADA's journal.

The study showed that, among 600 people ages 18 to 65 who had mild to moderate gingivitis, Listerine Antiseptic mouth rinse (civilians call it mouthwash) used as directed (twice-daily, 30-second rinses) reduced plaque between the teeth by 20 percent and gingivitis by 11.1 percent after six months.

Flossing, by contrast, reduced between-teeth plaque by only 3.4 percent and gingivitis by 4.3 percent in the same period.

The study confirmed the findings of earlier research, also funded by Pfizer, published in 2002 in the American Journal of Dentistry. Both studies apply to all versions of Listerine mouth rinse except the natural citrus variety.

Both Pfizer and the ADA emphasize that the results relate only to people with gingivitis, a mild form of gum disease that affects a majority of Americans over 30. Those with periodontitis, a more serious condition in which bacteria have affected the bony structure of the mouth, have no choice but to floss if they wish to be well.

From these two studies, published in respected, peer-reviewed journals, a reasonable person might infer that it's time to pitch the floss. But of course that's not the message the ADA -- or, for that matter, Pfizer -- wants you glean. And with good reason.

The ADA has for decades recommended twice-daily brushing and daily flossing, along with regular visits to the dentist.

That stance is reinforced by yet another Pfizer-sponsored study, this one published in the April 2004 issue of the ADA journal, which demonstrates that brushing plus flossing plus two Listerine rinses a day deliver the biggest anti-gingivitis punch of all.

Those in the study who merely brushed saw little change in the amount of plaque between their teeth or the degree of gingivitis they suffered at six months. Those who brushed and flossed reduced plaque by 8.9 percent and gingivitis by 7.7 percent during that time. Those who brushed, flossed and rinsed with Listerine saw a 52.4 percent reduction in plaque vs. the brushing-only group and a 22.3 percent reduction in gingivitis vs. the brushing-only group; the triple-treatment group's plaque reduction was 47.7 percent better and its gingivitis reduction 15.8 percent better than those of the brushing-and-flossing group.

Naresh Sharma of Bio-Sci Research Canada Ltd., a research laboratory that conducted the first and most recent studies for Pfizer, speculates that brushing and flossing not only scrape away most of the plaque (thus reducing the ranks of bacteria to be reckoned with) but also help disrupt the surface of any remaining plaque, creating opportunities for the Listerine to get at more of the bacteria.

In the new study, patients in the brushing-only group and in the brushing-and-flossing contingent both used mouth rinse that didn't contain Listerine's essential oils, just to make sure that it was the ingredients in Listerine, not the mechanical action of liquid swishing over teeth, that improved outcomes.

In the mid-1980s, Listerine became one of the first mouth rinses to receive the ADA's "seal of acceptance" for its role in reducing plaque and gingivitis. Research supporting that distinction showed that Listerine's four active ingredients -- the essential oils thymol, eucalyptol, methyl salicylate and menthol -- were effective in reducing plaque and thus limiting its assault on the gums. Now any private-label and store-brand Listerine look-alike can make the same claims, provided it has Listerine's exact mix of active ingredients.

(Alcohol, which accounts for up to 26.9 percent of Listerine's volume, is listed as an inactive ingredient. Last decade's scary stories linking Listerine's alcohol to oral cancer risk have been largely discounted.)

The results of the 2002 and 2003 studies have been in dental professionals' hands for some time. You're just hearing about them now because of the vagaries of ADA protocol: Products such as Listerine that wish to publicize research-based claims must first have those claims reviewed by the ADA's Council on Scientific Affairs. Cliff Whall, a leading member of that council, explains that it was only in March that Pfizer won permission from the ADA to publicize Listerine's effectiveness relative to dental floss.

The 2004 study hasn't yet been reviewed by the council, Whall says, so while your dentist may have read it and may be figuring out how to deliver the news to patients, you're not really supposed to know about it yet.

"The ADA's position still is clear," Whall said. "Brush two times a day with a fluoride dentifrice, floss every day to remove plaque. But we also recognize that this company [Pfizer] has done two studies [not counting the 2004 one] that satisfy our criteria" for establishing that essential-oil-containing mouth rinse is as good as flossing at combating plaque and gingivitis.

Which puts you in a funny position. On the one hand, the compelling data from the 2003 study might support your tendency to go floss-free. But now that we've told you about the newer study, which shows that Listerine is even more effective when added to a flossing regimen, you can't pretend not to know better.

Dentist Messina, who practices near Cleveland, is in the same boat. "I'm afraid people will make too big a jump" and give up flossing altogether, he said. "I'm not willing to let go of something I know works really well [brushing and flossing] for something we believe may be a good adjunct [adding mouth rinse to the mix]."

Messina concedes that while brushing, flossing and rinsing remains the best approach against gingivitis, "if we have only time to just brush and rinse, that's better than not doing anything."

Is that permission to ditch the floss? At least once in a while?

You didn't hear it from us.

*

Jennifer Huget, a regular contributor to Health, wrote about a new approach to understanding religion in last week's issue.