The young woman hesitates, unsure, at the threshold of the doctor's office, hand covering her mouth. She is 30 years old, fits nicely into her size 10 dress and what is visible of her face is attractive. Nevertheless, every movement of her body signals insecurity and apology for her appearance. She slips into a chair and seems to shrink into herself.

Behind the hand are teeth that have changed this women's life, shaped her personality by marring her appearance and making it impossible for her to chew properly. Now, as she enters her 30s, she will wear braces.

At the climax of the "Me Decade," thousands of adults are breaking free of the old belief that braces are for kids.

"Braces are becoming badges of courage for adults," says Dr. Jeremy Orchin, whose D.C. practice includes 60 percent adults. "They're proud to be doing something about their problem."

A quick rundown on orthodontists' adult patients: a 6-foot-4, 250-pound U.S. marshal (who wears a .45 along with his braces), judges, professional singers, actors, actresses, and a trumpet player who wanted to be able to hit high "C".

D.C. Police Officer Bill Hinkle and his Pat have three children who are braceless; their parents both wear them. "They call me "tinsel mouth," says Hinkle, who teaches Traffic School. He adds, "I don't think I'd do it if I were a patrol officer."

To alleviate image problems like that, one orthodontist outfitted two FBI agents with removable braces; the agents had been told they could not wear any that showed while apprehending someone.

"I had the choice of wearing braces in my 30s or having false teeth in my 40s," says Vicki North, an associate manager of a Great Falls, Va., realty firm, whose three children also wear braces. "Everybody says, except for my wrinkles, I look 17 with my braces."

"Absolutely, we see differences that braces can make in adult lives," says Dr. Orchin. (One of his patients, a former nude dancer, "loves herself now" and has a new career in a bank.

"We see these shy, retiring people come in who don't want to smile, gradually change and get more courage," says Dr. Ashur Chavoor, former chairman of the Georgetown Department of Orthodontics and a pioneer in adult braces, whose practice now includes about 25 percent adults. "You almost want to consider how it will change their lives, but you can't."

One woman, a professor at the College of William & Mary, Williamsburg, and the patient of a Springfield orthodontist, got her braces at 64. She's now sailing around the world in a 60-foot sailing yacht with her new husband; her braces were taken off for the wedding.

"We are the pioneers," says Dr. Richard Saland, a dentist himself and a 35-year-old patient of New York orthodontist Dr. Marc Lenchen.

"I went to a party the other night and four of my friends were wearing braces. We're not embarrassed or apologetic. We put long-term benefits ahead of present comfort. That's the definition of an adult. Also, I had two canines that looked like shark teeth."

Although many orthodontists use plastic braces, many still prefer to work with metal because they get a better result in a shorter time. They find plastic braces tend to turn yellow and may break, requiring more office visits.

"Cosmetic dentistry is a wave of the future," says Dr. Michael McCombs, Vienna, president of the Fairfax County Dental Society." As technology develops, white braces (like the aluminum oxide used in spark plugs), as strong as the stainless steel now used will be available."

In some cases, the thin plastic -- and barely noticeable -- brackets bonded to the teeth are effective. One New York actress wore them -- without causing comment -- on the Broadway stage.

More and more orthodontists believe that braces may not only insure a healthy mouth, but can save plenty of dollars that otherwise might be spent on bridgework and crowns -- with the added advantage that adults end up with their own natural teeth.

Nationwide, the average price for restraining and realigning errant teeth by orthodontistry is $2,000.

Orthodonistry by mechanical means goes back to the mid-18th century, though treatment of tooth irregularities by finger pressure was advised by Celsus, who died in 50 A.D. Modern orthodontics first came into full flower after World War II, and even then was more or less limited to the children of the affluent in large cities. In 1946 there were about 1,500 orthodontists in the country; today there are more than five times that many.

More dentists and fewer children, plus the resolve of the 70s generation to be their own best friend, has raised the percentage of adults sitting in orthodontists' waiting rooms to between 10 and 20 percent. Patients are most apt to be women, and often married "I've got my man," as one said, "and now I can do this."

"Ten or 12 years ago we saw predominantly patients who had to have braces," says Dr. Mel Kogod, an instructor at Georgetown, whose private practice includes 20 to 25 percent adults. "More recently, adults are coming in for cosmetic reasons and appreciate the health reasons later."

Adults today are more apt to realize that out-of-line teeth get unusual stress and don't last as long as they should. Young professionals have more discretionary funds and want the best of what life offers. They don't want to compromise, or learn to chew only on one side. They want to eliminate things that give them grief and, along with the stereo and the car, they want a balanced bite.

The biggest hurdle for many adults who want to get their teeth straightened is sitting in the waiting room with the kids, filling out blanks that have lines for parental permission and school attended. If you're a trial lawyer and you have to wait side by side with a squirming 12-year-old, resolution and unassailable dignity are necessary. In some orthodontists' offices grown-ups get different forms and in some cases, semi-private areas.

Adults going into braces ask a lot of questions and some orthodontists find that a profile of the patient mounted with a hinged jaw helps explanations. Each tooth is a separate piece like bits of a jigsaw puzzle, and the result is a graphic demonstration of how things are now, and how they will change after treatment.

Overcrowding is a frequent reason for facial "disharmony," as the orthodontists call it, and the reason for the removal of a tooth is easy to see when it all takes place first on a mockup.

Some adults, even having gotten as far as the office, have lingering doubts about how braces will affect their lives. ("New, single patients," says one orthodontist, "always want to know how braces will affect their sex lives.")

Some orthodontists suggest easing into treatment, perhaps starting with one side only, realigning teeth that are out of sight. More than one actress began treatment this way.

So today's braces are not as noticeable. Do they still hurt?

"For the first week they feel like a tight pair of shoes you can't take off," says New York's Dr. Lemchen. But compensation for pain comes quicker than one might think. Though the full course of treatment is usually about two years, a noticeably improved smile is possible within six months.

"The rewards really come when the adults take their braces off and we see a beautiful, happy smile," says Dr. McCombs. He and others mentioned how close adult patients and their orthodontists became. (They see each other something like every three weeks for two years.)

Adult orthodontistry today is largely the province of young adults. Middle-aged patients have to be selected more carefully. There can be complications and the process is more difficult for those well along in life. A middle-aged adult might well have to wear a retainer every night the rest of his life.

But some are doing just that. A thin wire and some rubber bands in the mouth may seem a small price to pay for a healthy mouth and a better appearance, and an escape from the dental problems malocclusion can bring later.

One of Dr. Lenchen's patients, wearing his, appeared on the Johnny Carson show.

"I even wore my headgear to work," says Gail Gottesman, 33, a Springfield, Va., technical manager for a computer firm. "People made jokes about me 'taking off,' but I am a very disciplined person and I knew I could put up with anything temporarily. When the braces came off and I went to work that first day, almost no one knew what was different."

Plus, she savors the memory of being in labor for the birth of one of her two children and delighting the nurses as "the first woman to come in with braces on."