Periodontology Anatomy - Cementum

Cementum is a special type of calcified substance which covers the root of a tooth. The cementum is the portion of the periodontium which attaches the teeth to the alveolar bone through anchoring of the periodontal ligament.

Structure

The cells of the cementum are the entrapped cementoblasts or the cementocytes. Each cementocyte lies in its lacuna, which is similar to the pattern noted in the bone. These lacunae also contain canaliculi or canals. However, unlike the canals found in bone, the canals in cementum do not contain nerves and do not radiate outward. The canals orient towards the periodontal ligament and contain cementocytic processes which exist in order to diffuse nutrients from the vascularized ligament.

After the apposition of cementum in layers, the cementoblasts which are not entrapped in cementum line the cemental surface along the length of the outer covering of the periodontal ligament. These cementoblasts are able to form subsequent layers of cementum if the tooth suffers from trauma or injury.

Sharpey fibers are also part of the principal collagenous fibers of the periodontal ligament which are embedded in the cementum and alveolar bone. They help in attaching the tooth to the alveolus.

If cementum is visible on the teeth, it can suggest that the roots are exposed. This shows that the clinical crown or exposed part of the tooth, is bigger than the surface of the tooth that is covered by enamel. This is often a result of gingival recession and indicate the presence of periodontal disease.

Cementoenamel junction

The cementum then joins the enamel and forms the cementoenamel junction (CEJ). This junction is referred to as the cervical line.

Three possible types of transitional interfaces can be present at the CEJ. The traditional view was that certain interfaces were dominant in certain oral cavities. The CEJ may exhibit all of these different interfaces in the oral cavity. There can even be considerable variation when one tooth is traced circumferentially.

Dentinocemental junction

When the cementoid reaches the necessary thickness, the cementoid which surrounds the cementocytes becomes mineralized. It is then considered to be cementum. Because of the apposition of cementum over the dentin, the dentinocemental junction (DCJ) is ultimately formed. This interface is not as defined compared to the dentinoenamel junction (DEJ). The dentinocemental junction (DCJ) is a relatively smooth area found in permanent teeth.

Types

The different types of cementum are based on the presence or absence of cementocytes. In addition, the types are determined whether the collagen fibers are extrinsic or intrinsic. While fibroblasts and some cementoblasts secrete extrinsic fibers, only cementoblasts secrete intrinsic fibers. The extrinsic fibers contained in acellular extrinsic fiber cementum, travel perpendicular to the surface of the root. This allows the tooth to attach to the alveolar bone by the periodontal ligament (PDL) and continuously with the cementodentinal junction (CDJ). Acellular cementum contains only extrinsic collagen fibers. In comparison, cellular cementum is thicker and contains both extrinsic and intrinsic collagen fibers. The first cementum which is formed during the tooth’s development is acellular extrinsic fiber cementum. The acellular layer of cementum is living tissue which does not incorporate cells into its structure and usually predominates on the coronal half of the root.