Dentin (American English) or dentine (British English) 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 weight, 70% of dentin consists of the mineral hydroxylapatite, 20% is organic material, and 10% 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. Dentinal sclerosis/transparent dentin-sclerosis of primary dentin is regressive alteration in tooth characterized by calcification of dentinal tubules. It can occur as a result of injury to dentin by caries or abrasion, also manifestation of normal aging process.