BECAUSE he wanted his breath to be closeup-fresh for working with patients, the Virginia optometrist had for many years used a mouthwash spray that contained sugar. Finally, when the man sought help, his teeth had eroded to stubs.

Instead of dentures--which at first seemed his only option--the optometrist now has a perfect set of teeth through a combination of capping and tooth bonding. The hefty price tag, $25,000, included traveling expenses between Washington and Manhattan, where the work was done by dental aesthetics pioneer Dr. Irwin Smigel (known to some as the James Bond of bonding).

The optometrist's case is, of course, an extreme one. Tooth bonding--although an increasingly popular choice--is still infrequently used in total mouth constructions and more often in simpler situations like filling front cavities, repairing chipped front teeth or filling spaces between teeth. Cases that dentists wouldn't touch before, such as the otherwise healthy, tetracycline-stained teeth of young adults, can now be treated by bonding.

Although the idea of bonding itself is not new, the techniques and materials have been improved greatly in recent years.

"With the possible exception of the X-ray machine," claims Smigel, "nothing has affected the profession the way bonding has. The main reason is, for the first time we can actually make people look better and be healthier without attacking the teeth."

Bonding eliminates grinding down intact, healthy parts of a tooth to form a point where the crown, or "cap," is cemented on like a jacket. Because it eliminates the need for a technician to make the crown and takes less time, a tooth can be bonded in a single visit--compared with a minimum of two for a crown--and costs one-half to a third of a crown.

Although situations vary, the cost of one cap in the D.C. area is about $300 and up; the cost of one entire-surface bonding, about $180 and up. Manhattan dentist Smigel puts the national range of caps at $300 to $1,200 each; bonding that covers the tooth, $150 to $500 each.

So why not bond every tooth that needs repair? For back teeth, the composite filling used in bonding is just not strong enough to hold up under the pressure of daily chewing. Researchers, however, are working on strengthening the material.

"By 1990," Smigel predicts, "people will not have to walk around with gold or silver on their back teeth. When they laugh, you won't see any metal."

Others, such as Bethesda prosthodontist Stuart Lane, view the bonding technique less dramatically. "It's terrific, it's been a boon to dentists, but it's not totally replacing the crowns of the future.

"Bonding," says Lane, "is indicated only in certain types of instances where there's a minor amount of tooth structure that is discolored or missing, for certain types of fillings and for replacing little corners that have chipped off. It's used for very conservative situations where you have to have something done quickly.

"For long-term aesthetics, you get much better aesthetics with a crown than with a bonded veneer."

IN BONDING, also called the acid-etch technique, the dentist paints the enamel surface of the tooth with a small amount of acid. Then the surface is painted with a resin, over which a composite resin (containing glass, quartz or ceramic) is painted. The resin locks into the etched areas on the tooth.

Some composites harden chemically in two or three minutes, not allowing the dentist much time to do his handiwork. With light-hardening composites, the dentist can shape and contour the filling, and when he has it just the way he wants it, he turns on a special bonding light.

"You see," says Smigel, who is president of the American Society for Dental Aesthetics, "it allows me to be an artist."

With the zeal of a true believer, Smigel has lectured on bonding all over the world for the last seven years. They used to laugh at him, he says, and now it's hard to find a seat at one of his lectures.

A number of dentists, however, don't go along with the excitement about the technique. "This is nothing more," says Potomac dentist J. Frederick Thornett, "than an extension of what every dentist has been doing--filling front teeth with white material--and everyone is making it up to be a specialty."

Everett Wolfe, acting chairman of Georgetown University's operative dentistry department, says the school's approach to bonding is a conservative one. "Like anything else," he says, "you've got to give it time and let it prove itself." At Georgetown, it's "one tooth here, one tooth there."

Says another Washington dentist, "Old habits die hard. There are still a lot of people out there who are not affiliated with dental schools, who don't have access to new materials and the discussions that go with them. They stay with things they are comfortable with and that aren't going to come back to haunt them in their practice."

Because the composite resin now in use bonds only to enamel, the technique does not work for people who lack enamel on their teeth. To solve that problem, R.L. Bowen, associate director of the American Dental Association Health Foundation's research unit at the National Bureau of Standards, Gaithersburg, has developed a bonding technique that works on both enamel and the underlying dentin.

The material is currently being used to fill monkeys' teeth, and if all goes well, Bowen expects it to be available in about two years. The new bonding material, says Bowen, should also reduce the amount of tooth that needs to be cut away to retain a filling.

Another offshoot of bonding is an appliance called the Maryland bridge. Developed by researchers at the University of Maryland, it eliminates the need for drilling down teeth adjacent to the missing tooth and capping them, with the false tooth attached in between. Instead, two metal wings on either side of the porcelain false tooth are bonded to the back of the adjacent teeth, which are otherwise untouched.

FOR PERSONS with gum disease, there is no need to recommend against either bonding or capping, says Washington periodontist Garry Miller. In fact, he says, "We use caps splinted together to help support the teeth. The bonding, however, would not be strong enough to facilitate this on a long-term basis, though we have used it to splint the teeth temporarily."

One disadvantage to bonded restorations cited by the American Dental Association: Life expectancy is only about five years. (Crowns last at least seven to 10 years.) And the association warns that in bonding it may be difficult to get an exact color match.

Louis LaVecchia, who has a private dental practice and also teaches at Georgetown, tells his patients that bonding lasts only two to five years. But most dental work wears out eventually, he added.

The technology, says LaVecchia, is improving daily. Staining has become less of a problem with newer materials. As for color, any time you try to match a bonded surface with the remaining tooth structure and the other teeth, it's "a challenge." But, he says, "There's enough available to play with to the point where we can match it adequately."

Paul Keyes, 66, the controversial baking-soda-and-peroxide-treatment guru now retired from the National Institute of Dental Research, had two front teeth--damaged in a childhood accident--coated with the bonding material 10 years ago. The result, he pronounces, is "excellent."

Meanwhile, the optometrist is ecstatic. "People marvel at my teeth. Oh my God, it's worth double the price. The alternative is to end up with dentures."

When people compliment him on his teeth, "I thank them. I don't go into any detail. As far as they are concerned, these are my teeth and I like to keep my little secret."