C. Principal fibers of the periodontal ligament
The periodontal fibers of the periodontal ligament are primarily composed of bundles of type I collagen fibrils. They have been classified into several groups on the basis of their anatomic location. The following constitute the principal fiber groups of the periodontal ligament:
1. Alveolar crest fibers
2. Horizontal fibers
3. Oblique fibers
4. Periapical fibers
5. Interradicular fibers
In addition to the collagen fibers, the periodontal ligament also contains oxytalan fibers that are related to the microfibrillar component of elastic fibers (see Fig. 31). They generally run parallel to the root surface, although they can occasionally insert into cementum.
Fig. 64 : This diagram shows the location of some of the principal fibers of the periodontal ligament. AC: alveolar crest fibers; H: horizontal fibers; OBL: oblique fibers; PA: periapical fibers; IR: Interradicular fibers.
The periodontal ligament is composed of collagen fibers that originate as fibers of different diameters at the mineralized surfaces where the fibers are continuous with their mineralized portion (Sharpey's fibers). These fibers are of a wider diameter on the bone side than the cementum side. Whether they originate from bone or cementum, they unravel into smaller fibers, which join up with those of adjacent fibers to produce a meshwork of interconnected fibers oriented between bone and cementum (Fig. 65). Thus, the periodontal fibers do not stretch cable-like from cementum to bone, but form a meshwork of interconnected fibers.
Fig. 65: Histological cross-section through a periodontal ligament on the distal surface of a single-rooted tooth. The periodontal ligament fibers (F) originate from relatively thin fibers (*) inserted into the cementum. After they unravel and become intermeshed with adjacent fibers, they form thicker fiber bundles that insert into bundle bone (BB), so named because it contains...