What Causes the Appearance of Dental Caries?

Tooth decay, which leads to the progressive destruction of the tooth, is an infectious disease that always develops from the outside to the inside. If left untreated, it can reach dentin, the layer beneath the enamel. At this stage, the tooth becomes painful to certain stimulations such as chewing. The decay is then active and can then affect the pulp, the innermost layer of the tooth. This is why you should not wait to see your dentist. Children, especially young ones, are most affected. We are talking about early childhood caries, occurring before the age of six on milk teeth, with enamel thinner than that of permanent teeth. Early childhood caries, in addition to adult caries, represent a public health problem in France.

[Article issu de The Conversation, écrit par Valérie Lannoy, Post-doctorante en microbiologie, Sorbonne Université]

Acidity demineralizes the tooth

Enamel, the outermost layer of the tooth, is also the hardest in our body. It is made of the same mineral found in bones, hydroxyapatite. Although mineral, enamel is in fact a dynamic structure, which follows regular cycles of demineralization and remineralization. In the event of disruption, the cycle becomes unbalanced in favor of demineralization.

Hydroxyapatite is a calcium phosphate, whose phosphate group is particularly sensitive to acids. An environment rich in acid leads to demineralization, since the phosphate separates from the calcium, and this is the birth of cavities! Enamel is in direct contact with dental plaque, a natural biofilm composed of our oral microflora, the bacteria we normally harbor in our mouth.

Enamel is therefore weakened when an event acidifies dental plaque. For example, the consumption of alcohol and tobacco promotes the appearance of cavities because they affect the salivary glands, which reduces saliva secretion. However, saliva reduces the acidity of the oral cavity. Another factor that can acidify our dental plaque is simply its composition: oral bacteria. These are commensal bacteria whose role is to predigest part of our food, and some of which are “acid” bacteria. These bacteria, Streptococcus mutans And Lactobacillus acidophilusferment sugar into lactic acid. What causes cavities is indeed an imbalance, i.e. the abnormal proliferation of bacteria, and not their presence itself.

An excess of sugar in the diet allows these bacteria to grow faster, and a vicious circle sets in as they ferment this same sugar into lactic acid.

The leading role of sugar

In 2021, it was discovered that the oldest evidence of tooth decay dates back 54 million years. It was found on fossilized teeth of Latid microsyopsa small primate which lived when the first fruit trees appeared, and whose diet was therefore enriched with sugar. No trace of dental caries has also been found on any animal other than a mammal, the class of vertebrates of which certain species are frugivorous, herbivorous or omnivorous. Also in 2021, an international collaboration demonstrated that, contrary to popular belief, wild primates suffer from cavities, particularly small fruit-eating monkeys. Their diet is a source of fermentable sugars in the mouth. 30,000 years ago, Neanderthals were fond of dates, a fruit considered to promote decay. However, its rate of cavities is low, probably due to its diet, which is nevertheless low in fruit and rich in meat.

In the human species, the first cavities appeared 11,000 years ago, during the Neolithic revolution. Sedentary lifestyle has allowed the emergence of cavities, particularly with the consumption of flour. One of the professions most affected by cavities is the baker, due to his professional atmosphere filled with suspended flour! Flour is made up of 70% slow sugars, which saliva digests into fast sugars, themselves fermented by acidic bacteria.

How to protect yourself from cavities?

Caries is the most common oral disease in the world, but also the most preventable. You can allow yourself sweet pleasures, as long as you brush your teeth! The most famous active element in toothpastes is fluoride, because it remineralizes enamel into a less soluble form than hydroxyapatite, i.e. fluorapatite. But whatever the composition, the most important thing is to respect hygiene, which will prevent the thickening of dental plaque!