Fig. 62: Transmission electron micrograph of the root surface at the onset of cementogenesis. Higher magnification of a region similar to that of Fig. 61. Bundles of extrinsic collagen fibers are arranged with their long axis perpendicular to the root surface which, at this stage of development, consists of dentin. The interdigitation of the collagen fibrils from the dentin and the cementum will form the future dentino-cemental junction.
Fig. 63: This is a diagrammatic illustration of the remodeling process in the dental follicle that leads to the formation of the mature periodontal ligament. The earliest remodeling takes place along the tooth (T) and the alveolar bone (AB) side of the dental follicle (Figs. A and B). Small bundles of collagen align themselves perpendicularly to the tooth and bone surface. they gradually grow thicker and longer, with the fibers on the bone side becoming wider than those on the tooth side. On the tooth side, the fiber bundles become incorporated into the developing cementum layer and on the bone side into new bone.
The imbedded portion of the fibers, known as Sharpey's fibers, become mineralized and part of these mineralized tissues. The Sharpey's fibers unravel at some distance from the mineralized surfaces to form an intertwined meshwork of collagen fibers with an orientation perpendicular to the mineralized surfaces (Figs. 63 C and D). Although one end of a fiber bundle may be in part non-mineralized and located in the ligament proper, while the other end is mineralized and imbedded in bone or cementum, only the part that is actually mineralized is be referred to as a Sharpey's fiber. Remodeling of fibers proceeds from the mineralized surfaces toward the central part of the ligament which is last to be remodeled. In the mature ligament, the Sharpey's fibers on the tooth side remain smaller and more numerous than on the bone side,
Incompletely remodeled ligament or sections through neurovascular
channels have been erroneously described in the dental literature as a so-called
"intermediate plexus", a zone believed to allow for mechanical
"slippage" between cemental and osseous fibers during rapid eruption. It
is recognized today that rapid tooth movement takes place because of continuous remodeling
of the structural elements of the ligament at the molecular level, and not by mechanical
accomodation of the fibrous elements.
University of Pennsylvania and Temple
University © 1999. All rights reserved.
Created: May 8, 1999 Revised:
Max A. Listgarten: Comments to author: email@example.com
(Technical Support: Center for Dental Informatics: Heiko Spallek)