In humans, the first attachment of the teeth takes place in the form of milk teeth. For reasons of space this contains only 20 milk teeth. As the jaw grows, it is gradually replaced.
The teeth are then changed. The teeth are placed as so-called diphydontia – double dentition. It is therefore distinguished between two generations. The first one is the development of the dentes decidui, the milk teeth. The second generation is formed by the permanent dentes, the permanent teeth.
Development of the milk tooth
The development of the milk tooth begins already in the sixth week of development, i.e. still in the womb. This is a continuous process that takes place in different stages. In the sixth week of development a U-shaped tooth strip (dentogingival strip) is formed, which grows into the connective tissue of the upper and lower jaw.
In the eighth week of development, ten tooth buds are formed from the upper and lower ridge. Each one forms the attachment of a milk tooth. The embryonic connective tissue (mesenchyme) grows into the tooth bud.
This area is called the tooth papilla. The tooth bud is now called the enamel organ, since it also produces the enamel forming agents. The inner and outer cells form the inner and outer enamel layer.
The tissue in between is called enamel pulp. The mesenchyme, which still surrounds everything, forms the tooth sac. Now the different types of cells can differentiate, from which finally the milk tooth emerges.
From the cells of the inner enamel layer the adamantoblasts, the enamel formers, develop. They release enamel proteins, from which apatite crystals are formed by the incorporation of calcium. The crystals arrange themselves into enamel prisms and thus form the tooth enamel.
When the enamel reaches a certain thickness, the adamantoblasts are transformed so that the enamel cuticle (cuticle dentis) is formed. After the eruption of the milk tooth, this cuticle is gradually rubbed off by chewing and grinding the food. However, the loss of adamantoblasts prevents the enamel from being replicated.
Damage caused by caries, for example, is therefore irreparable. The mesenchyme of the dental papilla differentiates into odontoblasts. They are the tooth formers.
They contain a lot of potassium, calcium and phosphates and release the uncalcified predentine, which is mineralized to form dentin. In addition, it is also retained as a thin layer of predentine between the dentine and the odontoblasts and can provide a constant supply of dentine due to the constant supply of minerals. The dentine of the milk tooth is thus regenerated throughout its life – in contrast to the enamel.
Many nerve fibres in small dentine tubules cause a sensation of pain when damaged. In addition to dentin and enamel are also formed: The dental pulp, which develops from the mesenchymal cells of the tooth papilla, contains nerves and vessels for supply. The Membrana preformativa, a thin basal membrane, is located between the inner enamel layer and the surface of the tooth pulp.
Finally, after the hard substances of the later deciduous tooth crown (dentin and enamel) have formed, the tooth root is formed. It is also formed by the odontoblasts and also consists of dentin. In addition, the cells from the external tooth sac develop into cementoblasts, which attach themselves to the dentine of the tooth root. They are the precursors of the cement. The alveolar bone is then formed from the cells of the deciduous tooth sac and the periodontium, the root canal skin of the tooth.
