236 Theories and techniques of oral implantology

giant cell tumors, osteoid-osteomas, and eosinophilic granulomas.

Osteomas usually occur as single or multiple exostoses, or outgrowths of bone. Oral exostoses are called oral tori. The condition is frequently hereditary.

Chondromas are usually found in the marrow cavity and can be considered central tumors. These must be carefully watched and treated, as they can undergo malignant changes.

Giant cell tumors involve the epiphyses of long bones, the pelvis, and the spine, as well as the jaws. They destroy the cancellous portion of the bone, expanding the cortical plate but usually not breaking through it. These tumors also tend to become malignant. Fortunately, they are rare in the jaws.

Fibrous dysplasia, also called fibrocystic disease, osteitis fibrosa localisata, focal osteitis fibrosa, and fibroosteodystrophy, is characterized by lesions composed of varying amounts of fibrous connective tissue and bone. The condition usually occurs in children and young adults but may also appear later in life. Females appear to be more afflicted than males, and at least one type of the condition appears to run in families.

The cause of fibrous dysplasia is unknown, but a growth disorder is suspected. The lesions usually grow slowly, with growth being continuous or intermittent. In most cases, once skeletal growth ends, so does that of the lesion. When the jaws are involved, the lesions are generally painless. The first clinical indication of the condition is swelling, and the dentist may be the first to note the lesions in routine dental radiographs. The maxillae are more often affected than the mandible, although, rarely, both jaws may be involved bilaterally, resulting in the facial appearance called "cherubism."

The molar and bicuspid regions are more typical sites for fibrous dysplasia than the incisor region, and the teeth tend to migrate. As the lesions expand, the cortex is pushed outward. It becomes thin but remains intact. Extensive maxillary lesions may re-place all or part of the sinuses; however, extensive continuous lesions resulting in gross deformities are rare.

In fibrous dysplasia the normal bone breaks down and is replaced by fibrous tissue and immature, disorderly arranged osteoid and cancellous bone. The ratio of these components varies widely in different lesions and in different parts of the same lesion. When bone predominates—usually around the up-per molar and bicuspid region—the bone appears to

be denser than normal with stippled areas that look like an orange rind (Fig. 6-44). When fibrous tissue predominates, there are large radiolucent areas. Typically in most cases there is a heterogenous distribution of fibrous and osseous elements (Fig. 6-45) .

There is no known cure for fibrous dysplasia. The disease is benign, although some doctors believe that sarcomatous changes may occur. When the lesions produce gross malformations (Fig. 6-46), these usually may be removed surgically. However, surgery is not recommended solely to prevent possible malignant changes. Because of the irregular structure of

Fig. 6-44. When bone predominates in a fibrous dysplasia lesion, the affected area has a stippled appearance, like that of an orange rind. This is the anterior region of the mandible; however, this type of manifestation is more common in the maxillae. (From Worth, H. M.: Principles and practice of oral radiographic interpretation. Copyright 1963 by Year Book Medical Publishers, Inc. Used by per-mission.)