Losing your teeth is not an inevitable consequence of aging. It's caused by an insidious gum disease that can be prevented or successfully treated.

Yet nine out of 10 adult Americans have it.

It's called periodontitis -- a bacterial infection under the gums -- and it accounts for 70 percent of teeth lost after age 40. National Health Survey statistics show that 68 percent of teen-agers and 39 percent of children 6 to 11 have mild gingivitis (inflamed gums), the beginnings of disease, and a small number of this group even have infected pockets around the teeth.

"If you could start an educational program in the schools, not just brushing the surfaces of the teeth, but flossing between the teeth and below the gums with fluoride toothpaste to get rid of bacteria, and then motivate young people to do it, you could prevent periodontitis altogether," said Dr. Micah Krichevsky, research microbiologist at the National Institute of Dental Research (NIDR).

Ten years ago, people with gum disease either let their teeth fall out one by one or tried to arrest the process with surgery.

Now research findings challenge the traditional view that surgery is the only way to treat this tricky disease. A number of studies have shown that a relatively inexpensive nonsurgical approach, based on killing the harmful bacteria with antibacterial agents will allow the body to heal itself.

Dr. Paul H. Keyes, a dental researcher for 27 years at NIDR and now chairman of the International Dental Health Foundation (IDHF) in Reston, said his treatment tightens loose teeth, shrinks pockets and helps the body replace lost bone.

Keyes' method does not rule out surgery. Stubborn cases that refuse to respond after a year may require surgery, Keyes said. Dr. Dan L. Watt, Keyes' associate at IDHF, estimates that 90 percent of surgery done today is not necessary. Studies in the United States and Sweden have shown nonsurgical treatment to be at least as effective as surgery.

The daily routine a patient follows at home is simple. It involves using an antibacterial agent -- a mix of baking soda and hydrogen peroxide, fluoride toothpaste or the twice as active fluoride gel -- with a toothbrush or rubber-tipped applicator, or irrigating with an antibacterial solution such as saturated salt water. These are applied under the margins of the gums. Keyes and Watt usually recommend the soda, salt and peroxide because they are less expensive. Watt cautions that most of the new "anti-plaque" toothpastes on the market are not antibacterial; they remove bacteria by abrasion, which may damage the tooth surface, he said.

Professional care in a dentist's office where the Keyes technique is used differs from usual treatment in three ways:Diagnosis includes a microscopic examination of the oral cavity flora (added to the usual exam for bleeding, pus, loose teeth, swelling of the tissues, inflammation and malocclusion). Regular monitoring assesses changes in the population of microorganisms under the gums and the prevalence of white blood cells. Treatment is adjusted to suit a patient's progress. For example, infection-fighting agents can be applied with a rubber-tipped applicator, water pic, syringe or irrigation device, and systemic antibiotics, such as tetracycline, may be added to overcome resistant bacteria or inaccessible infections.

Even advocates of surgery believe that surgery is a last-resort treatment for periodontitis. Dr. Sheldon Holen, dental researcher at Georgetown University Medical and Dental schools, and a periodontist who treats 80 patients a week, said that surgery is needed only when the pocket is inaccessible. By cleaning out these caches, surgery helps to stop destruction of bone and to regenerate bone and attachment fibers, if this is possible.

Holen characterizes himself as both conservative and aggressive. He believes in stopping short of surgery if the initial treatment -- scaling, root planing and bite adjustment of mobile teeth -- works. On the other hand, he'll go further to save a loose tooth that others might extract.

Holen said that "surgery is expensive absolutely, but not relatively, when you consider that a crown on a front tooth now costs about $475. The average fee for surgery on four quadrants is $2,500," he said, "but surgery represents an advanced case. Periodontal treatment could be thought of as costing in the hundreds."

Treatment alternatives and cost aside, not everyone can be treated by a periodontist. There are only 3,000 to 4,000 specialists in the country, and 94 million people with some degree of gum disease.

The answer, said Holen, is to prevent the disease and to seek good primary care. The American Association of Public Health Dentists (AAPHD) sees the general dentist as the "pivotal" element in the prevention and treatment of periodontal problems, but the dental hygienist is the "critical" element. In North Carolina, for example, the AAPHD reports, general dentists spend less than 2 percent of their time on periodontal disease.

Some of the differences among treatment approaches for periodontitis come from the professional's understanding of the periodontal disease process and microbiology.

Watt, for instance, if faced with recurring infectious episodes, would suggest that the patient's spouse come in for treatment as well, because he considers the infection contagious. Kissing can be hazardous. After a New Year's Eve party, Watt said, he does a meticulous cleaning job to wipe out acquired invaders.

Holen believes that by the time you reach adulthood all the bacteria that are going to set up housekeeping have already done so. "The bacteria did come from direct contact, but early in life, not later on. People who live together for 20 years do not have bacteria similar to a mate anywhere -- the tongue, teeth or crevices. Don't worry about kissing. I'm all for kissing."

Confidence in antibacterial agents is another point of conflict among periodontists. Holen said "there is not one iota of evidence that you can sterilize the mouth by eliminating all bad bacteria ." He dismisses claims about the wonders of salt. "I see no reason to use salt. There is no evidence that salt or baking soda, which was a 19th-century dentifrice, is any better or worse than toothpaste. Fluoride toothpaste may have a little antibacterial activity."

Holen also believes the water pic is ineffective. "The bacteria are sandwiched in between two layers of sticky protein. The salt and water pass over quickly and do not remove the bacteria. It's like washing grease off a pot."

Holen outlined what he considers a typical approach periodontists use with prospective patients: "If you've had no clinical experience, we would tell you that we'd put you through preliminary treatment and then see if you need surgery. That's what we say to people, and sometimes we say that because we don't want to frighten them.

"You get benefit from preliminary treatment such as scaling, root planing, bite adjustment of mobile teeth, and antibiotics even if you don't need surgery. If the treatment is working, that's all the treatment you get, but you get a lot of it."

Holen has decided not to do surgery if a person has not followed through on good home care. "I've done surgery on one half of a mouth and wouldn't do it on the other half because it would have been useless. Instead, we have people with poor home care come in every six weeks for gradual curettage scraping of the pocket walls . This patient will get some benefit, although he'll be slipping gradually over the years."

With surgery, Holen can "reduce the pocket" that shelters the bacteria. "Within two, three or five years you'll have a moderate pocket again," he explains. "It's a chronic condition. You never discharge a patient in some sense."

When the condition flares up again, the crevices deepen and the tissues swell. That's when Holen asks his patients to "work hard." He puts them on tetracycline "to knock out the bad actors" and schedules more frequent office visits. "You want to avoid slipping back to where you'll need more surgery," he said.

Home care is at the heart of the matter. "In a consensus meeting at the National Institutes of Health ," the NIDR's Krichevsky said, "one study showed much improvement in attachment loss after surgery. But buried in the statement on a five-year follow-up is the sentence: 'Rejected from the study were patients who after one year showed evidence of poor home care.' They weren't counted. Periodontists all agree that if you don't do good home care, surgery is ineffective."

Periodontal disease is a complicated business, said Krichevsky. The main problem is "we don't know enough to make judgment on which techniques are better. We can't as yet measure what we are treating."

The nature of the disease is part of the problem. Periodontitis is a chronic, but not continuously progressive, ailment. It ranges from mild to serious at different times and even in different parts of an individual's mouth. It also is sneaky. It is painless in the early stages, so often is ignored until bone loss shows up on X-rays. The gums may be pink and firm on top while underneath the bacteria are multiplying. Eventually, red, inflamed gums give away the clandestine parasites.

In different phases of the disease, the bacterial population expands and contracts irregularly for complex reasons that may include stress, which affects the immunological defense system. In a way, it's like fighting guerrillas in jungle warfare. No one can predict when or where they are going to attack next.

Although the consensus now is that scaling and root planing done about every three months is the most effective counterattack, regular checkups of the bacterial population are not always helpful. With a disease that comes and goes, "it doesn't do any good to check for bacteria in a person's mouth. The disease may last only a few days and then stop," said Krichevsky.

"Maybe you get damage out of that particular incident and maybe you don't," he said. "Another incident may come along at a later date and if you examine that person in between times, you are not going to see anything.

"I'm convinced," said Krichevsky, "that if you clean up the bacteria in people's pockets in general, you're going to get an improvement. I don't think there's any question that Keyes' patients at NIH did improve. That's not controversial."

Krichevsky would choose the conservative treatment route at the start. "If it doesn't work, you can always have surgery. There's no statistical evidence that surgery works either. These patients have relapses, too."

Krichevsky keeps his own gums in condition by brushing with a fluoride toothpaste, leaving some in his mouth and then flossing to force the paste under the gums.

Even with the best-designed study and the most effective treatment, concludes Krichevsky, individual motivation will still determine the results. "I don't know if anyone has a design for motivating people. It's a difficult thing, because the periodontal regime is tough. Who wants to do this stuff every single day? Patients who do succeed are highly motivated.

"Barbara McGarry Peters is a consultant at the World Bank.