Dentin or dentine is a layer of material that lies immediately underneath the enamel of the tooth. It is one of the four major components of the tooth which comprises:
The outer hard enamel
The dentin underneath the enamel
The dental pulp that lies soft and encased within the dentin
The cementum that lies over the dentin and helps attach the tooth to the jaw
Development of dentin
The dentin is formed from the odontoblasts that are present in the outermost layer of the dental pulp. The odontoblasts first form predentin which then matures into dentin. Unlike the enamel, dentin is regenerative and is replaced if it becomes worn out or decayed.
Structure of the dentin
The dentin is covered by the enamel at the crown of the tooth, the portion that is visible in the mouth. At the root, the dentin is covered by the cementum. The mineral hydroxyapatite makes up around 70% of the dentin, while 20% is organic matter and 10% water. It is yellow and looks much like the tooth enamel. However, since enamel is nearly transparent, it is the dentin that is thought to give colour to the tooth.
Within the dentin lie microscopic channels called the dentinal tubules. These are aligned in a radial pattern around the pulp, extending outwards from the pulp towards the outer enamel at the crown of the tooth and towards the cementum in the root of the tooth. The dentinal tubules contain cells and fluid. This gives the dentin a degree of permeability which can increase painful sensations and accelerate the progression of tooth decay.
There are three types of dentin, which are defined by the location of the dentin. The outermost part is called the primary dentin and is the dentin that is in contact with the enamel. The region of dentin in the root that is in contact with the cementum is called the secondary dentin. Tertiary dentin is dentin that is formed in response to tooth decay.
Functions of the dentin
Overall, the dentin contains less minerals and is less brittle or breakable than the enamel. Its main function is to provide support to the enamel. It is also responsible for transmitting impulses from the enamel or root to the dental pulp.