I

The implant site 65

Fig. 3-21. The epithelial cuff is organically bound by a thin layer of cemental cuticle to a natural tooth. (From Sicher, H., editor: Orban's oral histology and embryology, ed. 6, St. Louis, 1966, The C. V. Mosby Co.)

tooth there is a layer of cementing substance, the dental cuticle, that binds the epithelial cuff to the enamel or cementum (Fig. 3-21). The firmness of this attachment is evidenced by extensions of the cuticle occupying spaces formerly serving as attachment sites for Sharpey's fibers.

Functional stimulation

Balanced occlusion is essential to the health of the periodontal tissues, and prolonged unbalanced occlusion gives rise to various disorders of the periodontium, masticatory musculature, and temporomandibular joint. Even when the teeth are in good occlusion, chewing tends to displace the maxillary teeth facially, the mandibular teeth lingually, and all the teeth mesially. These tendencies are counter-acted by movements of the tongue, cheeks, and lips. Thus the tooth is under continual pressure from several directions, either simultaneously or serially.

When a tooth in good occlusion meets its functional opponent, it is pushed down in the direction of the long axis of the tooth. The tooth is movable because it is not fused to bone but suspended in its socket by the principal fiber bundles of the perio-

dontal ligament. These fibers, which are crimped when the tooth is at rest, are extended by the occlusal force. Proprioceptive nerves in the periodontal ligament signal the masticatory muscles when the limits of normal extension are approached and protect the tooth from being overloaded. Sudden overload is indicated by pain receptors.

As the tooth is pushed, veins lying in glomuslike convolutions within the interstitial spaces of the connective tissue empty. This is protective, since the pressure created by compressing full vessels against the bone would cause its resorption. As soon as the tooth is released, blood quickly refills the con-volutions by way of arteriovenous anastomoses.

The Sharpey's fibers, which reach from the periodontal ligament into the alveolus, pull on the bone as the principal fiber bundles are extended by the occlusal thrust. This pull or tension, when within normal limits, encourages the formation of new bone.

Alveolar bone, like bone elsewhere in the body, is in a continual state of flux. In fact, of all the periodontal tissues it is the least stable. As long as there is mechanical stimulation, bone is continually being replaced be new bone. A coordination of both