With the exception of odontomas, odontogenic tumors are quite rare, probably constituting fewer than 1% of all jaw cysts and tumors.Some, such as the ameloblastoma and the calcifying epithelial odontogenic (Pindborg) tumor, are undoubtedly neoplastic; others, such as the compound odontoma and periapical cemental dysplasia, are most likely hamartomas. Malignant variants of several odontogenic tumors also attest to the neoplastic nature of at least some odontogenic growths.Although there have been many attempts at classifying odontogenic tumors, uncertainty concerning the cells of origin of many of these lesions, the bewildering array of histologic types of odontogenic tumors that result from inductive changes in the mesodermal component of these lesions, and their relative rarity all cause difficulty in the histopathologic diagnosis of some of these lesions.
For the majority of these lesions, the descriptions and illustrations included in the 1971 WHO classification of neoplasms and other tumors related to the odontogenic apparatus remain unchanged although the categories of squa-TABLE 7-2 Histopathologic Classification of Odontogenic Tumors
For the majority of these lesions, the descriptions and illustrations included in the 1971 WHO classification of neoplasms and other tumors related to the odontogenic apparatus remain unchanged although the categories of squa-TABLE 7-2 Histopathologic Classification of Odontogenic Tumors
mous odontogenic tumor and clear cell odontogenic carcinoma are generally included in more recent classifications. Subclassifications of epithelial, mesenchymal, and mixed epithelial and mesenchymal origin (Table 7-2) and subclassification of noninductive versus inductive have also become common practice.
Of most significance to the clinician is the basis for the typing and classification of odontogenic tumors because the various designations are cause for bewilderment. These tumors are classified according to their emulation of the process of odontogenesis, their differentiation, and the tissues from which they are derived. Recall that the epithelial portion of the tooth germ arises as an invagination of the primative oral ectoderm into a linear strand of cells, the dental lamina. The tip of the lamina undergoes bulbous expansion to form the cap and bell stages of odontogenesis, with differentiation into the ameloblastic layer and the inner zone of stellate reticulum. During the differentiation of the odontogenic epithelium, the underlying connective tissues condense with cells recruited from the neural crest. This ectomesoderm transforms into the pulp, and those cells that lie in juxtaposition to the epithelium differentiate into odontoblasts. Once the crown morphology is outlined, dentinogenesis proceeds initially and is a requisite for subsequent amelogenesis. The cervical epithelial tissues then invaginate once again to outline the morphology of the roots as Hertwig’s sheath. Surrounding periodontal connective tissues then form bone on the alveolus side of the process and form cementum on the tooth side.
These developmental stages are emulated in various odontogenic tumors. Those that derive strictly from epithelium do not show dentin formation since no ectomesoderm is a component of the neoplasm. Indeed, no enamel formation can be seen because dentin (the prerequisite for amelogenesis) is lacking. Conversely, the mixed odontogenic tumors.