A tooth consists of three mineralized tissues,enamel,dentin,and cementum,and a dental pulp.The enamel is of ectodermal origin while the other components are of mesenchymal origin.The enamel consists of millions of rods,or prisms,which extend from the amelodentinal junction to the surface of the crown.Each rod is composed of apatite crystals,mainly hydroxyapatite,and is optically separated from adjacent rods by a rod sheath,or cortex.The existence and nature of the rod sheath is controversial.Some believe that the appearance is due to the presence of a higher content of organic material,while others believe that differences in crystal orientation of adjacent rods in this zone,with resultant differences in light refraction,cause an optical illusion seen as a sheath.These views are probably reconcilable.

    Teeth can be divided into 3 parts in appearance,including dental crown,dental neck and teeth root.Dental crown is the visible part.There are dental neck and teeth root ensconced in gums and alveolar bone.Teeth root is so long and might be beyond your imagination.Teeth can be divided into 4 parts in structure,including tooth enamel,dentin,cementum and dental pulp.

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