The cementum (substantia ossea) is the third hard tissue of the tooth. Periodically secreted by specialized cells (cementoblasts) in the periodontal membrane, the cementum is a coarse material which binds and anchors the tooth to the periodontal ~ligament~. The cementum is composed of about 50% organic tissue, with the rest being water and inorganic (mostly calcium) salts. If the periodontal membrane is damaged, the cementum may be resorbed back into the membrane.
