When Bob Zebrowski graduated from the Georgetown University School of Dentistry last May, he had been working nights and weekends as a grocery checkout clerk in the Georgetown Safeway for three years.

He still is. His plastic Safeway name plate reads "Bob Z., DDS."

One of his supervisors added the DDS to Zebrowski's name tag last summer as a joke.

"I said, 'I'm not gonna wear that,' " Zebrowski recalls. "Then I thought, 'Yeah, I'm gonna wear that.' "

Somewhere between the first thought and the second, Zebrowski probably remembered that Northwest Washington, where he was about to go into practice, has about four times as many dentists per capita as the national average. It may also have occurred to him that he was nearly $50,000 in debt from dental school.

Shoppers at Safeway notice the DDS in the name tag, he says. "They look at it. You can tell they're looking at it."

Some customers ask about it; most don't. But if they do, Zebrowski has a wad of business cards for his Connecticut Avenue practice ready in his wallet.

Dentistry today faces a disconcerting dare: Can it put itself out of business? The unlikely challenge is rooted in the irony that tooth decay, the most widespread illness in America except the common cold, is now almost wholly preventable.

"For the first time in the history of man, we are now experiencing a substantial decrease in the prevalence of dental caries decay ," says Harald Lo e, director of the National Institute of Dental Research.

Dental health has come a long way since World War II, when about 200,000 recruits were rejected from the armed forces because they had fewer than 12 solid teeth out of a possible 32.

In the last decade, tooth decay in children under 18 has been halved. In the latest federal health survey, one of three children had no cavities. Fluoridation, tooth-protecting plastic sealants, better nutrition and improved home care -- let alone new-frontier technologies such as a decay-fighting vaccine and genetic engineering -- offer hope for a cavity-free society by the end of the century.

That's good for children, but a mixed blessing for some dentists. Dental progress, combined with an oversupply of dentists in some areas, has created what is euphemistically known in the trade as "the busyness problem."

"They finish four years of school," says Robert Beck, president of the Hamilton Group Inc., a computer company whose customers include a lot of dentists. "They're called a doctor. They walk out into the world.

"And nobody wants them."

"Here is a way to fill your most costly cavity -- your empty chair," claims a recruitment advertisement by Insurance Dentists of America (IDOA), a national group of dentists who provide care at set fees for employes covered by several large insurance companies.

One of the hottest seminars at dental conventions these days is likely to be titled "Coping With the Busyness Problem" or "Developing Patient Load." A dental meeting in New York last month offered seminars not only on such technical topics as occlusal splints and subperiosteal implants but also on "Listening -- the Key to Productivity," "Managing Stress," "Marketing Your Image" and "Where Did My Practice Go -- and How Do I Get It Back?"

In a field that career counselors used to label "can't-miss," competition is growing. "Retail" dental centers are springing up in shopping malls, under such signs as Sears, Sterling and Zayre.

Pressure from cost-conscious employers, unions and government has spawned an acronymic array of so-called alternative delivery systems -- health maintenance organizations (HMOs), independent practice associations (IPAs), preferred provider organizations (PPOs) -- that further threaten to make the traditional solo-practice family dentist the exception rather than the rule.

Increasing competition has driven many dentists to overcome their traditional aversion to advertising and, in some cases, to adopt marketing techniques worthy of a toothpaste-selling conglomerate. In many dental offices today, the computer is as vital a tool as the high-speed drill.

"It's very difficult for a young dentist out of school," says Norman Ressin, a College Park dentist. "You used to be able to sit back and wait for the patients to come in. You can't do that anymore.

"What happens is, you finally get some patients to come in, and they don't have much work to be done."

The sardonic joke among dentists, he says, is that dentistry "will be one of the first professions to literally put itself out of business.

"We're much ahead of our brothers in medicine. We've been preaching prevention for years and years."

A decade ago it would have been unthinkable:

A dental center in a renovated department store in Dearborn, Mich., has 46 dental chairs and 250 employes -- including 40 dentists working in two shifts -- and sees up to 400 patients a day.

The center is the largest in a chain of eight in Michigan and New Jersey. Under contracts with Ford Motor Co., Chrysler Corp. and other big companies, it provides dental care at a fixed monthly fee per employe, whether or not the employe seeks care.

"We see the market expanding from the well-to-do, I-can-afford-it patient of 10 years ago, down to middle America," says Joel Sharenow, chief operating officer for the chain, Eastern and Midwestern Dental Centers, which leaped onto the Inc. magazine list of 500 fastest-growing companies last year.

Noting that half the population does not see a dentist regularly, Sharenow says, "How would you like to go into business knowing you had a potential market like that out there?

"But you've got to go out and get them. Marketing is no longer a dirty word."

Marketing was a dirty word back for dentists back in 1963, when Arthur Alexander graduated from dental school at the Medical College of Virginia and, like most of his classmates, went into private practice. He moved to Alexandria and, without knowing a soul there, opened an office that he was confident would set him up for life.

In 1963, expectations were high for a graduating dentist. "We knew of nobody who was unsuccessful," he recalls. "You opened a practice and the patients came.

"It was solid."

For Alexander and most dentists of his generation, private-practice dentistry offered the dual appeal of a sure-fire livelihood and independence. It would be just like medicine, but without the hassles and the night work.

It's different today. Fewer than 20 percent of the graduates of Georgetown's dental school start their own practices upon graduation. The rest specialize, enter the military, join an established practice or take a salaried job with a dental center or franchise.

Many dentists of an earlier generation are concerned about their profession -- not so much because they abhor advertising (though many do), or because they oppose prepayment plans (though many do), or because they think "retail dentistry" is a contradiction in terms (though many do), but because they fear a loss of cherished independence.

"When I graduated 30 years ago, I could have gone to almost any community and started a practice and had a full practice within a year," says Stanley Hazen, dean of the Georgetown School of Dentistry. "Today, a lot of areas have too many dentists."

In the early 1970s, the federal government began pumping subsidies into the nation's dental schools to boost enrollment to meet a perceived shortage of dentists. The plan worked -- and it didn't. It has enlarged the nation's supply of dentists to more than 125,000. But half the population still stays away, while the swelling ranks of dentists compete for business from the other half.

As the projected shortage gave way to a projected glut, the federal government cut back on funding, and many dental schools reduced their admissions. Enrollment, which peaked in 1978, has fallen by about 20 percent at the nation's 60 dental schools, says Errol Reese, dean of the University of Maryland Dental School.

Reese says fears of a glut are unfounded. Never has dentistry been so exciting, he says, with all the space-age materials and technologies available and whole new fields emerging, such as periodontics (treatment of gum disease) and cosmetic dentistry. He's puzzled by the shrinking pool of applicants to dental school.

"For the first time in our history," Reese says, "we have to spend a tremendous amount of time and energy attracting people to a profession that's both high-tech and high-touch, that will put them in at least the top 4 percent of all wage earners and that, almost without question, has success written all over the DDS degree."

The market for dentistry remains vast, and dentists aren't likely to go the way of the blacksmith. Americans spent $20 billion on dental care in 1982. Dental insurance, still growing, now covers about 100 million Americans.

The average dentist netted more than $56,000 in 1982, according to a survey by the American Dental Association (ADA).

But in places like metropolitan Washington, competition among dentists has never been keener. As of 1982, the nation averaged about one professionally active dentist for every 1,889 people. In the District, there was one per 992 residents, a higher concentration than in any state.

In Northwest Washington, the concentration is even higher, about four times the national average. And the highly mobile population -- about 20 percent of Washington residents move in a given year -- heightens the scramble for patients.

"We have to get 20 percent new patients in our practice every year just to stand still," says Jerold Frankel, who shares a practice in Northwest Washington.

"I know an awful lot of dentists in their fifties who never dreamed it would be like this and who are really bitter," Frankel says. "It's like someone promised them a rose garden and took it away."

Frankel and his partner, Robert Eisenberg, advertise heavily in the Yellow Pages, in newspapers, on television and on Metrobuses. Last month they sent out a mass mailing of brochures to 85,000 potential customers in the metropolitan area.

"The game," says Frankel, "has changed completely."

Until a few years ago, the closest a dentist came to advertising was a telephone listing in the Yellow Pages. Today, the Yellow Pages are jammed with quarter- and half-page ads for dentists seeking a marketing edge. They pitch corny slogans ("Take the bite out of your dental bill," "North or south, take care of your mouth"), convenience ("near Metro"), evening and weekend hours, senior citizen discounts, credit cards and foreign languages ("On parle franc,ais," "Se habla espan ol").

But even today, seven years after the Supreme Court cleared the way for dentists and other professionals to advertise, there is widespread ethical opposition to advertising, particularly among older dentists. When the American Dental Association last year proposed buying prime television time for ads featuring James Whitmore urging viewers to see a dentist regularly, the ADA House of Delegates voted the idea down. (Another factor was fear that the ads would raise ADA dues.)

But the ADA has enlisted the help of "Sesame Street" star Kermit the Frog to promote next month as National Children's Health Month. Kermit, in a Sherlock Holmes outfit, is cast as a Tooth SLEUTH (Start Learning to End Unhealthy Tooth Habits).

Some dentists prefer to emphasize "internal marketing," a computer-age term for tender loving care. They promote "needleless" ways of minimizing pain and anxiety, such as hypnosis, stereo headsets, nitrous oxide ("like a good martini without the hangover," says one dentist), or tropical fish.

Fish? "To reduce the anxiety level of patients," says Alexander, who just installed a fish tank in his office. "Patients love it. I get patients who cluster by the tank. "We have to rotate the chairs in the waiting room, because the ones next to the tank wear down faster." "Internal marketing" also means follow-up phone calls to patients after major treatments. Or flower arrangements for patients who are in the hospital maternity ward.

Norman Ressin and his College Park partner, Walter Miller, hold a Halloween party for their patients every year.

"They love it," says Miller. "Some patients schedule a year ahead of time just to be there that day.

"This year I was a clown. Last year I was a tin man. The year before that I was the scariest Dracula you've ever seen."

Every health profession should be working itself out of existence," says Peter Tsaknis, professor of dentistry at Howard University College of Dentistry. "We're not there yet, and we probably never will be, but we're working in the right direction."

The whole emphasis of dentistry has changed, he says, from the old standby of "drill-and-fill" to prevention of cavities and gum disease, from extracting teeth to saving them.

As dental decay becomes less rampant, dentists are focusing more on periodontal (gum) disease, which can lead to loosening or loss of teeth.

Gum disease is especially insidious because it's painless in early stages. Up to 75 percent of Americans have some degree of periodontal disease, but most don't know it.

"So we have less cavities," says private practitioner Alexander. "Great! But wear and tear is a function of living, and the more teeth we retain, the more potential for other problems to develop.

"You don't do a root canal on a tooth that's been extracted and is sitting in a glass jar."

Dentistry has always been a business. But today the stakes are higher, the pace of change quicker, the competition keener.

"Twenty years ago," says Richard Crowse, a Frederick dentist and past president of the Maryland Dental Association, "a dentist could succeed even if he paid little attention to the business aspects of the job. Today that's impossible."

The typical dental school graduate owes about $20,000 by graduation, and the average debt for graduates of a private school such as Georgetown is closer to $40,000.

To open a private practice in an urban area is prohibitively expensive for most graduates today. Just renovating and equipping an office costs more than $100,000.

"A dental office is kind of like a miniature outpatient hospital," says Maryland's Reese. "A dentist is a trained practitioner, but he also has to be a manager of people, a manager of property, a manager of money and a manager of accounts receivable like you wouldn't believe."

"I never wanted to become a businessman," says Alan Marx, whose dental office is near Dupont Circle. "All I wanted to do was technical dentistry. Now I'm making business decisions I never had to make before. In dental school, they give you an idea of [how to organize a practice], but it doesn't scratch the surface of what you're dealing with.

"How do you get a new patient? I still don't know."

The challenge of dentistry, for Marx and his colleagues, is still to combine sound business practices with technical skill and a caring approach to patients. Even in an era of newfangled prepayment plans and computerized claims, many dentists are finding that TLC may be their best marketing tool.

"Life has really become automated," Marx says. "But in dentistry, we don't deal with inanimate objects. We're dealing with human beings.

"We're dealing with nerves."