206 Theories and techniques of oral implantology

the age of forty. The mandible, particularly in the bicuspid and molar areas, is more often involved than the maxilla. The disease may be extensive, but it is self-limiting. The affected area may be enlarged, but pain is rare unless those lesions near the crest become inflamed or ulcerated—a common occurrence when conventional removable appliances are worn. After surgical removal of the lesions near the crest, a fixed implant-borne prosthesis may be possible if adequate bone can be found to support blade implants.

Eosinophilic granuloma. Eosinophilic granuloma is a form of histiocytosis X, a disease of unknown etiology involving the reticuloendothelial system. This particular form involves the bone, and for this reason is also known as histiocytosis localized in bone. The lesions are usually solitary and may occur in any bone other than those of the hands or feet. When they occur in the jaws, they may be the first and only signs of the disease. Multiple lesions in bone are rare, but when present they may be accompanied by soft tissue lesions.

Eosinophilic granuloma usually occurs between the ages of 20 and 40. It is more common in men than in women. When the jaws are involved, the patient may have a sore mouth, fetid breath, loose teeth, swollen gingiva with pus, pain, and swelling. Upon radiographic examination, the lesion or lesions are radiolucent and may be rounded, oval, or irregular in shape (Fig. 6-6) . They resemble islands of bone destruction in normal bone, although the bone immediately adjacent to the lesion may be slightly radiolucent. A lesion in the alveolar crest resembles a bone pocket caused by periodontal disease, making a tooth look like it is hanging in air.

Microscopic examination of an eosinophilic granulomatous lesion shows that histiocytes, or reticulum cells, and eosinophils have replaced bone marrow. The histiocytes are large cells and form al-most solid sheets that are interspersed with eosinophils.

The lesions may be excised or treated with radiation therapy. They usually respond favorably and in some cases regress spontaneously. Once bone repair has occurred and no recurrence of the condition is evident, implants may be inserted.

Follicular cysts. There are three types of follicular cysts: primordial, dentigerous, and multilocular. All arise from the enamel organ or follicle.

The primordial cyst is found where a tooth has never been present. The cyst apparently arises from a degenerated tooth germ. This particular type of

Fig. 6-7. Dentigerous cyst appears as a clearly demarcated radiolucent area. Tooth displacement is a common occurrence. (From Kolas, S., and others: Radiographic patterns of resorption seen in some gnathodental hard-tissue disturbances, Dent. Clin. N. Amer., November, 1968.)

cyst constitutes almost 2% of all odontogenic cysts and about 5% of all follicular cysts.

A dentigerous cyst develops in or from some part of an unerupted tooth follicle. As a result, the afflicted part undergoes cystic degeneration. The cyst may either completely surround the developing tooth or be attached to it (Fig. 6-7). The tooth usually involved is the mandibular third molar or the maxillary cuspid. Of all the follicular type cysts, the dentigerous cyst is the most common, comprising about 95% of them. About 34% of all odontogenic cysts are dentigerous. Because dentigerous cysts arise from developing teeth, they naturally appear early.

Another type of follicular cyst that is quite rare is the multilocular cyst. Although this type arises from the tooth germ and is always multiple, making the bone appear to contain soap bubbles, it does not involve the developing tooth. The condition appears to be a hereditary developmental disturbance, and multiple sebaceous cysts, multiple exostoses, and cervical vertebrae deformities are usually associated with it.

Follicular cysts require prompt attention and should be removed upon detection, since they may develop into ameloblastomas. About 30% of all ameloblastomas are known to arise from follicular cysts.