Tooth decay begins when bacteria, particularly Streptococcus mutans, accumulate on the teeth in the absence of adequate oral hygiene, forming plaque. Bacteria metabolize fermentable carbohydrates, leading to acid formation and a decrease in plaque pH. Frequent or sustained drops in pH can result in progressive demineralization of the enamel, ultimately leading to caries. The etiology of caries is a combination of elements: susceptible teeth, dental plaque, food and the length of time food remains in contact with the teeth.
Prevention of dental caries, therefore, requires several measures. It is well known that fluoride is a primary factor in the control of dental caries and can significantly reduce caries. Other intervention methods include control of fermentable carbohydrate intake, proper oral hygiene, and the application of plastic sealants. There may even be a hereditary disposition to caries resistance.
While sugars have been implicated in the development of dental caries, it has long been known that any food containing fermentable carbohydrates - including cooked starches such as bread, cereal, crackers, etc. - can promote caries formation. The cariogenicity of food is related to the amount of total fermentable carbohydrates. It is often assumed that starchy foods such as potato chips and bread are not a factor in caries development because oral bacteria cannot break down starches into acids. However, most starchy foods are retained in the mouth long enough to mix with saliva, which contains the enzyme "amylase" that converts starches into sugars, which the oral bacteria then can metabolize to acids. In fact, sugars such as sucrose and fructose tend to be less cariogenic than starch because they dissolve in water and saliva, and are removed from the mouth more rapidly. Processed high-starch snacks, whether gelatanized, baked or fried, produce as much acid in plaque as sucrose alone, but at a much slower rate. Thus, the cariogenicity of food is not necessarily related to its sugar content. Foods that are 50 percent sugar do not necessarily cause more tooth decay than foods that are 10 percent sugar.
It is difficult to categorize foods by degree of cariogenicity. Certain non-carbohydrate characteristics of a food (e.g., fat, protein, minerals, buffering capacity, water content, texture) can modify cariogenicity, as can the sequence of food consumption. The frequency of exposure to carbohydrate-containing foods plays an important role. Eating more than five-to-six times per day and continuous nibbling or sipping of foods and beverages promotes tooth decay.
The retention time of food on the teeth also impacts cariogenicity. Recommendations to avoid sticky foods may be misleading. A food such as a caramel or jelly bean is initially sticky, but then quickly clears the mouth. In a study of the perceived stickiness verses actual retention of 21 commercially available foods, Kashket et al. found that cookies, crackers and potato chips were more retentive than chocolate bars, caramels, jelly beans and raisins.
Cocoa is not intrinsically cariogenic because it does not contain significant fermentable carbohydrate. For that reason, unsweetened chocolate is not considered a contributing factor in the development of caries in animals or humans, or in measures of plaque formation, acidity, or enamel demineralization. Chocolate's lack of cariogenicity may hold true even when chocolate is sweetened. Researchers for the classic 1950s Vipeholm study in Sweden reported no statistically significant difference in the incidence of dental caries among a control group that consumed no sweets and another group that consumed chocolate.
The results of several studies counter the common misconception that sweetened chocolate is highly cariogenic. Morrissey et al. tested the cariogenicity of several common snack foods on rats, and found solid milk chocolate among the lowest in cariogenicity of all the foods evaluated. A study that specifically examined food retention found that chocolate bars cleared the mouth rapidly because they contain fat, despite the fact that subjects rated chocolate bars as fairly sticky.
Moreover, certain naturally occurring substances such as tannins in cocoa may play a role in the inhibition of dental plaque formation. Yankell et al. found that mixtures of sucrose and chocolate, cocoa, or confectionery coating at ratios commonly used in candy were less cariogenic in human subjects than a 10 percent sucrose solution, as measured by plaque pH and plaque ionized calcium. This may be due to the tannins or other undefined components in chocolate.
* Bibliography of scientific journals referenced here available upon request.