III. Periodontal ligament
B. ORIGIN AND DEVELOPMENT
B. Origin and development
The periodontal ligament is derived embryologically from the ectomesenchymal tissue of
the dental follicle that surrounds the developing tooth in its bony crypt. At the
time of tooth eruption the cells and collagen fibers in the dental follicle, i.e. the
future periodontal ligament, are orientated primarily with their long axis parallel to the
root surface. remodeling of the follicle into a periodontal ligament begins at the
cemento-enamel junction and proceeds in an apical direction.
Fig. 58: Developing primary tooth in its crypt, at the time of eruption.
Although the crown of the tooth is fully formed, the root is still incomplete with a
wide-open foramen. The dental follicle around the developing root has been reduced
to a thin capsule of connective tissue that will be remodeled into the periodontal
ligament (PDL). Some of the pluripotential cells of the dental follicle that are capable
of producing bone, cementum and the ligament will be preserved as undifferentiated cells
in the mature periodontal ligament, usually in a perivascular location. remodeling
of the ligament begins at the cemento-enamel junction and proceeds apically. B, bone; CEJ,
cemento-enamel junction; ES, enamel space; M, oral mucosa; P, pulp;
PDL, immature periodontal ligament; TB, tooth bud of secondary dentition.
Fig.
59: Magnified view of Fig. 58, just apical to the cemento-enamel junction (CEJ).
Remodeling of the dental follicle into a periodontal ligament (PDL) begins near the
cemento-enamel junction following the formation of the dentogingival fibers (DGF).
Remodeling begins with the fibers that are closest to the root surface and the bone
(B). The process then proceeds in an apical direction until the entire follicle is
remodeled into a periodontal ligament, with fibers more or less perpendicular to the root
surface. B, alveolar bone; CEJ, cemento-enamel junction; DGF, dentogingival fibers; PDL,
periodontal ligament fibers.
Fig. 60: Magnified view of Fig.58, half-way down the root. The future periodontal
ligament space (PDL) is composed of connective tissue fibers orientated primarily parallel
to the tooth surface. Very little, if any, cementum can be detected at this time
over the dentin (D) which abuts the periodontal ligament space.
Fig. 61: Transmission electron micrograph of the root surface at the onset of
cementogenesis. Most cells, including fibroblasts (F), and fibers of the dental follicle
(DF) are orientated parallel to the root surface. Small collagen fiber bundles (EF)
adjacent to the root dentin (D) are becoming arranged perpendicularly to the root dentin
surface. These fibers are part of the
extrinsic fibers that will be incorporated into the cementum.
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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) |
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