The human dentition contains 28 teeth in adults, with wisdom teeth it is 32. The shape of the teeth varies according to their position. Incisors are somewhat narrower, molars are more massive, depending on their function. The structure, i.e. what the tooth consists of, is the same for every tooth and person. The hardest substance of the whole body is in our mouth, but once lost it will not come back.
The outer structure
Viewed from the outside, the tooth can first be divided into three sections. The last two are overgrown by the gum. The ratio of crown to root is about 1/3 to 2/3.
The tooth consists of such a hard substance because it is exposed to strong forces every day, which we do not perceive as such when chewing. It has to withstand a daily load of 15-30kg, in extreme cases it can even be 100kg. In order to be able to do this, it is made up of different substances, which will be discussed in the following sections.
The main substance of the tooth is the dentin, which is overlaid by the so-called enamel at the neck and crown of the tooth. In the root area, however, the enamel is no longer present. There the dentin is covered by the root cement.
The transition from enamel to root cement is at the neck of the tooth. The inside of the tooth consists of the pulp cavity, the supply center of the tooth.
- The visible part that protrudes from the gums is the crown.
- The neck of the tooth is attached to it,
- This represents the transition to the tooth root, which is firmly anchored in the alveolar socket.
The internal structure
If you explore the tooth from the inside out, you will first encounter the pulp. This is, as mentioned above, the supply center of the teeth. Its tasks are nutrition, sensitivity, defense and formation.
It gives the tooth its shape, nourishes it, has defensive bodies and enables it to feel. It can be divided into an inner and outer zone. On the very outside, i.e. on the border with the dentine, are the odontoblast bodies that form the dentine.
They thus line the edge of the cave from the inside. Towards the bottom, the pulp tapers to the apical foramen. The vessels and nerves that supply the tooth with nutrients pass through this foramen.
The next stop on the exploratory tour is the dentin. It consists of 70% minerals, such as calcium and phosphate, 20% organic substances, which is mainly collagen, and 10% water. Tiny tubules, the dentinal tubules, can be seen in the dentine.
They contain the tomes fibers. These are the extensions of the odontoblasts, which line the edge of the pulp cavity. The density and diameter of the tubules decrease with increasing distance from the pulp.
The dentin that lies very close to the pulp is called predentine, as it is still uncalcified. This is followed by the circumpulpal dentin, which is the main mass of dentin. Close to the enamel is the third layer, the mantle dentin.
This has many collagen fibers, is highly branched and less densely mineralized. If the dentine is cut across, certain growth lines (from Ebner lines) can be seen, which are less mineralized. Depending on when the dentin is formed, three types can be distinguished.
There is the primary dentin, which is formed during tooth development. Secondary dentin is formed after tooth root development. Tertiary dentine always develops when the tooth has been damaged by irritation, among other things.
The dentin is surrounded by enamel in the area of the crown of the tooth. This consists of 95% minerals, 4% water and 1% organic substances. The enamel is formed during development by ameloblasts and has a crystalline structure.
The individual crystallites have a hexagonal structure and are bundled together to form several. Such bundles are called melting prisms. The individual melting prisms interlock with each other.
Due to the curved shape of the prisms, the refraction of light causes a dark (diazonia) and a light (parazonia) stripe. In enamel, growth lines are called retinal stripes. The enamel itself has no metabolism.
However, a de- and remineralization still takes place, even if the ameloblasts only form enamel during development. Ions, water and colorants can pass through the enamel. The color of the enamel depends on the underlying translucent dentin.However, discolorations caused by tea, smoke, medication, etc. may occur. can influence the permeability.
