Cementum
Encyclopedia
Cementum is a specialized calcified substance covering the root of a tooth. Cementum is excreted by cells called cementoblasts within the root of the tooth and is thickest at the root apex. These cementoblasts develop from undifferentiated mesenchymal cells in the connective tissue of the dental follicle. Cementum is slightly softer than dentin and consists of about 45% to 50% inorganic material (hydroxylapatite
) by weight and 50% to 55% organic matter and water by weight. The organic portion is composed primarily of collagen
and protein polysaccharides. Sharpey's fibers are portions of the principal collagenous fibers of the periodontal ligament
embedded in the cementum and alveolar bone to attach the tooth to the alveolus. Cementum is avascular.
The cementum is light yellow and slightly lighter in color than dentin
. It has the highest fluoride content of all mineralized tissue. Cementum also is permeable to a variety of materials. It is formed continuously throughout life because a new layer of cementum is deposited to keep the attachment intact as the superficial layer of cementum ages. Two kinds of cementum are formed: acellular and cellular. The acellular layer of cementum is living tissue that does not incorporate cells into its structure and usually predominates on the coronal half of the root; cellular cementum occurs more frequently on the apical half. Cementum on the root ends surrounds the apical foramen and may extend slightly onto the inner wall of the pulp canal. Cementum thickness can increase on the root end to compensate for attritional wear of the occlusal/incisal surface and passive eruption of the tooth.
The cementodentinal junction is a relatively smooth area in the permanent tooth, and attachment of cementum to the dentin is firm but not understood completely. The cementum joins the enamel to form the cementoenamel junction, which is referred to as the cervical line. In about 10% of teeth, enamel and cementum do not meet, and this can result in a sensitive area. Abrasion, erosion, caries, scaling, and the procedures of finishing and polishing may result in denuding the dentin of its cementum covering, which can cause the dentin to be sensitive to several types of stimuli (e.g., heat, cold, sweet substances, sour substances). Cementum is capable of repairing itself to a limited degree and is not resorbed under normal conditions. Some root resorption
of the apical portion of the root may occur, however, if orthodontic pressures are excessive and movement is too fast. Some experts also agree on a third type of cementum, afibrillar cementum, which sometimes extends onto the enamel of the tooth.
The excessive build up of cementum on the roots of a tooth is a pathological condition known as hypercementosis
.
A 2010 archeological study has found that cementum has five times the amount of mitochondrial DNA
compared to dentine, which is commonly sampled.
Hydroxylapatite
Hydroxylapatite, also called hydroxyapatite , is a naturally occurring mineral form of calcium apatite with the formula Ca53, but is usually written Ca1062 to denote that the crystal unit cell comprises two entities. Hydroxylapatite is the hydroxyl endmember of the complex apatite group...
) by weight and 50% to 55% organic matter and water by weight. The organic portion is composed primarily of collagen
Collagen
Collagen is a group of naturally occurring proteins found in animals, especially in the flesh and connective tissues of mammals. It is the main component of connective tissue, and is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content...
and protein polysaccharides. Sharpey's fibers are portions of the principal collagenous fibers of the periodontal ligament
Periodontal ligament
The periodontal fiber or periodontal ligament, commonly abbreviated as the PDL, is a group of specialized connective tissue fibers that essentially attach a tooth to the alveolar bone within which it sits...
embedded in the cementum and alveolar bone to attach the tooth to the alveolus. Cementum is avascular.
The cementum is light yellow and slightly lighter in color than dentin
Dentin
Dentine is a calcified tissue of the body, and along with enamel, cementum, and pulp is one of the four major components of teeth. Usually, it is covered by enamel on the crown and cementum on the root and surrounds the entire pulp...
. It has the highest fluoride content of all mineralized tissue. Cementum also is permeable to a variety of materials. It is formed continuously throughout life because a new layer of cementum is deposited to keep the attachment intact as the superficial layer of cementum ages. Two kinds of cementum are formed: acellular and cellular. The acellular layer of cementum is living tissue that does not incorporate cells into its structure and usually predominates on the coronal half of the root; cellular cementum occurs more frequently on the apical half. Cementum on the root ends surrounds the apical foramen and may extend slightly onto the inner wall of the pulp canal. Cementum thickness can increase on the root end to compensate for attritional wear of the occlusal/incisal surface and passive eruption of the tooth.
The cementodentinal junction is a relatively smooth area in the permanent tooth, and attachment of cementum to the dentin is firm but not understood completely. The cementum joins the enamel to form the cementoenamel junction, which is referred to as the cervical line. In about 10% of teeth, enamel and cementum do not meet, and this can result in a sensitive area. Abrasion, erosion, caries, scaling, and the procedures of finishing and polishing may result in denuding the dentin of its cementum covering, which can cause the dentin to be sensitive to several types of stimuli (e.g., heat, cold, sweet substances, sour substances). Cementum is capable of repairing itself to a limited degree and is not resorbed under normal conditions. Some root resorption
Root resorption
In dentistry, root resorption is the breakdown or destruction, and subsequent loss, of the root structure of a tooth. This is caused by living body cells attacking part of the tooth. When the damage extends to the whole tooth, it is called tooth resorption...
of the apical portion of the root may occur, however, if orthodontic pressures are excessive and movement is too fast. Some experts also agree on a third type of cementum, afibrillar cementum, which sometimes extends onto the enamel of the tooth.
The excessive build up of cementum on the roots of a tooth is a pathological condition known as hypercementosis
Hypercementosis
Etiology of Hypercementosis can be caused by many things. A way to remember the causes is "PIG ON TAP" -PagetsIdiopathicGigantismOccusal TraumaNon functional toothTraumaAcromegliaPeriapical granuloma...
.
A 2010 archeological study has found that cementum has five times the amount of mitochondrial DNA
Mitochondrial DNA
Mitochondrial DNA is the DNA located in organelles called mitochondria, structures within eukaryotic cells that convert the chemical energy from food into a form that cells can use, adenosine triphosphate...
compared to dentine, which is commonly sampled.