Fluoridation and such innovative techniques as sealants have dramatically reduced the problem of tooth decay. Yet it has hardly become a medical curiosity. Many people have not been exposed to fluoride, and still more have not experienced the benefits of sealants. Even many who have had both are acquainted with the dentist's drill. So, despite all the progress, diet continues to play an important role in preventing tooth decay.

Our mouths normally harbor a vast population of bacteria. These microscopic organisms feed on carbohydrates in food left in the mouth, making acid byproducts that can erode the enamel surfaces of teeth. Over time, this process can demineralize a tooth and bring on decay.

Sugar is a major culprit in the formation of dental caries, or cavities. The more often we eat sugary foods, the more likely we are to do damage. Foods loaded with table sugar, or sucrose (cakes, cookies and candy), are the natural enemies of tooth enamel. So are other simple carbohydrates, such as honey and corn sweeteners added to processed foods. The high sugar content and stickiness of certain fruits, especially when dried, increase the decay-causing potential of these foods as well.

Food texture also is important. Fibrous foods such as fruits and vegetables may help to protect against caries because the increased chewing and salivation associated with fiber may promote a cleansing action. Sticky foods, on the other hand, may be particularly rich in sugar and also adhere to tooth surfaces. Raisins, dates and caramels linger in the mouth and give bacteria a longer time to work. Some 2,400 years ago, Aristotle observed that the habitual consumption of raisins and figs caused dental decay. According to a study reported in the Journal of the American Dental Association (JADA), raisins caused more damage in laboratory animals than 10 other snack foods, including granola bars, chocolate-covered cookies with caramel, and fudge bars. This does not mean these foods are nutritionally superior or a better snack choice than raisins, but only that eating dried fruit calls for thorough oral hygiene afterwards.

Since sticky foods can make acid as long as they remain on or between the teeth, it makes sense to consume them as part of a meal, rather than as snacks. Other foods eaten at the same time, along with the saliva produced during the chewing process, can then help wash these carbohydrates out of the mouth. But the traditional policy remains best: brush or floss after eating.

Besides carbohydrate content and stickiness, a third important factor in the development of caries is the length of time spent consuming a particular food. Within 20 minutes after eating, bacteria in the mouth reach their peak acid-forming activity. A candy bar eaten all at once and then rinsed out by water or brushing might expose the teeth to acid for less than 20 minutes. Sucking a lollipop could mean exposure at least twice as long.

The national passion for sweetened beverages, particularly soft drinks, is another concern. Since they are liquid and easily rinsed, you might think such drinks would be less harmful than other snacks. But they are often consumed between meals, or sipped over a long period of time. This can lead to prolonged acid exposure.

Studies demonstrate that soft-drink consumption at and between meals could be used to predict high DMFT (decayed, missing or filled teeth) scores. The average American consumes the equivalent of 420 12-ounce cans of soft drinks a year. That figure is still on the rise, even among toddlers and young children.

Many foods can cause tooth decay, but are there any that can help prevent it? Research indicates "yes, with qualifications." In the JADA study, the snack food with the lowest potential for causing cavities was aged cheddar cheese, which has little fermentable carbohydrate. The milk proteins in the cheese, especially casein, seem to help tooth enamel resist the demineralization caused by acids. The fat in the cheese may offer additional protection.

Sugar substitutes seem relatively easy on teeth, too. The sugar alcohols -- sorbitol, mannitol and xylitol -- do provide calories, but resist fermentation by most bacteria in the mouth, or are fermented very slowly. And there is no reason to think saccharin or aspartame will cause caries.

Finally, chocolate lovers may be giving their teeth some advantage by choosing chocolate over caramels. Laboratory studies have shown that a substance in cocoa butter appears to prevent cavities. But chocolate candies and cocoa are sweetened with sugar, and any protective factor does not offset the sugar's attack on tooth enamel.

Restricting sweets to meal times, limiting cavity-producing snacks and following the rules of good oral hygiene are no less important today than in the era before fluoridation and dental sealants.