Bacteria Causing Dental Caries

Dental caries is a microbial disease that results in the destruction of the mineralized tissue of the teeth. It is believed that it is initiated by lactic, butyric and other organic acids such as acetic acid, propionic acid, glutamic, and aspartic acid which are production is a result of bacterial fermentation of carbohydrates on the tooth surface. Bacteria thought to be responsible for dental caries include Actinomyces odontolyticus, Lactobacillus species, and Streptococcus mutans. The acids produced by these bacteria reduce the pH of the mouth to less than 5.0 at which decalcification occurs and dental decay begins.¹ The rise in the pH is slower and it depends upon the ability of saliva to neutralize acids. The pH 5.5 is called critical because below this pH demineralization of tooth surface begins.²

Because Lactobacillus species are poor colonizers of smooth surfaces, they probably do not initiate caries at these sites. Most likely Lactobacilli are secondary colonizers of established caries lesions where their acid-producing ability allows them to outcompete other organisms. Acid production will then exacerbate the lesion and facilitate extension into the dentin. If Lactobacilli become trapped into pits and fissures they may ba able to initiate caries in these sites.³

Recent molecular biology approaches have demonstrated the diversity and complexity of the microbial community associated with caries and is believed to be far greated than anticipated. Other bacteria species such as Bifidobacterium and Atopobium have been suggested to participate in the development of caries.⁴ As the caries lesions advance deep into dentin, the microbial predominance shifts to Lactobacilli and proteolytic bacteria; species occurring in abundance in these deep lesions include Selenomonas, Dialister, Fusobacterium, Eubacterium, Olsenella, Bifidobacterium, members of the Lachnospiraceae, and Pseudoramibacter alactolyticus. Most of these bacteria have also been detected in infected root canals.⁴

Excess Carbohydrate Consumption Linked To Dental Plaque

The resident bacteria in the mouth ferment carbohydrates to yield acidic end-products (mainly lactic acid, but also some formic, acetic, and propionic acids), which results in a drop in a dental plaque pH. When the pH falls below 5.5, the dental enamel dissolves in the plaque fluid. Repeated exposure to periods of very low pH can lead to dental cavities (caries). Agents capable of causing caries are called cariogenic.

Not all carbohydrates are equally capable of causing caries. The sugars found commonly in human foods, for example sucrose, fructose, glucose, and maltose are all readily fermented by bacteria in the mouth. Lactose, galactose, and starches are less cariogenic, while sugar alcohols such as xylitol (used as a sweetener in some confectionery and chewing gums) are noncariogenic. Eating sugar with meals reduces the risk of caries, as does the consumption of cheese, which provides phosphates to prevent demineralization of the enamel.⁵