There's no doubt that a smile can light up your face. However, if you've noticed your smile isn't as bright as it used to be, there are many products and lifestyle strategies that can help. We asked Van B. Haywood DMD, professor in the Oral Rehabilitation department at Georgia Health Sciences University's College of Dental Medicine, for the facts about what impacts the color of teeth -- and what are the best, safest ways to remove stains and give you the most dazzling smile possible.

What discolors teeth?

If your teeth seemed a lot whiter when you were a youngster, you aren't imagining it. Teeth tend to become more yellow as we grow older. "It's a natural consequence of aging because, over the years, more tooth structure is laid down on the inside of the tooth (the dentin) and it is yellow," Dr. Haywood explains.

Some people are simply born with yellow teeth, or single dark teeth, much like eye color or hair color. In those cases, Dr. Haywood days, only bleaching will help.

Some medications can also change tooth color. "Minocycline, the number one drug used for acne, causes both teeth and bone to turn slightly gray over time. Other drugs or water containing high amounts of iron or fluoride can also stain teeth. In fact, some areas with high mineral content in the water have an entire community with stained teeth."

What we eat and drink, especially in excess, can contribute to a not-so-pretty discoloration of teeth, too. Coffee is a well-known tooth staining substance, but there are plenty of others, including many berry juices and red wine. "Also, drinking too many acidic drinks (including fruit juices, cola drinks, and wines) can erode enamel away and cause the teeth to look more yellow, since the color of the tooth comes from the inside," Dr. Haywood explains. "Cake icing with red food coloring can contribute to stains, as well."

The worst cause of all, he adds, is something that's totally avoidable -- nicotine stains on teeth from smoking. Dr. Haywood also points out a little known risk to your smile that can result from simply swimming a lot. It turns out that chlorine from pool water can erode tooth enamel. So consider wearing a mouth guard to protect your teeth if you are an avid swimmer.

Some things you put in your mouth can actually help keep your smile brighter. Dr. Haywood notes. For example, chewing gum can stimulate saliva flow, helping to keep teeth cleaner. However, to be smile-friendly, the gum you chose should be sugarless.

Are there any foods that can help keep your smile bright? Munching on crunchy natural snacks like apples, celery, and carrots are good choices. "Probably anything that has roughage, like an apple, is helpful to remove plaque, which tends to stain and look dark," Dr. Haywood tells us.

Brush to brighten

Can simple good dental hygiene -- brushing and flossing multiple times a day, and regular dental cleanings -- go a long way to keep teeth white? "Yes, for the most part. But surprisingly, even people who feel they are brushing frequently are often missing areas of the tooth, or are using too hard of a brush," Dr. Haywood says. He recommends using a staining material (available at most drug stores) and then 'brushing the red out' can help you make sure you are thoroughly brushing all areas of your teeth.

"However, over-aggressive brushing can be counter-productive, as it may remove enamel and make the tooth look darker. It also may cause the gums to recede," Dr. Haywood notes.

He also advises waiting 30 minutes after eating to brush. That allows saliva to remineralize tooth enamel that may be weakened from acidic foods.

How to whiten

There are many over-the-counter (OTC) products as well as in-office bleaching that will brighten your smile. How do you choose? The best first step, according to the American Dental Association (ADA), is to talk to your dentist for a recommendation before undergoing any whitening method.

Dr. Haywood explains it's especially important to have a dentist determine the cause of darkening of your teeth prior to bleaching, especially if you have a single dark tooth or teeth. The dentist will perform a complete exam including x-rays to look for potentially serious causes of discoloration that can include abscessed teeth, internal resorption (dissolving away of the inside of the tooth from previous trauma), external resorption, cavities (tooth decay), discolored restorations (fillings), or even, rarely, tumors.

If your dental health is good and you are ready for a brighter smile, how well do whitening toothpastes work? "They can maintain a whiter tooth. But they don't change the inherent color of the tooth," Dr. Haywood says. "So they would be the best option for maintenance. To be effective in actually lightening teeth, you need either a hydrogen peroxide (HP) or carbamide peroxide (CP) product, and it needs to stay on the tooth with some barrier protection (a tray or strip), for 30 to 60 minutes minimally."

Carbamide peroxide works best when used for hours, especially overnight. However, you'll need a dentist to fabricate a dental tray for you if you use CP overnight. Otherwise, you can use an OTC tray for several hours during the day. You can achieve the same whitening with HP as with CP, Dr. Haywood explains. But it will take many more days or weeks for hydrogen peroxide.

"Whatever you purchase OTC, you must limit your application to the manufacturer's instructions, since some of the hydrogen peroxide products are very acidic (the most popular OTC product has a pH of 5, and enamel dissolves below pH 5.8)," he cautions.

Professional teeth whitening by your dentist

Opting for do-it-yourself lightening may work fine for you. However, in-office bleaching uses higher concentrations of bleaching product (and, sometimes, a special light that speeds whitening) and can zap your teeth to a lighter color in an average of only three visits.

Your dentist can also help sooth any sensitivity issues that can impact how well you tolerate bleaching. "Sensitivity is always an issue for some people. So a history of sensitive teeth means you need to use a lower concentration of the bleaching product and take preventive steps," Dr. Haywood says. "Sensitivity is best treated with potassium nitrate-containing materials for brushing, or in a tray and may need to be started two weeks prior to bleaching to minimize sensitivity."

Does bleaching have any effect on existing dental work, such as fillings, veneers, or crowns? "Tooth-colored composite (plastic resins) or ceramic (porcelain) tooth restorations can't be lightened with bleach, so they remain the same color. Therefore, you will have to consider what your smile will look like if your natural teeth get lighter but your restorations do not," Dr. Haywood answers. "This is a good topic to discuss with your dentist, who can run through the options in your particular case."

Once your teeth are as white as you want, how long will your bright smile last? While no bleaching method whitens teeth permanently, usually the results last from six months to two years. However, some lucky people's teeth remain white after bleaching for over 10 years with no touch-up treatment, according to Dr. Haywood. To keep your newly whitened teeth as stain-free as possible, he recommends keeping up with your regular oral hygiene routine at home and your professional cleanings at your dentist's office. "Also consider a bleaching touch-up once or twice a year at home or at the dentist's office," Dr. Haywood adds.