there are 2 layers of dentine – what lies between
Dentin Dentin (/ˈdɛntɪn/) (American English) or dentine (/ˈdɛnˌtiːn/ or /ˌdɛnˈtiːn/) (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 hydroxylapatite, 33% is organic material, and 22% is water.[1] 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.[2] Dentin rates approximately 3 on the Mohs scale of mineral hardness.[3] There are two main characteristics which distinguish dentine from enamel; firstly dentine forms throughout life, and secondly, dentine is sensitive. [4]