Americans reportedly drop $1.4 billion annually on nonprescription teeth whitening products to bleach away the effects of cigarettes, coffee, red wine, or just plain age. Certain medications, notably tetracycline, also discolor teeth, says Gennaro Cataldo, a Henry M. Goldman School of Dental Medicine professor of general dentistry.

But is the bite to your wallet worth it?

The government doesn’t regulate whiteners, warns Cataldo, and “many of them are ineffective.” On the other hand, some do work.

To what degree is losing that pearly white shine unavoidable and natural?

Cataldo: Almost universally, teeth will get darker with age. For most older people, their teeth will turn kind of a brownish yellow—not necessarily from smoking, from coffee, or wine. Our hair turns white, and our teeth turn yellow. I wish it were the other way around. Other teeth turn out to be grayish. There’s a whole spectrum of what is normal.

Whatever the cause, are over-the-counter products effective?

There are two types of discoloration: intrinsic, the one that develops with time and is the natural color. Then there’s extrinsic color due to deposits on the teeth from smoking or coffee or other materials or due to medication taken by the patient—or by the mother when the patient was in utero. We also have patients who just don’t take good care of their teeth.

Bleach will not work with a stain from major deposits caused because a patient has not brushed their teeth. If we’re not taking care of our teeth, we’re not going to get a very effective whitening from any type of product. The teeth have to be in a healthy condition; if a patient hasn’t been to the dentist for a while and if there are any cavities or decay going on and the whitening material gets within that cavity, it can cause excruciating pain.

So we have to start with teeth, gums, a patient who is healthy. Then, over-the-counter whitening agents can work effectively. But because it’s not dentist-monitored, many of them don’t do anything. For instance, a mouthwash containing a whitening agent such as hydrogen peroxide probably is not going to be very effective. There are some products that use a light that we flash on our teeth to accelerate whitening. Even the whitening lights that we use in the dental office are no more effective than other ways of whitening teeth.

If you want white teeth, dentists have tried-and-true methods. Some allow us just to paint on a whitening solution to sit on the teeth a half hour, 45 minutes in the dental office. Totally different from the material you buy in the drugstore. It’s highly concentrated; the gums actually have to be protected from this material.

Are there any over-the-counter products that you would recommend?

Crest Whitestrips work. There are trays which are purchased in the pharmacy, put into water and heated, and placed into the mouth to mold the tray to the patient’s mouth. Then whitening agent is put in. Those work. I said mouthwashes wouldn’t whiten your teeth, but if you’re going to be rinsing six to nine times a day and holding it in your mouth for a couple of minutes, and you’re going to do this for two or three months, we’d probably see a whitening occur. Look at the label—they’ll have some type of peroxide.

But there is no guidance by a dentist to monitor all this. Are the gums becoming irritated? Is the patient overdoing it? Are there cavities that are going to get sensitive because of this material? Will the teeth become as white as what is done in the dental office? Probably not as rapidly. It might take two or three months with over-the-counter products, whereas when we use products that can only be purchased in a dental office, those are going to work within three or four days to a week or so.

Does dental insurance cover teeth whitening?

Mostly not. That’s a cosmetic procedure.

How often should a person whiten his or her teeth?

I can speak to the products we use in the office: when we whiten, usually it will last about two years. I generally recommend patients touch up that bleaching every time they have a cleaning on a six-month basis.

The recommended procedure, and least expensive, is a home bleaching procedure. The dentist takes an impression of the patient’s mouth and from that impression makes a whitening tray. It fits in the patient’s mouth like a mouth guard. Whitening material can be placed inside in a gel form. Some people wear them overnight, while they’re sleeping; other patients wear them during the day because they’re virtually invisible. This is meant to be worn for an hour or two, once a day. It’s plus or minus $500.

I think any over-the-counter product can be harmful, because it can be easily misused or overused. As a matter of fact, whitening materials in the dental office, over a prolonged period of time, could probably do harm. We don’t know for certain. We have had patients come in who had a burn mark on their gums because they’ve overdone it. This is all reversible harm, but we’ve had patients for whom we have gone through the home bleaching, they did the right thing, and they called a day or two later in excruciating pain. They were sensitive to the material. They could still bleach; we had to adjust the concentration and how the tray was fitted to their mouth.

Bottom line: if you want to whiten, you should consult your dentist first, and even then, beware that whitening can have problems?

Whitening in general can have problems. It’s very rare. But this is what dentist-monitored whitening is about, to make sure that you’re doing it effectively.