The strongest held theory of dentinal hypersensitivity suggests that it is due to changes in the dentinal fluid associated with the processes, a type of hydrodynamic mechanism.Dentin is a bone-like matrix that is porous and yellow-hued material. It is made up, by weight, of 70-72% inorganic materials (mainly hydroxylapatite and some non-crystalline amorphous calcium phosphate), 20% organic materials (90% of which is collagen type 1 and the remaining 10% ground substance, which includes dentin-specific proteins), and 8-10% water (which is adsorbed on the surface of the minerals or between the crystals). Because it is softer than enamel, it decays more rapidly and is subject to severe cavities if not properly treated, but due to its elastic properties, it is good support for enamel. Its flexibility prevents the brittle enamel fracturing. In areas where both primary and secondary mineralization have occurred with complete crystalline fusion, these appear as lighter rounded areas on a stained section of dentin and are considered globular dentin. In contrast, the darker arc-like areas in a stained section of dentin are considered interglobular dentin. In these areas, only primary mineralization has occurred within the predentin, and the globules of dentin do not fuse completely. Thus, interglobular dentin is slightly less mineralized than globular dentin. Interglobular dentin is especially evident in coronal dentin, near the dentinoenamel junction (DEJ), and in certain dental anomalies, such as in dentinogenesis imperfecta. Regional variations in dentin structure and composition
The different regions in dentin can be recognized due to their structural differences.
Secondary dentin
Secondary dentin (adventitious dentin) is formed after root formation is complete, normally after the tooth has erupted and is functional. It grows much more slowly than primary dentin but maintains its incremental aspect of growth. It has a similar structure to primary dentin, although its deposition is not always even around the pulp chamber. It appears greater in amounts on the roof and floor of the coronal pulp chamber, where it protects the pulp from exposure in older teeth. The secondary dentin formed is not in response to any external stimuli, and it appears very much similar to the primary dentine. It is the growth of this dentin that causes a decrease in the size of the pulp chamber with age. This is clinically known as pulp recession; cavity preparation in young patients, therefore, carries a greater risk of exposing the pulp. If this occurs, the pulp can be treated by different therapies such as direct pulp capping. Previously it was thought that Pulp capping was most successful if followed by a stainless steel crown, however this procedure is most of the times unnecessary in children. it requires the unnecessary removal of enamel which is key to the life of the tooth. Adhesive dentistry allows for conservative restoration techniques that minimize the loss of tooth structure and should be used. In order to maintain space in the primary dentition, attempts are made not to extract a pulpal exposure.