Cavities: How they develop

Please provide me with some information about the bacteria that causes cavities and tell me how cavities develop?


There are three essential factors that determine how cavities develop: 1) natural tooth structure exposed to the oral cavity; 2) dental plaque; and 3) substrate or food. There are other modifying factors which affect the location of cavities and their progression, but the factor you are most interested in is plaque.

Plaque is composed of bacteria and their by-products. Dental plaque is actually quite complex. The accumulation of plaque on teeth is quite organized and takes place in a certain sequence. First, the bacteria must adhere to tooth structure. Primarily, certain species of Streptococci are able to create a sticky matrix which allows them to adhere to clean tooth structure. Once they adhere, they multiply to form a matlike covering so other organisms can come along and adhere to the mat. The formation of plaque undergoes many changes and each change is dependent upon the previous step.

Due to the complex nature of plaque, it has been difficult to determine the exact causative agents of dental caries. Streptococcus mutans has been the most widely accepted causative agent of caries in the enamel of teeth (the outer layer of teeth). Later in the 19th century, W.D. Miller started the search for a single causative agent. From about the 1920s to 1950s, Lactobacillus acidophilus appeared to be the main factor. Large numbers of this species were found in the mouths of patients who had many cavities. It seemed these bacteria could be found with regularity prior to formation of any decay. In addition, they have the ability to survive and to produce acid in a low pH environment. It is acid production by bacteria which ultimately leads to carious lesions (cavities.)

As time has passed, however, large amounts of Lactobacillus acidophilus were also discovered in the mouths of patients who had no cavities; therefore, there are arguments that cavities are not caused by this single agent. In fact, the Lactobacillus species do not have the ability to adhere to tooth surface, so it is unlikely to be the initiator of dental decay, but it does bear some responsibility for the spread of decay in dentin (the layer of tooth beneath enamel.)

The three most implicated bacteria in causing dental decay are Streptococcus mutans, Lactobacillus species, and Actinomyces species. There are some cause and effect relationships which are recently being questioned. Other factors, such as diet and oral hygiene may play a larger role in the formation of cavities than the actual bacteria, since many of these bacteria are normally present in the oral cavity. Other factors, such as systemic diseases, genetics, saliva composition, the biochemical composition of the teeth, and the presence of fluoride, continue to be studied for their roles in the formation of cavities. Thanks for the good question.

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