Acid Production

When food or drink containing fermentable carbohydrate is consumed, the pH of plaque begins to drop. Fermentable carbohydrates include both sugars and starches. Sugars may be sucrose, fructose, lactose, maltose, and glucose. Of these, lactose is the least cariogenic. Acids are produced when plaque bacteria metabolize carbohydrate. At a pH below 5.5 (the critical pH), the acids can begin to demineralize enamel and dissolve tooth structure.5 This may last for 20 to 30 minutes until the buffering action of saliva neutralizes the acidity of plaque. In areas between teeth or in fissures on occlusal surfaces of teeth, the pH may drop to as low as 4.0 and may persist for one or more hours.

Starches found in breads, cereals, pastas, rice, and some vegetables are also fermentable. However, the effect of starch-containing foods on teeth depends on whether the starch is raw, cooked, or refined and whether sucrose is present. Compared to sugars, the time required to initiate the caries process is somewhat longer for starches as salivary amylase, an enzyme, must first hydrolyze large starch molecules into maltose. Fermentation of maltose yields acids that demineralize enamel rapidly. Cereal grains, which are refined and cooked in the production of breads or crackers, are more easily hydrolyzed by salivary amylase. Starch and sugar mixtures, as found in ready-to-eat breakfast cereals, some breads, pastries, and many convenience foods, are retained in the plaque that lodges between teeth, making these foods even more cariogenic than sugars alone.11,12 In fact, foods with a higher content of sugar are removed more rapidly and depress the pH of plaque for a shorter time than starchy foods.13

Raw starches found in vegetables have low cariogenicity. Fruits on the other hand contain both raw starches and sugars. Despite the sugar content, fresh fruits also have a low cariogenic potential, especially when eaten with meals. This is attributed to the high water content of fruits and the presence of citric acid, which stimulates saliva secretion. Sugars in soft drinks, fruit drinks, fruit juices, and sports drinks are less cariogenic to teeth than solid sweets because beverages clear the mouth more quickly. However, frequent between-meal intake of sweetened beverages or slowly sipping sugar-sweetened drinks, such as soda, coffee, or tea, bathes the teeth with sugars that are easily fermentable and increases caries risk.14
(Early child-hood caries caused by inappropriate feeding practices is discussed in more detail in the sidebar, Baby Bottle Tooth Decay.)