The cementum is a special type of calcified substance which covers and protects tooth’s root. The cementum is part of the periodontium which is used to attach the teeth to the alveolar bone by anchoring the periodontal ligament.
The cells of the cementum are the entrapped cementoblasts and cementocytes. Each cementocyte is in its lacuna, which is similar to the pattern found of the bone. The lacunae also contain canals or canaliculi. Unlike the canals found in the bone, the canals of the cementum do not do not radiate outward or contain nerves. The canals in the lacunae orient towards the periodontal ligament and contain cementocytic processes. These processes exist in order to diffuse the necessary nutrients from the vascularized ligament.
The cementoblasts, which are not entrapped in the cementum, line the cemental surface over the length of the outer covering of the periodontal ligament. These cementoblasts are able to form subsequent layers of cementum when the teeth experience injury or trauma.
Sharpey fibers are part of the principal collagenous fibers of the periodontal ligament which are embedded in the cementum and alveolar bone. They are used to attach the tooth to the alveolus.
If the cementum is visible on the teeth, it can suggest that roots are exposed. This demonstrates that the exposed part of the tooth is larger than the surface of the tooth covered by the enamel. This is often the result of gingival recession and an early indicator of periodontal disease.
The cementum attaches to the enamel to form the cementoenamel junction (CEJ) which is called the cervical line.
There are three possible types of transitional interfaces which can exist at the CEJ. The traditional view point was that specific interfaces dominated in certain oral cavities. The CEJ may exhibit each of these various interfaces in the oral cavity. When one tooth is traced circumferentially, there can be a substantial variation.
The differing types of cementum are based on the presence or lack thereof of cementocytes. In addition, the types of cementum are determined based on if the collagen fibers are extrinsic or intrinsic. While fibroblasts and some cementoblasts secrete extrinsic fibers, only cementoblasts are found to secrete intrinsic fibers. The extrinsic fibers contained in acellular extrinsic fiber cementum, travel perpendicular to the root surface. This allows the tooth to attach to the alveolar bone through the periodontal ligament (PDL) and continuously with the cementodentinal junction (CDJ). Acellular cementum exclusively contains extrinsic collagen fibers. In contrast, the cellular cementum is thicker and contains both extrinsic and intrinsic collagen fibers. The first cementum, formed during the development of the tooth, is acellular extrinsic fiber cementum. The acellular layer of the cementum is live tissue which does not incorporate cells into its structure. It usually predominates on the coronal half of the root.
The cementum is slightly softer than the dentin and consists of approximately 45-50% inorganic material (hydroxylapatite) by weight. In addition, it consists of about 50-55% organic matter and water by weight. The organic portion of the material is primarily composed of collagen and proteoglycans. Cementum is avascular, meaning it receives its nutrition through imbedded cells from the surrounding vascular periodontal ligament.
The cementum is light yellow in color and contains the highest amount of fluoride content of all mineralized tissue. Cementum is also permeable to various materials. It continuously forms throughout a patient’s life because a new layer of cementum is deposited in order to keep the attachment intact as the superficial layer of the cementum ages.