Cementum is a specialized calcified substance covering the root of a tooth. Cementum is excreted by cells called cementoblasts within the root of the tooth and is thickest at the root apex. Its coloration is yellowish and it's softer than enamel and dentin due to being less mineralized. Cementum's main role is 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 is tangent to the periodontal ligaments… (More on Cementum)