Teeth develop from epithelial cells from the mucosal lining of the oral cavity and cranial neural crest-derived ectomesenchymal cells. These latter cells originate at the ectodermal/neuroectodermal junction of the developing brain, extending rostrally from the caudal boundary of the hindbrain and neural tube to the midbrain and caudal forebrain.
Teeth consist for the major part of dentin. This material houses the dental pulp, the soft tissue core of the tooth consisting of myxoid connective tissue with blood vessels and nerves, and supports the enamel cap that covers the part of the tooth that is exposed to the oral cavity. In the root area, dentin is covered by cementum that fixes the collagenous fibres of the periodontal ligament onto the root surface.
As enamel content is almost 100% mineral, it cannot withstand the decalcification needed to allow paraffin sectioning. Therefore, in general, it is not present anymore in the histologic sections and so, the histopathologist usually will not be faced with problems of how to interpret changes in this tissue type.
Tooth alterations occurring after eruption in the oral cavity are manifold. They may be due to a large variety of causes. Their effects may be gross form alterations or subtle changes only visible on histologic examination.
Pulpal diseases may be either inflammatory or degenerative. Very rarely, jaw tumours may grow through the apical foramen into the pulp space (Figs. 7.1a, b).
Disorders of the periodontal tissues can be divided into diseases of the marginal gingiva proper and those also involving the underlying bone of the alveolar socket. Gingival diseases may be either hyperplastic or inflammatory.
Cysts of the jaws are classified in several categories depending on histogenesis and etiology. Those that arise from odontogenic epithelium are called odontogenic; those that have their source in other epithelial structures are known as nonodontogenic [20]. The latter will not be discussed here.
Odontogenic tumours are comprised of a group of lesions which have in common the fact that they arise from the odontogenic tissue. They develop from the epithelial part of the tooth germ, the ectomesenchymal part, or from both. Their behaviour varies from frankly neoplastic, including metastatic potential, to nonneoplastic hamartomatous.
As already mentioned, immature odontogenic tissues may closely mimic odontogenic tumours. Quite often, it may be very difficult to decide if the structures visible in the slide are indicating the presence of an odontogenic tumour or if they are just remnants of tissues connected with tooth development. Two different parts of the immature tooth are important in this respect: the dental papilla and the dental follicle. Both will be discussed in some detail.
