How does saliva protect us from disease?

Bacteria in the mouth (oral flora)

The number of bacteria in the mouth is huge! Researchers estimate that billions of bacteria and around 500 different species can be found in the oral cavity. Even today, researchers are still discovering previously unknown subtypes of bacteria. These microorganisms can be divided into “good” and “bad”, that is, disease-causing.

Some bacteria need oxygen for their metabolic processes (aerobic), while others can do without the gas from the air (anaerobic). Their “food” is, for example, protein and sugar from leftovers. Some microbes are permanent guests (resident), others only romp around temporarily in the oral cavity (transient).

There is usually an elaborate balance between the microorganisms in the oral flora because they keep each other in check. However, if the oral flora is “damaged”, dangerous pathogens multiply, get out of hand and cause problems in the mouth, gums and teeth.

The oral flora must develop over time. A fetus in the womb does not yet harbor bacteria in its mouth. But microorganisms begin to colonize the oral cavity immediately after birth. Usually the first bacteria in the mouth are streptococci. Various other types of bacteria later appear as part of the oral flora, such as staphylococci or pneumococci.

After all, the composition of the oral flora becomes more and more complex - especially when the first teeth erupt. During puberty, the oral flora changes again significantly due to the hormonal change (similar to that during pregnancy). The gums are supplied with more blood and are softer. Under these conditions, it is easier for bacteria to settle in the gums and, for example, to cause inflammation of the gums.

Good bacteria in the mouth

Most bacteria in the mouth are considered harmless and do not cause any damage to teeth or gums. Some "good" bacteria in the mouth also have a protective function. They act as a “protective force” and even promote oral and dental health.

This is an example useful bacterium Streptococcus salivarius, which has anti-inflammatory properties and displaces germs. The bacterium is one of the first to settle in the oral cavity. The bacterium too Streptococcus sanguinis fights pathogenic germs and prevents tooth decay. It colonizes the oral cavity when teeth begin to grow.

Dangerous bacteria in the mouth

In addition to the "good" microbes, there are also dangerous bacteria in the mouth that promote tooth decay (cariogenic microorganisms) or gum disease:

  • Streptococcus mutans: This bacterium is the main actor in the development of tooth decay. Parents transmit these bacteria to their children when they kiss or when they lick the pacifier and then stick it in the child's mouth. Caries bacteria metabolize the sugar from food and produce acids, especially lactic acid. This attacks the tooth enamel and creates holes in the teeth. Streptococcus mutans feels most comfortable in the plaque.
  • Streptococcus mitis is part of the normal oral flora, but under certain conditions (e.g. increased sugar consumption) it is associated with the development of tooth decay.
  • Lactic acid bacteria (Lactobacilli) and Pus bacilli (Fusobacteria) promote tooth decay.
  • Actinomycetes cause infections of the oral cavity.
  • Veillonella parvula causes tooth decay under certain circumstances, such as a weakened immune system.
  • Putrefactive bacteria often settle on the tongue and cause bad breath.
  • The Actinobacillus actinomycetemcomitans bacterium is particularly dangerous and responsible for diseases of the tooth supporting system (periodontitis). The germs Porphyromonas gingivalis, Prevotella intermedia, Tannerella forsythia and Treponema denticola also play an important role in periodontitis. In the course of periodontitis, the composition of the community of microorganisms changes: atypical representatives can appear, for example Escherichia coli bacteria in the mouth, which further aggravate periodontitis. Usually, however, they prefer to live in the intestines.