204 Theories and techniques of oral implantology

First affected are the bone marrow and soft tissues. At this stage the infection is hard to distinguish on x-rays; it may appear only as a thickening of the periodontal membrane shadow. As calcium begins to be removed from the bone, the trabeculae around the apex appear less sharp and the lamina dura shadow is thinner and less dense. As the infection spreads, the trabeculae appear thinner and less dense and eventually become discontinuous.

The growth of the infection is accompanied by pus production. As this accumulates the area swells and becomes warm and tender (Fig. 6-2) . Some-times the pus discharges itself by bursting through the now thinned bone. Frequently, however, it must be removed surgically by expiration or drains.

Until the infected site has completely drained and healed, no fixed restoration should be attempted. If the affected tooth is intended to be a natural tooth abutment, its stability is important to the success of the restoration.

Chronic apical infection. A chronic infection may also result from microbial invasion. Generally, the microorganisms that cause this type of infection are less virulent than those causing acute abscesses. They may arrive at the site through the root canal, by way of the periodontal membrane, or via the blood-stream.

Fig. 6-3. Histologic studies are needed to distinguish a dental granuloma from a radicular cyst or an apical abscess. The granuloma shown here resembles both other lesions. (From Bhaskar, S. N.: Synopsis of oral pathology, ed. 3, St. Louis, 1969, The C. V. Mosby Co.)

If the microorganisms reach the apex through the root canal, they are usually destroyed soon after their arrival by the natural defense mechanisms of a healthy body. If the patient is in poor condition, the microorganisms may survive and flourish to form a chronic dental abscess. In some cases, those micro-organisms in the apical tissues are destroyed, but others remaining within the root canal survive. These proliferate, and their toxins and metabolites reach the periapical tissues, where they provoke the development of a granuloma.

Granuloma. When chronic inflammation in or near the apex of the tooth causes the replacement of the periodontal membrane with granulation tissue, a granuloma forms. This is first manifested as a thickening of the periodontal membrane. As the granulation tissue accumulates, it pushes on the supporting bone. This resorbs and is replaced by even more granulation tissue, and the granuloma

Fig. 6-4. Sclerosing osteitis may A, occur as localized asymptomatic lesions or B, be accompanied by areas of rarefaction. (From Worth, H. M.: Principles and practice of oral radiographic interpretation. Copyright 1963 by Year Book Medical Publishers, Inc. Used by permission.)