Dental Caries: Role of Carbohydrates in Caries Development
Dental caries (cavities) is a common plaque-dependent bacterial infection that is strongly affected by diet. Development of a cavity is contingent upon the interaction of three factors in the mouth: a susceptible tooth, cariogenic (cavity causing) bacteria, and fermentable carbohydrate (sugar). Absence of one of these factors dramatically reduces caries risk. Mutans streptococci are the predominant oral bacteria that initiate the caries process. Plaque bacteria ferment starches and sugars, producing acids. These acids demineralize dental enamel which weakens and chips away, resulting in a “cavity.”
Other dietary factors counteract the damaging effects of carbohydrates. The presence of protective minerals and ions such as fluoride, calcium, and phosphorus in plaque and saliva, promote remineralization of incipient lesions (cavities limited to the enamel). In addition to transporting minerals, saliva contains buffering agents, bicarbonate and phosphates, that neutralize acids. Thus, the amount and composition of saliva affect the caries process. Other host factors that influence caries risk include: genetic predisposition, immune status, malnutrition during tooth formation, education level, and income status.
The amount of sugar consumed is not the sole dietary variable associated with caries development. Sucrose plays a more dominant role than other sugars in the development of smooth surface caries. One of sucrose’s metabolic by-products, an extracellular polysaccharide called glucan, enables the bacteria (mutans streptococci) to adhere to the smooth enamel surfaces, thus enabling the bacteria to stick to the teeth.
The use of sugar alcohols and alternative sweeteners in foods also has had a role in reducing caries. Perhaps one of the most promising sugar substitutes to be studied is xylitol, a sugar alcohol that has been demonstrated to be non-cariogenic as well as promoting remineralization. Xylitol’s ability to inhibit metabolic acid production by mutans streptococci results in minimal depression of plaque pH. Maintenance of the plaque pH close to the saliva pH also fosters remineralization of teeth. In addition, the substitution of xylitol for fermentable sugars in the diet results in a less cariogenic bacterial flora.
Simple sugars are not the only carbohydrate that influences the development of a carious lesion. Highly refined cooked starch-sugar combinations such as doughnuts, cookies, potato chips, and some ready-to-eat breakfast cereals produce a prolonged acidogenic response when retained in interproximal spaces. When starches are cooked, they are partially degraded. This allows the salivary alpha-amylase to convert starch particles retained on the tongue, oral mucosa, and teeth to maltose. Making maltose available to plaque bacteria extends the length of time the plaque pH will remain low and permit enamel demineralization to occur. Thus, retentive high starch foods may be more acidogenic than high-sugar-low-starch foods that are rapidly eliminated from the mouth.
Effects of Eating Patterns and Physical Form of Foods
Other dietary factors that may hinder or enhance caries development include: the frequency of eating, the physical form of the carbohydrate (liquid vs. solid), retentiveness of a food on the tooth surface, the sequence in which foods are consumed (e.g., cheese eaten before a sweet food limits the pH drop), and the presence of minerals in a food.
Frequent between-meal snacking on sugar or processed starch-containing foods increases plaque formation and extends the length of time that bacterial acid production can occur. Frequent snacking between meals keeps the plaque pH low and extends the time for enamel and dentin demineralization to occur.
Bacterial fermentation can continue as long as carbohydrate adheres to the enamel and exposed dentinal tooth surfaces. Even though starchy foods vary in their cariogenic potential, the highly refined starchy foods, such as soft bread and potato chips, that are retained on tooth surfaces for prolonged periods of time, result in a lowered pH which may last up to 60 minutes. High-sucrose confectionery foods deliver high levels of sugar to the oral bacteria immediately after the foods are consumed, whereas high-starch foods deliver progressively increasing concentrations of sugars over a considerably longer period of time.
The sequence in which foods are eaten affects how much the plaque pH falls. Sugared coffee consumed at the endof a meal will cause the plaque pH to remain low for a longer time than when an unsweetened food is eaten following intake of sugared coffee. If peanuts are eaten before or after sugar-containing foods, the plaque pH is less depressed.
Some components of foods are protective against dental caries. Protein, fat, phosphorus, and calcium inhibit caries. Aged natural cheeses have been shown to be cariostatic. When cheese is eaten following a sucrose rinse, the plaque pH remains higher than when no cheese follows a sucrose rinse. In addition, enamel demineralization, measured using the intraoral cariogenicity test, is reduced. The protective effect of cheeses is attributed to their texture that stimulates salivary flow, and their protein, calcium, and phosphate content that neutralizes plaque acids. Fluoride found in drinking water, foods, and dentifrices increases a tooth’s resistance to decay and enhances remineralization of carious lesions.
Lipids seem to accelerate oral clearance of food particles. Some fatty acids, linoleic and oleic, in low concentration, inhibit growth of mutans streptococcus. Lectins, proteins found in plants, appear to interfere with microbial colonization and may affect salivary function.
Early Childhood Caries (baby bottle tooth decay or nursing caries)
One of the most severe forms of caries occurs in infants (also called baby bottle tooth decay or nursing caries). Inappropriate feeding practices result in progressive dental caries on the buccal and lingual surfaces of newly erupted teeth of infants and toddlers.
Primary risk factors for early childhood caries include putting a child to sleep at naptime or bedtime with a bottle containing a liquid other than plain water, allowing an infant to breast-feed at will during the night, and extended use of the nursing bottle or sippy cup beyond 1 year of age. Inappropriate feeding practices were reported more often by parents with less than a high school education, low incomes, Hispanic backgrounds, and those parents whose children had not been to a dentist in the past year. Children who develop maxillary anterior caries are at increased risk of developing posterior caries in the future.
- Eat a nutritionally adequate diet following the food pyramid guidelines.
- Increase the use of saliva-stimulating fibrous foods.
- Multivitamin/mineral supplements should be in doses no higher than one to two times Recommended Dietary Allowance levels.
- Avoid fad diets which could be deficient in nutrients.
- Avoid single vitamin supplements.
- Avoid potentially detrimental megadoses of vitamins and minerals (10× RDA or higher).
Eating disorders, especially bulimia, are often first diagnosed in the dental office. Patients, usually young females, present with severe erosion of the lingual tooth surfaces. The oral tissues are often red, sore, and painful. The esophagus may be inflamed, and parotid salivary glands are often swollen. Bulimia is characterized by recurrent episodes of binge eating (consumption of large amounts of foods at a time) followed by self-induced regurgitation (purging). Patients may also use laxatives and/or diuretics to induce malabsorption and fluid loss. The acid from stomach regurgitation irritates the esophagus and the oropharyngeal soft tissues. The regurgitated acid in combination with xerostomia, results in rapid and extensive destruction of tooth enamel.