Its main functions are attaching the periodontal ligament fibers to the root surface and root surface repair. Both types of cementum are produced by cementoblast cells. Cementum is laid out initially as a layer of uncalcified tissue known as cementoid which later becomes calcified. In case of acellular cementum the cells remain on the outer surface and in case of cellular cementum they are trapped within the cementum and become cementocytes. Cementocytes dwell in lacunae and connect together by cytoplasmic processes extending through a system of interconnected canals within the cementum.
Cellular cementum is usually present in the apical third of the root.
Cementum increases in thickness throughout the life of the tooth by periodic apposition in response to functional demand. Layers of cementum are demarcated by incremental lines. The parts of the periodontal ligament fibers and the gingival fibers which are lodged into the cementum are called Sharpey's fibers. They are positioned perpendicularly on the root surface and form the extrinsic fiber system. Another group of fibers within the cementum circle the tooth to form the intrinsic fiber system.