The right kind of chewing gum lowers the risk of tooth decay

Q: Why do dentists recommend chewing gum? Doesn't gum cause cavities?

A: Dentists don't recommend just any chewing gum. They recommend sugar-free gum, specifically gum that contains xylitol, a sugar-free, no-calorie sweetener made from the bark of birch trees. It may actually lower your risk of tooth decay and cavities by interfering with the growth of harmful mouth bacteria.

Bacteria in your mouth eat sugar or starch that is found in the foods and beverages you consume. Fueled by this energy, they grow, multiply and form plaque. That's the bacteria-laden film that covers your teeth between brushings.

Bacteria eating sugar and starch give off acidic waste that attacks tooth enamel. This acid in the plaque sets the stage for tooth decay, cavities and gum disease.

But bacteria in the mouth can't digest xylitol. That's why this sweetener inhibits the growth of mouth bacteria and reduces the production of plaque and destructive acids.

Xylitol may also prevent the production of a substance that helps plaque bacteria stick to teeth.

University of Minnesota researchers studied the effects of chewing gum on mouth bacteria. They asked one group of volunteers to chew gum sweetened with xylitol for five minutes after each meal.

Another group chewed a gum with sorbitol, another sugar-free sweetener. A third group didn't chew gum at all. After three months, the number of bacteria in the saliva of xylitol-gum chewers was lower than in the other two groups.

To reap these benefits, chew a piece of xylitol gum three or four times a day for at least five minutes. Sugarless gum without xylitol doesn't seem to cut down on bacteria, but it can help increase the flow of saliva, which protects teeth.

Carbohydrate-containing foods, including bread, cereal, rice, other grains, beans, fruits and vegetables, contain sugars and starches that feed the bacteria that live in your mouth. However, these foods are part of a healthy, balanced diet.

But there are other types of starches and sugars that promote cavities and are not part of a healthy diet. For many reasons, not just preventing dental problems, it's best to minimize them in your diet:

• Sticky sweets such as honey, molasses, chewy candy or raisins.

• Slowly dissolving sugars, such as those from slow-melting hard candies.

• Starch and sugar combinations, such as those found in cookies, cakes and other sweet baked goods.

Finally, if you eat sweets before bedtime, be sure to brush before heading to bed. Otherwise, the sugar will stay in your mouth and on your teeth overnight.

If you have had many cavities, or gum disease, you might talk to your dentist about using sugar-free gum with xylitol after every meal. Also ask your dentist about the value of these practices:

• Brushing your teeth after every meal;

• The best toothpaste for you;

• Whether the tap water in your community is fluoridated.

• Dr. Anthony Komaroff is a physician and professor at Harvard Medical School. To send questions, go to AskDoctorK.com, or write: Ask Doctor K, 10 Shattuck St., Second Floor, Boston, MA 02115.