Dentin
From Wikipedia, the free encyclopedia
Dentin (BE: dentine) is the substance between enamel (substance in the crown) or cementum (substance in the root) of a tooth and the pulp chamber. Dentin is secreted by the odontoblasts of the dental pulp. The formation of dentin is known as dentinogenesis. The porous, yellow-hued material is made up of 70% inorganic materials, 20% organic materials, and 10% water. Because it is softer than enamel, it decays more rapidly and is subject to severe cavities if not properly treated, but dentin still acts as a protective layer and supports the crown of the tooth.
Elephant ivory is solid dentin. The structure of the dentinal tubules contributes both to its porosity (useful for piano keys) and its elasticity (useful for billiard balls.) Elephant tusks are formed with a thin cap of enamel, which soon wears away, leaving the dentin exposed. Exposed dentin in humans causes the symptom of sensitive teeth.
Dentin is a mineralized connective tissue with an organic matrix of collagenous proteins. The inorganic component of dentin consists of dahllite. Dentin has a complex structure. Microscopic channels called dentinal tubules radiate outward through the dentin from the pulp cavity to the exterior cementum or enamel border. These canals have different configurations in different species and their diameter ranges between 0.8 and 2.2 micrometres. Although they may have tiny side-branches, they do not intersect with each other. Their length is dictated by the radius of the tooth. The three dimensional configuration of the dentinal tubules is under genetic control and is therefore a characteristic unique to the order, although in many mammalian species the tubules follow a gentle helical course through the solid matrix.
Because dentin is softer than enamel, it wears away more quickly than enamel. Some mammalian teeth exploit this phenomenon, especially herbivores such as horses, deer or elephants. In many herbivores, the occlusal (biting) surface of the tooth is composed of alternating areas of dentin and enamel. Differential wearing causes sharp ridges of enamel to be formed on the surface of the tooth (typically a molar), and to remain during the working life of the tooth. Herbivores grind their molars together as they chew (masticate), and the ridges help to shred tough plant material.
Dentin may be demineralised and stained for histological study, unlike enamel. Dentin rates approximately 3 on the Mohs scale of mineral hardness.
A material similar to dentin forms the hard material that makes up dermal denticles in sharks and other cartilaginous fish.
