Cementogenesis

Posted by DAM on February 5, 2012 in Cementum | Short Link
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Cementogenesis

 

After the formation of the epithelial root sheath of Hertwig’s from the inner and outer dental epithelia of the dental organ, the root odontoblasts become differentiated and lay down dentin. Just prior to the fragmentation of the epithelial root sheath, A thin amorphous highly mineralized layer of cementum (about 10 um thick) is formed on the surface of dentin. This hyaline layer has been termed the intermediate cementum.


After deposition of the intermdiate cementum, the epithelial root sheath breaks down, and the adjacent mesenchymal cells of the dental follicle come in contact with the root surface, and differentiate into cementoblasts.

 

The sheath cells degenerate after they have completed their formative and odontoblast-stimulating functions. Remnants of epithelial root sheath may persist in the adjacent connective tissue of the periodontal ligament as strands or clusters network designated as the Epithelial rest of Malassez.

Cementogenesis proceeds at a slower rate than that of the adjacent root dentin.

 

The newly formed cementoblasts elaborate organic matrix which consists of collagen fibers (intrinsic) and ground substance.

Adjacent fibroblasts elaborate collagen fibers (extrinsic) which become embedded in the cementum matrix to provide attachment of the tooth to the surrounding bone. The embedded portions of the periodontal ligament fibers in the cementum are known as Sharpey’s fibers.

The fibers of the first formed cementum matrix may be entirely extrinsic fibers and are oriented perpendicularly to the root surface. Additional collagen fibers which run mostly parallel to the root surface and weave a lattice around the extrinsic fibers are contributed by the cementoblasts together with the ground substance.

In the following layers of cementum. organic matrix is fonned from roughly equal proportions of extrinsic and intrinsic collagen fibers.

Mineralization begins after some cementum matrix is formed. Calcium and phosphate ions present in tissue fluids are deposited into the matrix and are arranged as crystals of hydroxy apatite along the fibrils. Apatite crystals can be seen clustered into groups of nucleation centers as found in bone calcification.

The first formed cementum is acellular and develops relatively slowly as the tooth is erupting and covers at least the coronal two thirds of the root.

After the tooth is in occlusion, more rapidly formed and less mineralized cementum is deposited around the apical two thirds of the root. The cementoblasts usually become trapped within the developing cementum where they occupy lacunae and become cementocytes or they may remain on the surface of the newly formed cementoid tissue.

 

Function:

  • The primary function is to furnish a medium for the attachment of collagen fibers that bind the tooth to the alveolar bone.
  • It serves as the major reparative tissue for root surface.
    • It helps functional adaptation of the tooth. Deposition of cementum apically can compensate for the loss of tooth substance resulting from occlusal wear. Continuous growth of cementum is essential for the continuous eruptive movements of the functioning teeth.

 

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