Arm yourself to the teeth: choose tooth-friendly foods that leave behind marginal residue.

I grew up admiring sharks. As nature's most orthodontically blessed creatures, these benthic wonders can produce a treasure-trove of teeth; a single tiger shark, for instance, can manufacture 12,000 gleaming choppers in just five years.

Alas, our allotment wasn't quite as generous. But with devoted care, our compliment of 32 incisors, canines, bicuspids, and molars can provide a lifetime of service. The key is unflagging vigilance against tooth decay and gum disease. A simple formula, yet easier said than done.

At the root of our dental woes, both literally and figuratively, are bacteria. The human mouth is a veritable microbial Amazon. Bacteria feed on leftovers around our uppers and lowers, enveloping teeth in a sticky, acidic matrix known as plaque. Acidic plaque gnaws away at our teeth's protective enamel crowns, forming cavities. Left to fester, it corrodes the tooth's less-resilient interior, eventually requiring a major filling, root canal, or worse--extraction.

Time of the essence. It's not news that cavity formation is linked to dietary choices. But dental researchers now have irrefutable proof that even more influential a factor than any particular food's composition in sparking the onset of cavities is how long foods reside in die mouth. In other words, time is of the essence. The longer teeth and edibles especially carbohydrates) commingle, the longer the teeth are subjected to a deluge of enamel-hungry acids.

It stands to reason, then, says Carole Palmer, assistant professor of nutrition and preventive dentistry at Tufts University in Boston, that nursing three moderately sugary cups of a favorite beverage is significantly more perilous to oral health than knocking back a single super-sweet cup. Similarly, hard candies and cough drops rank among the most dangerous agents. Ditto for such obvious troublemakers as dried fruits and jelly beans, and starches like cookies, pastries, crackers, and potato chips. In fact, dentists now widely consider such starches to be even harder to wash away--and thus more troublesome--than truly sticky foods.

Snack attacks. Fortunately, some snacks are both healthful and tooth-friendly. Popcorn, nuts, plain yogurt, peanuts, and unsweetened peanut butter are among the best. Aged cheeses--cheddars, Swiss, gouda, among them--have the uncanny ability to retard cavity formation, especially around receding gumlines. Crunchy raw vegetables and fruits are tooth allies as well, helping to exercise the gums and invite saliva, which neutralizes bacterial acids and flushes food particles out of the mouth.

Anything that impairs the function of the salivary glands (the average battery of glands yields over a liter of saliva per day), including numerous medications, threatens dental fortitude. Palmer warns that reaching for slow-to-dissolve candy to alleviate a dry mouth may exacerbate the problem. Instead, she suggests drinking unsweetened beverages and chewing sugarless gum.

If timing is everything, or nearly so, what's a concerned tooth owner to do? First, cut down on between-meal snacking. Second, if you must snack, choose tooth-friendly foods that leave behind marginal residue. Third, if you indulge in decay-promoting foods, do so with meals, when salivary flow is at its zenith. Then brush and floss, because the truth is, no one has yet improved on brushing and flossing for maintaining healthy teeth and gums.

A thorough morning cleansing (at least three minutes) is especially crucial since diminished salivary function at night allows plaque to industriously colonize your mouth. (If you haven't received a lesson in self-care since grade school, have a dentist or hygienist instruct you on the current techniques.

Periodontitis. While cavities are blatant attention grabbers, gum disease--periodontitis--is insidious, quietly eroding the unseen bone, connective tissue, and gums supporting teeth below the gumline. Like decay, periodontitis is of bacterial origin; it is also oddly episodic and site specific, often afflicting a lone tooth while sparing its neighbors. Only after bacteria-filled pockets have undermined a tooth's scaffolding might you notice a loose tooth, change in bite, persistent bad breath, or pus that could indicate the disease's presence and warrant a trip to your dental practitioner. An estimated 10 to 20 percent of adults suffer from severe periodontal disease, many unawares.

If caught early, dentists can arrest periodontitis, but it's up to patients to prevent a relapse with conscientious home care. If the periodontitis is advanced, more invasive and expensive surgical treatment will be required to save the tooth.

How do you prevent periodontitis? Again, proper nutrition and rigorous hygiene are critical to refusing the culpable bacteria a foothold. Once bacteria become entrenched below the gumline, they are secure from any amount of brushing, flossing, and mouthwashing.

So arm yourself to the teeth with floss, brush, and prudent eating patterns. But remember: Although this arsenal constitutes the first and best line of self-defense against the bacteria that ferment cavities and periodontal hardships, they are only as effective as the person wielding them. Elbow grease, diligence, and dedication are the cornerstones of a successful campaign to keep your whites pearly and your gums healthy for years to come. sitting with small children while parents visit the sick one in the hospital, or assisting with errands and meals will be a step in the right direction. Others will heed the call to volunteer as an AIDS caregiver.

Most of us are able to donate blood. Donating blood is a perfectly safe way we can give of ourselves to help people with AIDS. Becoming involved in a local AIDS project or training as an AIDS hot line volunteer are other choices that will help us move from spectators to participants. Involvement will give us a form of knowledge far more valuable than statistics or medical facts: it will give us personal experience and empathy.

Few Are Flossing

We purchase toothpaste by the gallon every year but barely buy enough floss to string up a gnat. I fac, in 1992 we bought just enough to floss just once.

While Americans bought more than 14 million gallons of toothpaste that year, they bought just 59,000 miles of floss. That sounds like a lot of floss, but it works out to less than 12 inches per

Harvey A. Elder, M.D., is a professor of medicine at Loma Linda University School of Medicine and chief of infectious diseases at the Jerry L Pettis Veterans Administration Medical Center in Loma Linda, California. Cheri Lynn Gregory is an English teacher and writer who lives in Alta Loma, California, with her husband and two children.