44 Theories and tecimplantologyhniques of oral

Stratified epithelium

Periodontal membrane

Cementum

Root canal

Sharpey's fibers

Fig. 2-24. A tooth is suspended in its bony socket by a dense periodontal membrane. As occlusion puts pressure on the tooth, the pressure moves the tooth and pulls on the Sharpey's fibers in the periodontal membrane. Because the fibers are connected to the bone, this pull creates tension on the bone. The resulting tension encourages osteogenesis, thus keeping the bone healthy. (Redrawn from Netter, F. H.: The CIBA collection of medical illustrations: the digestive system, vol. 3, part I, Surnmit, New Jersey, 1959, CIBA.)

Fig. 2-25. Well-occluded teeth provide just enough tension on bone to keep it healthy. In a patient with his full complement of well-occluded teeth and good oral hygiene habits, the bone is in excellent health.

normally to limit the extent of atrophy. Some re-sorption of the alveolar crest occurs, but resorption of the alveolar bone proper is rare.

In the area from which a tooth itself is lost, localized disuse atrophy also occurs. Here, however, the process is more complicated because new immature bone is formed to fill the empty socket. The normal healing processes continue up to a point. As the area is being reconstructed, mature bone is re-placing immature bone. The lamina dura is resorbed and replaced by spongy bone, the trabeculae of which are oriented according to the changed function.

As long as there are teeth with opposing teeth left in the neighborhood of the lost tooth, stress is being exerted in a horizontal direction and the trabeculae are aligned accordingly. The alveolar