For many people, a wide-open grin can become a self-conscious greeting fraught with embarrassment because of discolored or graying teeth. But there is a solution for troublesome tooth stains: whitening treatments available now through dental offices and drugstores. Treatments include in-office bleaching sessions, at-home dentist-supervised treatments, and over-the-counter products. Always see a dentist before doing any teeth-whitening procedure (discolored teeth can be a sign of cavities or infection). Here's a look at some of the more popular at-home treatments. None are permanent solutions, but some can last as long as six months before you have to re-treat your teeth.

These at-home whitening kits cost from approximately $15 to $45, and are aimed at removing long-term stains from coffee, smoking, and even just discoloration from aging. Most of these systems come with mouth trays that you fill with a bleaching solution, then apply to the upper and lower teeth for anywhere from 5 to 30 minutes, depending on the manufacturer's instructions. Most products claim that you will see results in a week, but often a two-week course of treatment, once or twice a day, is recommended. Instead of using mouth trays, some products are applied either by special applicator (Colgate Simply White is one example) or by toothbrush (Supersmile Professional Whitening System). Products like Crest Whitestrips adhere directly to the upper and lower teeth.

Most of these paste products contain polishing or chemical agents that remove surface stains on teeth, and they work better on minor staining and discoloration. A few, such as Rembrandt Dazzling White Toothpaste, Arm & Hammer Advance White Baking Soda and Peroxide Tartar Control, and Mentadent Fluoride Toothpaste with Baking Soda and Peroxide, contain a bleaching agent as well. The prices per tube or pump vary from approximately $3 to $10. Some people shouldn't try whitening at all, says Wynn Okuda, D.M.D., president of the American Academy of Cosmetic Dentistry. Avoid whitening agents if you have:

• Very severe dental stains
• Congenital discoloration
• Stains from drugs, such as tetracycline
• Cosmetic work, such as caps, crowns or veneers. These were designed to match your existing tooth color and won't get brighter from whitening treatments.
• Sensitive teeth: Bleaching agents will only make your teeth more sensitive.
• Finally, most whitening agents are not recommended for children under age 13.