(MONEY Magazine) – America has discovered a new fountain of youth: that gurgling, stainless-steel spittoon just to the left of your dentist's chair. In their quest for more gorgeous grins, Americans endured some 45 million cosmetic dental procedures in 1990, according to a once-a-decade survey of dentists taken by the American Dental Association. Moreover, say many dentists, cosmetic procedures have done nothing but grow in popularity since then. For example, a poll of 376 dentists taken by the Smile Design Council, a New York City association of cosmetic dentists, reported a tenfold increase in just one cosmetic procedure, tooth bleaching, over the past three years.

These days, in fact, even elaborate treatments that were once mainly the province of the Hollywood set are trickling down to Main Street. Example: porcelain veneers, in which thin sheets of the ceramic are glued over teeth to whiten them and fill gaps. Price: $600 to $1,200 per tooth for effects that can last a decade or so. "Five years ago, porcelain veneers were still thought of as something just movie stars did," says Los Angeles dentist Dr. Christine Dumas, who is also a consumer adviser to the ADA. "Now they've become very commonplace."

Interested? For prices ranging from a few hundred to a few thousand dollars -- covered by dental insurance only if the procedure is needed to restore normal tooth function -- you can get a smile worth at least a Warholian 15 minutes of fame. We say: Sandra Bullock, watch out! On the other hand, if you're thinking of buying a grin like hers or, say, Brad Pitt's, you need to watch out. While cosmetic dentistry could be in your practitioner's best interest, it may not be in yours -- medically or monetarily.

First, a quick background. The economics of dentistry are undergoing some profound changes. Americans' dental health has improved dramatically since 1945, the year the cavity-fighter fluoride was first added to local water supplies. That change has meant that many dentists have seen a 15% to 40% falloff in the traditional drill-and-fill side of their businesses. "If dentistry were an airline," says Donald Mayes, a dentist and dental-benefits consultant in Hershey, Pa., "it would be flying at only 65% capacity." Thus to plug the gaps (so to speak) in their practices, more and more dentists have been promoting cosmetic improvements -- and finding plenty of eager customers. Yet Dr. Mayes, among other authorities, maintains there is a lot of "unnecessary crowning, bonding and bleaching," including some shoddy work that, he says, actually leaves patients worse off.

So if you are pondering a mouth makeover, you can save some grief and possibly some teeth by taking these precautions:

-- SHOP AROUND. If your dentist suggests cosmetic work, get a second opinion and maybe even a third. Some dentists offer free consultations, while others charge up to $75. If a fee is involved, ask whether it will be applied to the dental work if you decide to proceed.

-- STUDY THE PHOTOGRAPHIC EVIDENCE. Don't settle for just a couple of before-and-after photos showing the dentist's very best work, says Dr. Scott Coleman, a Houston dentist. His advice: Ask to see 50 or more sets. That should give you a sense of the dentist's average work. A dentist with computer-imaging equipment can also give you an idea of what your remodeled mouth might look like.

-- LISTEN UP. Ask the dentist to explain the procedures available to you, as well as the risks and possible pain associated with each treatment. While cosmetic dentistry is generally less invasive than conventional dentistry, you can still experience discomfort, such as a sore jaw from having your mouth propped open for hours at a time.

-- TAKE IT SLOW. Your dentist may propose a combination of treatments -- veneers, bleaching, bonding, crowns -- depending on the look you want. "Go for the most conservative, least invasive option first," advises Dr. Dumas. That means, for example, go for tooth whitening or bonding (in which custom-blended resins are used to fill gaps and chips) before insisting on porcelain veneers.

Still ready for a smile makeover? Sink your teeth into this list of the latest dental beauty treatments, then make sure you can swallow what they are likely to cost you.

BLEACHING. Far and away today's cheapest and most popular cosmetic dentistry procedure, bleaching doesn't require any filing or removal of tooth structure. Patients have three choices: in-office bleaching, take-home bleaching prescribed by dentists, and over-the-counter whitening products.

In-office or "power" bleaching is the strongest, quickest and longest-lasting way to lighten teeth. Using a small brush, the dentist applies a high concentration of an active agent, usually a 30% to 35% solution of hydrogen peroxide, then uses heat or light to activate the chemical process. A rubber dam keeps the bleaching agent from coming in contact with gums and mucous membranes. The treatment generally requires two to four sessions at $200 to $500 a pop -- more if teeth are badly stained -- and the effects typically last three to five years, depending on the foods you eat, whether you smoke, and how porous your tooth enamel is.

In take-home bleaching, the dentist creates custom-fitted carrier trays, which the patient fills with a prescribed cleaning gel and wears while sleeping, for up to two weeks. "It's generally cheaper for the patient [$350 to $800 for the full mouth], and they get a great result," Dr. Coleman says.

Take-home bleaching gels contain 10% to 15% carbamide peroxide, an active ingredient also used to clean wounds. Dr. Jeff Golub-Evans, a dentist and the chairman of the Smile Design Council, says that some patients complain of temporary discomfort after the procedure, principally from the bleaching agent coming in contact with gums, but so far no one has reported serious oral damage.

Over-the-counter whiteners contain a lower concentration of their active ingredient. But according to the ADA, which understandably prefers procedures prescribed by dentists, the over-the-counter agents can still cause damage to the tooth pulp, enamel, gums or other areas of the mouth.

PORCELAIN VENEERS. These are thin shells of porcelain laminate material fabricated in a lab from a dental impression of the patient's teeth. The veneers attach directly to the teeth and can be used to fill gaps between teeth as well as to cover teeth that are stained, poorly shaped, or crooked. "It's instant orthodontics for people who want an immediate fix from a cosmetic standpoint," says Dr. Ronald Feinman of Atlanta.

And nowadays they get just that. New processes allow dentists to apply porcelain veneers in as little as one day, compared with a week or more in the 1980s. "We've got the technology to a point where the patient can come in at seven in the morning for some impressions, come back at three or four and go home looking great by six," Dr. Coleman says. And while porcelain veneers require some filing down of the existing teeth to keep the veneered teeth from looking too thick, they represent a much less invasive procedure than caps or crowns, where the existing tooth is ground to a stump.

BONDING. In bonding, composite resins are blended to match the color of your teeth, then applied to repair discolorations, chips, breaks, cracks and gaps between them. "You use bonding to 'tweak' a smile, where one tooth is crooked or a space needs filling -- not to redo the entire mouth," says Dr. Coleman. No filing is required, just a bit of surface roughening with a solution that helps the bonding material adhere. At about $350 to $600 per tooth, bonding also costs less than porcelain veneers. Porcelain veneers are more durable, however, and bonding resins will discolor over time.

ORTHODONTICS. Today's new orthodontic appliances are far less conspicuous than the set-off-the-metal-detector hardware of yesteryear. Patients' options now include tooth-colored brackets and "invisible" braces that attach to the back of the teeth. Dr. Jeffrey Dorfman of New York City says that 90% of his orthodontic patients are adults. Two-thirds of them wear fixed braces; the rest, removable ones. "A lot of people in the public eye choose removables," says Dr. Dorfman. Removable braces must be worn 23 hours a day during the three to nine months that teeth take to move into their new positions. But once the teeth have been pulled into place, the braces need be worn only at night, usually for six to 18 months. A removable appliance can cost as little as $1,000.

Fixed braces for the full mouth run up to $5,000 -- a cost that is often partly offset by insurance. "Orthodontics is considered primarily functional" by insurers, says Dr. Dorfman, who reports that his patients typically have 50% coverage up to a total of $3,000. "Cosmetics is a secondary benefit." But insured or not, in a time when so many people want to be all they can pretend to be, orthodontics and other cosmetic cure-alls seem sure to spread faster than a salesman's smile.