IV. Cementum

A.  ORIGIN AND DEVELOPMENT

IV. Cementum

Cementum is the mineralized connective tissue resembling bone, that covers the roots of teeth and serves to anchor gingival and periodontal fibers. Some types of cementum may also form on the surface of the enamel of the crown.  Unlike bone, cementum is not vascular and exhibits little turnover. Cementum grows slowly, by surface apposition, throughout life.

The major function of cementum is the anchorage of teeth to the adjacent alveolar bone via the periodontal ligament.  However, it serves other functions as well.  Cementum is less susceptible to resorption than dentin.  Although it can be resorbed, it serves as a protective layer over the dentin.  Continuous deposition of cementum in the apical region compensates for rapid wear at the occlusal surface.

A. Developmental origin

In order to gain a better understanding of the structure of cementum, it is helpful to briefly review its developmental origin.  Cementum formation begins following the onset of root formation and elongation.   Root formation is guided by Hertwig's epithelial root sheath (HERS), a collar of epithelial cells derived from the apical prolongation of the enamel organ.  HERS is continuous apically with the epithelial diaphragm, the double-layered epithelium that separates the dental papilla from the surrounding dental follicle.

 Fig. 77:  Histologic section through developing root end.   Cells of the dental papilla (DP) in contact with the epithelial diaphragm (ED) differentiate (DO) to give rise to odontoblasts (O) responsible for the production of the dentin (D) layer.  The external shape of the root is determined by the position of Hertwig's epithelial root sheath (RS).  Coronal to the forming root end, ectomesenchymal cells from the dental follicle (DF) gradually displace the root sheath from the dentin surface and cause it to break up into the cell rests of Malassez (CR).

 

Fig. 78: Higher magnification of Fig. 77.  The inner cell layer of the epithelial diaphragm (ED) interacts with the adjacent cells of the dental papilla (DO) to induce the latter to differentiate into odontoblasts (O).  The odontoblasts proceed to form dentin (D).   Near the forming root end, the dentin is in contact with the epithelial collar of HERS (RS).  The dentin layer grows by apposition on the surface facing the dental papilla.  However, the shape of the root outline is determined by the position of HERS.                                 


Fig. 79:   Higher magnification of Fig. 77.  Ectomesenchymal cells (EMC) of the dental follicle surrounding HERS penetrate into the epithelium and lay down collagen fibers within the intercellular spaces of HERS and between HERS and the recently formed dentin (D).  In the process, HERS is displaced away from the dentin surface and is eventually fragmented into epithelial cell remnants, the epithelial cells rests of Malassez (CR).  The ectomesenchymal cells close to the dentin surface eventually differentiate into cementoblasts that participate in the formation of the cementum layer.





Fig. 80: Epithelial cell rests of Malassez (CR).  As Hertwig's epithelial root sheath is fragmented, it will form strands or islands of epithelial cells that remain close to the root surface.  The cell rests remain separated from the root by the non-mineralized collagenous tissue produced by the ectomesenchymal cells that originated in the dental follicle and contributed to its fragmentation.  The ectomesenchymal cells close to the root surface (EMC) will eventually give rise to cementoblasts that will produce cementum.  The process will be described in greater detail below.

 

 

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University of Pennsylvania and Temple University © 1999. All rights reserved. Created: May 8, 1999  Revised: URL: Max A. Listgarten: Comments to author: max@listgarten.com (Technical Support: Center for Dental Informatics: Heiko Spallek)