Before 1970, “fibrous dysplasia” was used as an all-inclusive term for both the monostotic and polyostotic forms of fibrous dysplasia described above and for a variety of other fibroosseous lesions, notably ossifying fibroma, cementifying fibroma, and osteoblastoma(Figure 7-14). Histologic studies often failed to establish definitive differences between these lesions, particularly in regard to the problems of the matura-
tion of the connective-tissue elements, the heterogeneity of large lesions, and inadequate biopsy specimens. The problem of separating these different lesions in the jaw bone is further compounded by the occurrence in the jaw of lesions with cemental as well as osseous differentiation (Figure 7-15) and the frequency of giant cell granulomas in this region. A number of papers that were published by oral pathologists during the late 1960s and early 1970s emphasized the variety of histologic appearances in fibro-osseous lesions that were derived from the periodontal membrane and distinguished them from similar lesions arising from medullary bone.The difficulty of differentiating tumors of periodontal membrane origin from tumors of medullary bone origin has long been recognized. Differentiation between the two is important because tumors of medullary bone origin usually behave in a more aggressive fashion even though they are essentially benign. The absolute proof of medullary bone origin in this group of tumors has not yet been shown, however. Benign fibro-osseous lesions of periodontal membrane origin are much more prevalent in the jaws than are fibro-osseous lesions of medullary bone origin. These latter lesions may be differentiated by clinical, radiographic, hematologic, and
histopathologic considerations. (For additional information on this topic, the reader should consult the reviews by Hamner, Wal dron, and Eversole.