Editing Dentin (section)

=== Regional variations in dentin structure and composition ===

The different regions in dentin can be recognized due to their structural differences. The outermost layer, known as the mantle dentin layer, is found in the crown of the tooth. It can be identified by the presence of various characteristics, including collagen fibres found perpendicular to the enamel-dentin junction and it is slightly less mineralized (by approximately 5%, compared to the enamel. The dentin undergoes mineralization in the presence of matrix vesicles ("hydroxyapatite-containing, membrane-enclosed vesicles secreted by odontoblasts, osteoblasts, and some chondrocytes; believed to serve as nucleation centers for the mineralization process in dentin, bone, and calcified cartilage.")<ref>{{cite web | url = https://medical-dictionary.thefreedictionary.com/matrix+vesicles | title = Matrix vesicles | date = 2012 | work = Farlex Partner Medical Dictionary | publisher = Farlex }}</ref> The dentinal tubules in this region branch profusely.

In the root of the tooth there are two morphologically distinguishable outer layers: the hyaline layer on the periphery of dentin and Tomes granular layer beneath this. The granular layer has a dark, granular appearance which occurs due to the branching and looping back of dentinal tubules in this region. This appearance, specific to root dentin, is possibly due to differences in the rates of formation of coronal and root dentin. The hyaline layer, which has an obscure origin, is a clear layer, unlike the granular layer, with a width of up to 20μm. It can have clinical significance during periodontal regeneration.

Circumpulpal dentin forms the majority of the dentin and is generally constant in structure. Peripherally, mineralization can be seen to be incomplete, whereas centrally the mineralizing front shows ongoing mineralizing.

The innermost layer of dentin is known as predentin, and is the initial dentin matrix that is laid down prior to mineralization. It can be distinguished by its pale color when stained with haematoxylin and eosin. The presence of odontoblastic processes here allows the secretion of matrix components. Predentin can be 10-40μm in width, depending on its rate of deposition.<ref name = "Berkovits_2002" />{{rp|134–137}}