Millions of Americans may soon take a pill to help fight advanced gum disease. It won't replace that painful scraping away of hardened plaque patients now endure at the dentist's office, but the newly approved drug can make their gums significantly healthier.

CollaGenex Pharmaceuticals' Periostat is a new way to treat gum disease. Until now, treatments have focused just on attacking the bacteria that cause periodontal disease.Periostat, by contrast, suppresses an enzyme found in inflamed gums that literally breaks down the gums and eventually the bones that hold teeth in place. So Periostat, when used after dentists scrape away hardened bacteria, can slow, or perhaps even halt, the progression of gum disease.

"This is a whole new concept," said Dr. Sebastian Ciancio, who studied Periostat at the State University of New York, Buffalo. "For the first time, we have a drug that helps the body begin to heal."

Using Periostat daily, "it looks like we've arrested the disease in cases where patients were told by their dentists that they were probably going to lose their teeth," added Dr. Lorne Golub of SUNY's Stony Brook campus, who discovered the enzyme's role in research that led to Periostat.

CollaGenex announced the Food and Drug Administration's approval of Periostat on Thursday, saying the prescription-only pill will be on pharmacy shelves within two months. A price has not been finalized, but a spokeswoman said treatment would cost between $1 and $4 a day.

One study found that patients who took Periostat daily after dentists scraped away plaque had their gums reattach to teeth 52 percent better than patients who had plaque removal alone. Perio-stat patients also had 67 percent more improvement in the depth of gum loss.

Half of Americans have gingivitis, a gum inflammation often controlled with proper brushing and flossing. But in at least 20 million Americans, the problem advances to serious periodontal disease in which gums pull away from the root of teeth and underlying bone is destroyed.

Dentists use special instruments to regularly scrape off plaque, sticky bacteria, that hardens below the gum's surface, a painful procedure called "scaling and planing." Dentists also prescribe topical antibiotics. Still, some patients need extensive gum surgery and lose teeth.

Golub discovered, somewhat accidentally, that attacking the bacteria alone isn't the whole answer. He was studying why diabetics have higher rates of gum disease when he discovered that spraying antibiotics onto the gums of rats didn't just attack germs - it also suppressed the enzyme collagenase. That substance destroys gum tissue.

Wondering if that was just an extra effect of antibiotics or clinically important, Golub studied specially bred, germ-free rats - so rare they cost $70 each - and found that suppressing collagenase was a new and separate way to attack gum disease.

A weakened form of the antibiotic doxycycline, so weak that it doesn't attack bacteria but does target collagenase, seemed to work best. CollaGenex named the pill Periostat and studied it in 800 patients.

One, Jo Ann Buczkowski of North Tonawanda, N.Y., said the pill has made her regular plaque scalings require less time - and cause less pain. "I used to do a lot of bleeding before and I get very little bleeding now," she said.

The American Dental Association greeted the pill "with guarded optimism," said Dr. Dan Myer, its associate scientific director.

Dentists want more detailed studies of the drug's long-term effects, and patients still must properly brush and fight gum-attacking bacteria, he stressed. But Periostat "does have the promise of slowing down the disease."

Nobody knows how long patients should take Periostat, something scientists continue to study.