{{Short description|Hard tissue covering the tooth root}}
Cementum is a calcified avascular mesenchymal tissue that forms the outer covering of the anatomic root. It provides anchorage mainly to the principal fibers of periodontal ligament.
{{Tooth anatomy}}
[[File:Periodontium.svg|alt=|thumb|439x439px|The '''cementum''' is the surface layer of the tooth root, covering the dentine (which is labeled ''B''). Rather than being a passive entity like paint on a wall, cementum is a dynamic entity within the periodontium. It is attached to the alveolar bone ''(C)'' by the fibers of the periodontal ligament and to the soft tissue of the gingiva by the gingival fibers ''(H)''.]]
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===Fibers in Cementum===
Two sources of collagen fibers can be found in
the cementum:
#Sharpey’s (extrinsic) fibers which are formed by the fibroblasts.
[[File:Basic anatomy tooth.jpg|thumb|Basic anatomy of a tooth, showing the location of cementum.]]
#Fibers belonging to the cementum matrix per se (intrinsic) produced by cementoblasts.
[[File:Human tooth diagram-en.svg|thumb|Diagram of a human tooth, illustrating the layers including cementum.]]
[[File:Periodontium.svg|thumb|Diagram of the periodontium, highlighting the role of cementum.]]
===Types of Cementum===
'''Cementum''' is a specialized calcified substance covering the root of a tooth. It is part of the [[periodontium]], which also includes the [[gingiva]], [[periodontal ligament]], and [[alveolar bone]]. Cementum plays a crucial role in tooth support and stability by anchoring the [[periodontal ligament]] fibers to the tooth.
====Acellular cementum====
*Forms during root formation.
==Structure==
*Does not contain any cells.
Cementum is a mineralized tissue similar to bone but is avascular, meaning it lacks blood vessels. It is composed primarily of hydroxyapatite, collagen fibers, and water. Cementum is classified into two types based on the presence of cells:
*Seen at the coronal portion of root.
*Formation is slow.
*Arrangement of collagen fibers are more organized.
====Cellular cementum====
* '''Acellular cementum''': This type covers the cervical two-thirds of the root and is primarily responsible for anchoring the tooth in the socket. It does not contain cells within its structure.
* '''Cellular cementum''': Found mainly in the apical third of the root, this type contains cementocytes within lacunae. It is involved in the adaptive and reparative processes of the tooth.
*Forms after the eruption of the tooth and in response to functional demands.
==Function==
*Contains cementocytes.
Cementum serves several important functions:
*Seen at a more apical portion of root.
*Deposition is more rapid.
*Collagen fibers are irregularly arranged.
===Classification===
* '''Attachment''': It provides a medium for the attachment of the [[periodontal ligament]] fibers, which connect the tooth to the alveolar bone.
Depending on location, morphology and histological appearance, Shroeder and Page have classified cementum as:
* '''Protection''': Cementum protects the root dentin from resorption and external stimuli.
====Acellular afibrillar cementum (AAC)====
* '''Repair''': It plays a role in the repair of root surfaces following damage or resorption.
It contains only the mineralized ground substance. It does not contain collagen fibers nor does it exhibit entrapped Cemento-cytes. It is a product of cementoblasts and is found almost exclusively on the enamel near the cementoenamel junction with a thickness of 1 to 15 μm.
====Acellular extrinsic fiber cementum (AEFC)====
By definition it is composed primarily of Sharpey’s fibers of periodontal ligament but does not contain cementocytes. Developmentally they come to occupy the coronal one half of the root surface. Its thickness is between 30 and 230 μm.
====Cellular mixed stratified cementum (CMSC)====
It harbors both intrinsic (cementoblasts derived) and extrinsic (fibroblast derived) fibers and may contain cells. In
humans it is seen in the apical third of the roots, apices and furcation areas. Its thickness varies from 100 to 1000 μm.
====Cellular intrinsic fiber cementum (CIFC)====
It contains only intrinsic fibers secreted by cementoblasts and not by the periodontal ligament fibroblasts. In humans it
fills the resorption lacunae.
====Intermediate cementum (or) the hyaline layer of Hope Well Smith====
It is an ill-defined zone extending from precementoenamel junction to the apical 1/3rd of the root. It appears to contain cellular remnants of Hertwig’s Sheath embedded in calcified ground substance. The significance of this layer is that, it contains enamel like proteins, which helps in attachment of cementum to dentin. It has been observed by many that, when this
layer is removed during root planing procedure, the resultant reparative cementum that is formed will not be attached firmly on the dentin.
===Functions===
*Primary function of cementum is to provide anchorage to the tooth in its alveolus. This is achieved through the collagen fiber bundles of the periodontal ligament, whose ends are embedded in cementum.
==Development==
*Cementum also plays an important role in maintaining occlusal relationships, whenever the incisal and occlusal surfaces are abraded due to attrition, the tooth supra erupts in order to compensate for the loss and deposition of new cementum occurs at the apical root area.
Cementum formation begins during tooth development, after the formation of the root dentin. The process is initiated by the [[Hertwig's epithelial root sheath]], which induces the differentiation of dental follicle cells into cementoblasts. These cementoblasts secrete the organic matrix of cementum, which subsequently mineralizes.
===Composition===
==Clinical Significance==
The cementum is composed of both inorganic (46%) and organic matter. The organic matrix is chiefly composed of 90% Type I collagen, 5% Type III collagen and non-collagenous proteins like enamel proteins, adhesion molecules like tenascin and fibronectin, glycosaminoglycans like chondroitin sulfate, dermatan sulfate and heparan sulfate which constitute the remaining organic matrix.
Cementum is essential for maintaining tooth stability and health. Loss or damage to cementum can lead to tooth mobility and periodontal disease. Conditions such as [[cemental tears]] and [[hypercementosis]] can affect the integrity of cementum and require clinical attention.
===Thickness of Cementum===
Formation of cementum is a continuous process, the formative rate of which varies throughout life. It is most rapid at the apical regions. At the coronal half the thickness varies from 16 to 60 μm (almost the thickness of hair) and at the apical third it varies from 150 to 200 μm. It is thicker in the distal surfaces as compared to the mesial surfaces and this can be explained by functional stimulation following mesial migration.
Hypercementosis or cemental hyperplasia is a prominent thickening of the cementum. It can be localized or generalized. It may appear as a generalized thickening of the cementum, with nodular enlargement at the apex or as spike like projections (cemental spikes). The etiology of hypercementosis is not very well understood. The spike like projections could be as a result of excessive tension from orthodontic appliance or occlusal forces. The generalized type may be associated with a variety of situations, like teeth without antagonists, in teeth with chronic pulpal and periapical infections. Hypercementosis of the entire dentition may be seen in patients with Paget’s disease.
==Also see==
===Cementoenamel Junction===
* [[Periodontal ligament]]
At the cementoenamel junction three types of relationships may exist. In about 60 to 65% of cases, the cementum overlaps the enamel, in about 30% of cases, end-to end relationship of enamel and cementum is seen and in 5 to 10%, the cementum and enamel fail to meet.
* [[Alveolar bone]]
===Cemental Resorption and Repair===
* [[Dentin]]
Cemental resorption may be caused by local, systemic or idiopathic factors. Local conditions that contribute to cemental resorption are trauma from occlusion, orthodontic tooth movement, pressure from erupting teeth, cysts and tumors, teeth without functional antagonist, periapical disease and periodontal disease. Systemic conditions that may predispose to cemental resorption are calcium deficiency, hypothyroidism and Paget’s disease.
* [[Enamel]]
* [[Periodontal disease]]
The resorptive process may not necessarily be a continuous process; it may alternate with periods of repair and deposition, which can be demarcated by formation of reversal line. Remodelling of cementum requires the presence of viable connective tissue and can occur even in non-vital teeth.
{{Tooth anatomy}}
[[Category:Dental anatomy]]
Cementum is not exposed to the oral environment because it is covered by alveolar bone and gingiva. In cases of gingival recession and as a consequence of loss of attachment in pocket formation, cementum can become exposed to the oral environment. Once exposed, organic substances, inorganic ions and bacteria penetrate the sufficiently permeable cementum. Caries of the cementum may also develop.
Basic anatomy of a tooth, showing the location of cementum.Diagram of a human tooth, illustrating the layers including cementum.Diagram of the periodontium, highlighting the role of cementum.
Cementum is a specialized calcified substance covering the root of a tooth. It is part of the periodontium, which also includes the gingiva, periodontal ligament, and alveolar bone. Cementum plays a crucial role in tooth support and stability by anchoring the periodontal ligament fibers to the tooth.
Cementum is a mineralized tissue similar to bone but is avascular, meaning it lacks blood vessels. It is composed primarily of hydroxyapatite, collagen fibers, and water. Cementum is classified into two types based on the presence of cells:
Acellular cementum: This type covers the cervical two-thirds of the root and is primarily responsible for anchoring the tooth in the socket. It does not contain cells within its structure.
Cellular cementum: Found mainly in the apical third of the root, this type contains cementocytes within lacunae. It is involved in the adaptive and reparative processes of the tooth.
Cementum formation begins during tooth development, after the formation of the root dentin. The process is initiated by the Hertwig's epithelial root sheath, which induces the differentiation of dental follicle cells into cementoblasts. These cementoblasts secrete the organic matrix of cementum, which subsequently mineralizes.
Cementum is essential for maintaining tooth stability and health. Loss or damage to cementum can lead to tooth mobility and periodontal disease. Conditions such as cemental tears and hypercementosis can affect the integrity of cementum and require clinical attention.
