tooth health

What bacteria cause tooth decay?

Caries is caused by some bacteria present in the oral cavity, which feed on the sugars introduced with the diet, producing acid metabolites with a corrosive action on the hard tissues of the tooth.

The human oral cavity hosts several hundred microbial species, but only some of these are implicated in the etiopathogenesis of caries. The most important and known cariogenic species is Streptococcus mutans ; however, in carious lesions other cariogenic germs can be found, including streptococci ( S. oralis , S. sanguis , S.mitis ), lactobacilli and actinomycetes.

In addition to fermenting some carbohydrates taken with the diet (especially saccharose, glucose, fructose and lactose), these microorganisms show important adhesive abilities on the tooth surface, to which they anchor, giving rise to plaque.

The acids produced by the bacteria demineralize the inorganic component of the enamel and dentin, while proteolytic enzymes of bacterial origin also attack the organic component of these tissues.

Acidogenic bacteria also have the ability to tolerate low pH levels, which combine to select them at the expense of other commensal species, thus establishing a vicious circle that feeds the progression of caries.

The modern theory on the etiopathogenesis of caries was developed at the beginning of the last century. In 1915 Klinger demonstrated the presence of Lactobacilli in carious lesions, and at least until the 1960s these bacteria were considered - wrongly - the main microorganisms responsible for caries. It was not until the 1960s that Streptococcus mutans - for the first time isolated from Clarke in human carious lesions in 1924 - was re-proposed as the main responsible for caries by various groups of researchers.

The action of cariogenic bacteria is counterbalanced by saliva, thanks to its content of molecules such as:

  • bicarbonate, able to buffer the acid pH;
  • calcium, phosphate and fluorine ions that replace the crystalline structure of the enamel altered by acids;
  • lysozyme and lactoferrin (enzymes with antibacterial properties) and immunoglobulins (antibodies);
  • water, whose washing action reduces both the bacterial density and the food residues, removing the nourishment from the bacteria responsible for caries