The implant site 55

Fig. 3-3. A Panorex showing distinct lamina dura.

Fig. 3-4. The trabeculae are the stress-distributors in bone architecture. Generally more trabeculae are evident in normal healthy bone. (From Sicher, H., editor: Orban's oral histology and embryology, ed. 6, St. Louis, 1966, The C. V. Mosby Co.)

around the various sinuses and cavities (Fig. 3-5). As might he expected, mandibular teeth, which are the aggressors during mastication, are surrounded by a great deal more supporting bone. The mandibular molars and premolars have especially thick and deep supporting bone. As the supporting bone in both jaws approaches the anterior teeth, it be-comes thinner buccolingually. The cortical plate is fused to the cribriform plate around the mandibular incisors and to the labial face of the maxillary incisors' cribriformn plate.

Periodontal ligament

Separating the tooth from its bony socket is a modified connective tissue—the periodontal ligament or membrane. This tissue is continuous with the connective tissues of the gingiva and completely surrounds the root of the tooth. In a healthy tooth in good occlusion, the periodontal ligament may range from 0.5 to 0.38 mm. thick, but its thickness varies in the same individual from tooth to tooth and in different areas of the same tooth. Normally the periodontal ligament is thinnest in the middle