Dentin (dentine) is the substance between the 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 it still acts as a protective layer and supports the crown of the tooth.
Dentin is a mineralized connective tissue with an organic matrix of collagenous proteins. The inorganic component of dentine consists of dahllite. Dentin contains a microscopic structure called dentinal tubules which are micro-canals that radiate outward through the dentine from the pulp cavity to the exterior cementum border. These canals have different configurations in different ivories and their diameter ranges between 0.8 and 2.2 micrometres. 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.
Dentin is also the hard material that makes up shark scales. Basically, the scales are tiny teeth. They all point backward, so stroking it from head to tail produces a smooth feeling however, stroking the skin in the opposite direction reveals a rough texture. Studies have found that the dentin scales act as armor for a shark and also create tiny vortices that reduce drag to make them faster. The scales also allow sharks to swim silently compared to other fish that generate considerable noise when they ply the water.
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