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Dentin
Dentin (/ˈdɛntɪn/ DEN-tin) (American English) or dentine (/ˈdɛnˌtiːn/ DEN-teen or /ˌdɛnˈtiːn/ DEN-TEEN) (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 and can become hypersensitive to changes in temperature due to the sensory function of odontoblasts, especially when enamel recedes and dentin channels become exposed.
Prior to enamel formation, dentin formation begins through a process known as dentinogenesis, and this process continues throughout a person's life even after the tooth has fully developed. Events such as tooth decay and tooth wear can also initiate dentin formation.
Dentinogenesis is initiated by the odontoblasts of the pulp. Odontoblasts are specialised cells that lay down an organic matrix known as pre-dentin. This predentin is subsequently mineralized into dentin. Mineralization of predentin begins at the dentinoenamel junction during tooth development and progresses towards the pulp of the tooth. After growth of predentin and maturation into dentin, the cell bodies of the odontoblasts remain in the pulp, along its outer wall, and project into tiny tubules in the dentin.
Predentin 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 mineralized into dentin. See the Structure section for information about the composition of dentin.
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. Tapering from the inner to the outermost surface, they have a diameter of 2.5 μm near the pulp, 1.2 μm in the middle of the dentin, and 0.9 μm at the dentinoenamel junction. Their density is 59,000 to 76,000 per square millimeter near the pulp, whereas the density is only half as much near the enamel.[citation needed] Within the tubules, there is an odontoblast process, which is an extension of an odontoblast, and dentinal fluid, which contains a mixture of albumin, transferrin, tenascin and proteoglycans. In addition, there are branching canalicular systems that connect to each other. These branches have been categorized by size, with major being 500–1000 nm in diameter, fine being 300–700 nm, and micro being less than 300 nm. The major branches are the terminal ends of the tubules. About every 1-2 μm, there are fine branches diverging from dentinal tubules at 45 degree angles. The microtubules diverge at 90 degree angles. The dentinal tubules contain the cytoplasmic extensions of odontoblasts that once formed the dentin and maintain it. The cell bodies of the odontoblasts are aligned along the inner aspect of dentin against a layer of predentin where they also form the peripheral boundary of the dental pulp Because of dentinal tubules, dentin has a degree of permeability, which can increase the sensation of pain and the rate of tooth decay. The strongest held theory of dentinal hypersensitivity suggests that it is due to changes in the dentinal fluid associated with the processes, possibly 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 less mineralized 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 during tooth preparation.
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.
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.") The dentinal tubules in this region branch profusely.
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Dentin
Dentin (/ˈdɛntɪn/ DEN-tin) (American English) or dentine (/ˈdɛnˌtiːn/ DEN-teen or /ˌdɛnˈtiːn/ DEN-TEEN) (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 and can become hypersensitive to changes in temperature due to the sensory function of odontoblasts, especially when enamel recedes and dentin channels become exposed.
Prior to enamel formation, dentin formation begins through a process known as dentinogenesis, and this process continues throughout a person's life even after the tooth has fully developed. Events such as tooth decay and tooth wear can also initiate dentin formation.
Dentinogenesis is initiated by the odontoblasts of the pulp. Odontoblasts are specialised cells that lay down an organic matrix known as pre-dentin. This predentin is subsequently mineralized into dentin. Mineralization of predentin begins at the dentinoenamel junction during tooth development and progresses towards the pulp of the tooth. After growth of predentin and maturation into dentin, the cell bodies of the odontoblasts remain in the pulp, along its outer wall, and project into tiny tubules in the dentin.
Predentin 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 mineralized into dentin. See the Structure section for information about the composition of dentin.
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. Tapering from the inner to the outermost surface, they have a diameter of 2.5 μm near the pulp, 1.2 μm in the middle of the dentin, and 0.9 μm at the dentinoenamel junction. Their density is 59,000 to 76,000 per square millimeter near the pulp, whereas the density is only half as much near the enamel.[citation needed] Within the tubules, there is an odontoblast process, which is an extension of an odontoblast, and dentinal fluid, which contains a mixture of albumin, transferrin, tenascin and proteoglycans. In addition, there are branching canalicular systems that connect to each other. These branches have been categorized by size, with major being 500–1000 nm in diameter, fine being 300–700 nm, and micro being less than 300 nm. The major branches are the terminal ends of the tubules. About every 1-2 μm, there are fine branches diverging from dentinal tubules at 45 degree angles. The microtubules diverge at 90 degree angles. The dentinal tubules contain the cytoplasmic extensions of odontoblasts that once formed the dentin and maintain it. The cell bodies of the odontoblasts are aligned along the inner aspect of dentin against a layer of predentin where they also form the peripheral boundary of the dental pulp Because of dentinal tubules, dentin has a degree of permeability, which can increase the sensation of pain and the rate of tooth decay. The strongest held theory of dentinal hypersensitivity suggests that it is due to changes in the dentinal fluid associated with the processes, possibly 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 less mineralized 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 during tooth preparation.
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.
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.") The dentinal tubules in this region branch profusely.