Question: I'm in my 30s and starting to notice some of my teeth are yellowing. Is this normal? What are safe ways to whiten? Is there anything that I can do to slow down the yellowing?

Answer: Natural teeth have a tendency to get darker as we get older. There are several more-or-less-effective over- the-counter tooth-whitening products and toothpastes available in drug stores and pharmacies that may be helpful in making your teeth lighter again.

The most effective and safest way, however, is to do this under the supervision of a dental professional, who can assess the reason for the darkening and select the most appropriate solution.

The teeth may be discolored with stains from tea, coffee, tobacco, red wine, etc., which can only be removed with special cleaning and polishing instruments, preferably by a dentist or dental hygienist. If that's the case, this cleaning should be done before any other tooth-whitening procedure.

Depending on the severity of the tooth discoloration, the dental professional may select from several whitening options, which are done either in the office or at home.

For home tooth-whitening, a "mold" (bleaching tray) is typically custom-fabricated to fit over your teeth, then filled with the whitening material and worn at home as instructed. There are some possible side effects, especially teeth becoming temporarily more sensitive (another reason to do this under supervision from a dental health-care provider).

You write that "some" of your teeth are getting darker. The whitening procedures mentioned above are helpful only for teeth that are mostly intact and without large fillings, crowns, or other restorations. Some of the filling materials may get darker over time, while others do not change at all. In general, they cannot be "bleached" or "whitened" like natural teeth and may need to be replaced. In addition, any tooth decay must be removed before starting any whitening procedure.

Markus B. Blatz

Markus B. Blatz, D.M.D., Ph.D., is a professor of restorative dentistry and chairman of the department of preventive and restorative sciences at the University of Pennsylvania, School of Dental Medicine.