It has been discovered that the primary species of bacteria involved in initiating approximately 95% of all dental caries lesions is Mutans streptococcus. These oral bacteria contain an enzyme called glucosyltransferase on the exterior of their cell membranes. This enzyme only uses sucrose, or table sugar, as its substrate. Sucrose stimulates the production of more glucosyltransferase units on the surface of Mutans streptococci bacteria. Therefore, if sucrose levels rise in the oral cavity, glucosyltransferase levels on Mutans streptococci are subsequently elevated. .
Glucosyltransferase enzyme is located on the exterior surface of the cell membrane of Mutans streptococci, leaving the enzyme capable of interacting with the external environment. In the oral cavity, whenever sucrose is available, the GTF enzymes on Mutans streptococci convert sucrose into glucose and fructose, yielding energy. The glucose monomers are linked via alpha 1,3 linkages into a glucan, a polysaccharide of only glucose molecules. The glucan molecules form an insoluble coat around the Mutans streptococci that seal the lactic acid produced by the bacteria against the surface of the tooth. With this polysaccharide glucan barrier formed, the buffering capacity of the saliva is unable to reach the lactic acid, the most acidic acid a bacterium can produce. Lactic acid production can be dangerous in increased concentrations that cause a drop in pH. A pH of 5.5 or lower facilitates the dissolution of hydroxyapatite crystals formed in the teeth, which results in the formation of dental caries. .
Saliva has a dual functionality in that it coats the teeth and the bacteria present in the mouth. With both of these coats intact, bacteria are unable to bind to the teeth, thus preventing the formation of dental plaque. In order for a bacterium to bind, it must first produce some special proteases to digest the salivary coating on its cell membrane.
