58 Theories and techniques of oral implantology

tooth, the periodontal ligament also contains blood vessels, lymphatics, and nerves. These occur in spaces between the principal fiber bundles, surrounded by loose connective tissue containing various immature or undifferentiated cells that participate in the resorption and formation of bone and cementum.

The main blood supply arrives via vessels branching from the interalveolar arteries and passing through the alveolar bone proper (Fig. 3-8). Other vessels also arise periapically from blood vessels to the pulp, and the gingival arteries anastomose with those of the periodontal tissues. The arteries branch into numerous capillaries within the periodontal ligament. These are connected to veins that form glomus-like convolutions in the interstitial spaces (Fig. 3-9) .

Following the blood vessels are lymphatic vessels, which flow toward the alveolar bone, and nerves. The nerves, which arise principally from the interdental nerves in the interdental septum, form a rich plexus in the periodontal ligament. The ends of some form knob-like swellings, others loop around the fiber bundles, and still others are free. These latter are pain receptors, Most of the others ate receptors for proprioceptive stimuli and allow ac-curate localization of degree and direction of pressure. They protect the tooth by regulating muscle activity during mastication.

Also found in the periodontal ligament close to the cementum are nests of epithelial cells, the epithelial cells of Malassez. These are remnants of the epithelial root sheath and may proliferate and give rise to pathologic conditions associated with granu-

Epithelial rest

Cementum

Fig. 3-9. Within the periodontal ligament arc islands of loose connective tissue containing blood vessels and nerves. The invagination of one of these islands with its glomerulus of blood vessels marks an area of bone particularly sensitive to pressure. (From Sicher, H., editor: Orban's oral histology and embryology, ed. 6, St. Louis, 1966, The C. V. Mosby Co.)