Cementum

Root cementum is visible as a tiny, slightly basophilic layer at the outer surface of the root part of the tooth and can be distinguished from dentin by the absence of tubuli. It obliterates the peripheral ends of the dentinal tubuli and lies adjacent to the mantle dentin. It is the product of fibroblasts from the dental follicle migrating to the root surface and differentiating into cementoblasts. Whether epithelial cells from Hertwig’s sheath contribute to initial cementum formation is controversial as has already been discussed.

Over the course of time, cells from the periodontal ligament may add new cemental layers to the root surface in which cells may become entrapped. Te cellular cementum formed 
in this way closely resembles bone and can only be identified as cementum by its location: covering a root surface. Deposition of cementum probably continues throughout life. It is superimposed upon the cementum that is formed initially during tooth formation. Collagen fibers from the periodontal ligament are embedded in the cementum, thus ensuring fixation of the tooth in its socket. Coronally, cementum ends where enamel starts. Usually, there is a slight overlap, cementum covering the cervical enamel over a short distance. However, an edge-to-edge border as well as a tiny gap between both tooth covering tissues may also be seen.