Cementum's a specialized calcified substance covering the root of a tooth. Cementum's excreted by cells called cementoblasts within the root of the tooth and's thickest at the root apex. Its coloration's yellowish and it's softer than enamel and dentin due to being less mineralized. Cementum's main role's to anchor the tooth by attaching it via the periodontal ligaments. It also plays an important role in forming new teeth. Hence, its bottom surface's tangent to the periodontal ligaments runni… (More on Cementum)