What is tooth decay and how does it develop?

Tooth decay is the most widespread non-communicable disease in the world. In Germany, too, every adult is affected by caries on average several times during his or her life.

In order to understand exactly how caries develops, let's take a closer look at the structure of the tooth: The tooth consists roughly of two parts - the tooth root and the tooth crown. The root of the tooth is in the jawbone.

The crown of the tooth, on the other hand, protrudes “unprotected” into the oral cavity. This tooth crown gets the caries. Plaque builds up on their surface every day just from the flow of saliva and food intake. Malignant bacteria settle within this plaque, which in turn causes tooth decay. This happens as follows: The outer, visible part of the tooth crown is made of tooth enamel. This consists mainly of hydroxyapatite. This is an inorganic material similar in structure to marble and hard as stone. Bacteria cannot feed on this.

Beneath the enamel, however, is the tooth bone (also called dentine). Since the dentin consists partly of organic material, it represents a potential food source for bacteria.

To simplify an example:

Humans or animals cannot eat inorganic materials such as stones because they offer no nutritional value to the organism. The same applies to the bacteria in the oral cavity, which literally "bite their teeth" on the inorganic tooth enamel.

Organic materials such as bread, cheese, meat or plants, on the other hand, can be broken down and digested by enzymes into their nutritious components. In the case of bacteria, this is the case with dentin (inorganic vs. organic | enamel vs. dentin).

But how do the harmful bacteria in the oral cavity get to the nutritious dentine?

If plaque is not removed by thorough brushing, the plaque on the tooth enamel initially provides a breeding ground for bacteria. Just like humans, bacteria metabolize their food and excrete harmful toxins in the process. The main cause of caries is the bacterium "Streptococcus mutans", which produces an acidic toxin. This acid attacks the enamel and dissolves it bit by bit. After a while, small cracks appear in the tooth enamel.


If you squeeze a lemon on a marble slab several times a day for over 20 years, you will see that the marble does not shatter, but develops small cracks.

The bacteria can then penetrate through these very cracks to the dentin – their food source. As time goes on, they cause steadily growing caries below the visible enamel. The dentist can only see caries with the naked eye when the enamel has broken through to the chewing surface. In order to be able to detect caries in the early stages (often in the space between the teeth), the dentist takes x-rays. In the pictures, the dissolved tooth enamel and the "eroded dentine" are visible as grey-black spots and cavities (see below / caries in the early stages).

There are two stages of tooth decay:

  1. Initialkaries (Karies im Anfangsstadium): Hierbei ist nur der Zahnschmelz befallen.
  2. Karies: Hier sind sowohl der Zahnschmelz als auch das Dentin befallen.

Initial caries can heal because it has only penetrated the enamel and not the dentin. However, good dental hygiene and regular fluoridation are essential for the healing process. If the caries has already arrived in the dentin, unfortunately only the drill can help.

What are signs of tooth decay and how can

you recognize tooth decay?

In the early stages, tooth decay does not cause pain or problems. And since the initial caries mainly occurs in the space between the teeth - i.e. where the teeth are brushed irregularly or not at all - it can only be recognized by the dentist through an X-ray image. If the caries is more advanced, the bacteria penetrate in the direction of the nerves that are inside the tooth. This can then lead to inflammation (pulpitis) of the nerves, which causes pain for the patient. The tooth affected by caries reacts sensitively to external influences such as heat, cold or pressure and is noticeable by an unpleasant pulling.

What can you do to avoid or prevent tooth decay?

In order to prevent the development of tooth decay, the breeding ground for the bacteria must be withdrawn. It is therefore absolutely necessary to remove the plaque on which the bacteria feed. And that is only possible mechanically, i.e. with the help of toothbrushes, interdental brushes and dental floss. In addition to removing plaque, it makes sense to use a toothpaste containing fluoride. The fluoride contained in the toothpaste is absorbed by the tooth enamel and can thus make minor repairs to the damaged enamel. The strengthened surface is therefore less susceptible to being dissolved by the acids of the bacteria.

What influence does sugar have on the
development of tooth decay?

Many patients believe that sugar is the cause of tooth decay, but this is not entirely true. In principle, sugar is only a co-factor that promotes the development of tooth decay. Although bacteria can process sugar very well, they are only present in small numbers if you clean regularly and thoroughly. Because the less plaque there is on the tooth surface, the fewer bacteria there are that can metabolize this sugar. Due to the lower number of bacteria present, less acid is excreted, which can attack the tooth enamel. This reduces the development of tooth decay. A lack of dental care between the teeth is often the cause of the development of caries. Interdental brushes are important to prevent tooth decay in this area.

What rules should you follow regarding your diet and when to brush your teeth to avoid tooth decay


A balanced and low-sugar diet makes an important contribution to preventing tooth decay.


When it comes to sugar intake, it helps to limit the “sugar shock” to a short period of time. A permanent sugar intake is disadvantageous.
This means: it is better to snack for 15-20 minutes at a time (short sugar shock) than to consume sugary drinks (sodas, cola) or sweets throughout the day.


Make sure you allow at least 30 minutes between consuming acidic drinks, such as spritzers, fruit juice, etc., and brushing your teeth (using a toothbrush, tufted brush, interdental brush, dental floss). In this way, your salivation can neutralize the acid film and you do not "clean" away the tooth enamel that has been dissolved by the acids.

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