Events such as tooth decay and tooth wear can also initiate dentine formation.Dentinogenesis is initiated by the odontoblasts of the pulp. Odontoblasts are specialised cells that lay down an organic matrix known as pre-dentine. This pre-dentine is subsequently mineralised into dentine. Mineralisation of pre-dentine begins at the dentino-enamel junction during tooth development and progresses towards the pulp of the tooth. After growth of pre-dentine and maturation into dentine, the cell bodies of the odontoblasts remain in the pulp, along its outer wall, and project into tiny tubules in the dentine. Pre-dentine is composed of 90% type I collagen and 10% non-collagenous proteins (including phosphoproteins, proteoglycans, growth factors, phosphatases such as alkaline phosphatase, and matrix metalloproteinases (MMPs)), and this composition is significantly altered when it is mineralised into dentine. See the Structure section for information about the composition of dentine. Structure
Unlike enamel, dentin may be demineralized and stained for histological study. Dentin consists of microscopic channels, called dentinal tubules, which radiate outward through the dentin from the pulp to the exterior cementum or enamel border. The dentinal tubules extend from the dentinoenamel junction (DEJ) in the crown area, or dentinocemental junction (DCJ) in the root area, to the outer wall of the pulp. From the outer surface of the dentin to the area nearest the pulp, these tubules follow an S-shaped path. The diameter and density of the tubules are greatest near the pulp.
Dentin () (American English) or dentine ( or ) (British English) (Latin: substantia eburnea) is a calcified tissue of the body and, along with enamel, cementum, and pulp, is one of the four major components of teeth. It is usually covered by enamel on the crown and cementum on the root and surrounds the entire pulp. By volume, 45% of dentin consists of the mineral hydroxyapatite, 33% is organic material, and 22% is water. Yellow in appearance, it greatly affects the color of a tooth due to the translucency of enamel. Dentin, which is less mineralized and less brittle than enamel, is necessary for the support of enamel. Dentin rates approximately 3 on the Mohs scale of mineral hardness. There are two main characteristics which distinguish dentin from enamel: firstly, dentin forms throughout life; secondly, dentin is sensitive: 125  and can become hypersensitive to changes in temperature due to the sensory function of odontoblasts, especially when enamel recedes and dentin channels become exposed. Dentinal sclerosis
Dentinal sclerosis or transparent dentin sclerosis of primary dentin is a change in the structure of teeth characterized by calcification of dentinal tubules. It can occur as a result of injury to dentin by caries or abrasion, or as part of the normal aging process. Development
Prior to enamel formation, dentine formation begins through a process known as dentinogenesis, and this process continues throughout a persons life even after the tooth has fully developed.