General Dentistry Concepts: Dentin
Dentin is a calcified tissue of the body. Dentin, enamel, cementum and pulp, are the four major components that make up the teeth. It is often covered by enamel on the crown and cementum of the root and surrounds the tooth’s pulp. Dentin is comprised of 45% hydroxylapatite, 33% organic material and 22% water. Dentin is yellow in its appearance and greatly affects the tooth’s color because of the enamel’s translucency. Dentin is less mineralized and less brittle in comparison to enamel. It is also necessary for the support of the enamel. Dentin has a score of 3 on the Mohs scale of mineral hardness. Dentin forms throughout life and is very sensitive.
Dentinal sclerosis or transparent dentin-sclerosis of primary dentin is the regressive alteration in teeth caused by the calcification of the dentinal tubules. It can occur as a result of cavities, an abrasion or as part of the normal aging process.
The formation of dentin begins prior to the formation of the enamel. Dentin formation is initiated by the odontoblasts of the pulp. Dentin comes from the dental papilla of the tooth germ. Unlike enamel, dentin forms throughout your life. The growth of dentin can be initiated from stimuli, such as tooth decay or attrition.
Dentin, unlike enamel, can be demineralized and stained for histological study. Dentin contains microscopic channels, which are called dentinal tubules, which radiate outward through the dentine from the pulp to the enamel border. The dentinal tubules extend from the dentinoenamel junction which is located in the crown area or dentinocemental junction in the root area, towards the outer wall of the pulp. From the outer surface of the dentin to the area closest to the pulp, these tubules create an S-shaped path. The tubules near the pulp has the greatest diameter and density. Because of dentinal tubules, dentin is permeable, which can increase the pain sensitivity in addition to the rate of tooth decay.
There are three different types of dentin which include primary, secondary and tertiary. Secondary dentin is a layer of dentin which is produced after the tooth’s root is completely formed. Tertiary dentin is created in response to a stimulus, such the presence of tooth decay or wear.
Primary dentin is the most prominent form of dentin within the tooth. It is located between the enamel and the pulp chamber. The outer layer of dentist which is closest to the enamel is referred to as mantle dentin. This layer of dentin is unique to the rest of primary dentin. Mantle dentin is formed by newly differentiated odontoblasts and forms a layer that is typically 15-20 micrometers (µm) wide.
Secondary dentin or adventitious dentin is formed following the formation of the root. Secondary dentin typically forms after the tooth has erupted and is fully functional. It grows at a much slower rate compared to primary dentin but maintains its incremental aspect of growth. It has a similar structure to the primary dentin. Its deposition is not consistently even around the pulp chamber.
Tertiary dentin is dentin formed from a reaction to external stimulation. This stimulation can include cavities and regular wear. It is either reactionary or reparative.