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. The principal role of cementen within the tooth is to serve as a medium by which the periodontal ligaments can attach to the tooth for stability. Hence, its bottom surface is tangent to the periodontal ligament… (More on Cementum)