Bacterial Causes of the Variation in Caries Susceptibility

The microbiota of the oral cavity forms within a few months of birth and is stable thereafter. The types of bacteria present in the biofilm adhering to teeth, and therefore the extent of caries development depends at least in part on that microbiota. Individual differences in microbial composition cause individual variation in caries development. 

In addition to variations in a biofilm s polymer content related to sucrose consumption, bacteria that metabolize salivary urea or dietary arginine also affect biofilm pH. The enzyme urease converts salivary urea to ammonia and carbon dioxide (Sect. 12.1.2), 

Counts of the number of S. mutans or L. casei are a poor measure of caries susceptibility because as noted above, they cannot account for ammonia production or differences in glycan production by other bacteria in the biofilms. Acid production after a 10% sucrose or glucose rinse after a 6 h or longer fast is a better measure of caries susceptibility, because it represents the balanced outcome of the factors that promote or prevent caries. Because this method requires time and skill, it is difficult to apply to many subjects. A simpler method of measuring caries susceptibility is past caries experience and age. The more teeth affected by caries in a child or adolescent, the greater is the likelihood that a new cavity will develop and, therefore, the greater is the need for preventive measures. Unfortunately, this measure is completely uninformative about what factors are present to promote or prevent caries. 

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