Epithelial odontogenic tumours in domestic animals.

Epithelial odontogenic tumours are uncommon, poorly understood and often difficult to diagnose, oral neoplasms. Dental organ pre-ameloblasts and basal lamina induce development of mesenchymal cells into odontoblasts, which produce dentin and induce pre-ameloblasts to mature into secretory ameloblasts. These reciprocal sequential inductive interactions between dental epithelium and mesenchyme form the basis for classifying epithelial odontogenic tumours. There are three tumours classified as non-inductive: ameloblastoma characterized by cords and islands of stellate reticulum with peripheral palisades of polarized columnar cells, adenomatoid ameloblastoma which has acini, rosettes and ducts of polarized columnar cells and stellate reticulum and calcifying epithelial odontogenic tumour which contains foci of Congo-red-positive material surrounded by pleomorphic polygonal epithelial cells. There are five tumours in which induction of mesenchymal tissue is evident: ameloblastic fibroma with characteristics of ameloblastoma plus proliferation of closely associated pulp-like mesenchyme; dentinoma consisting of masses of dentin, often with minimal cellular component; ameloblastic odontoma which contains palisaded epithelium and stellate reticulum as in ameloblastoma, as well as foci of dentin and/or enamel; complex odontoma which is a disorderly array of dentin, enamel, ameloblastic epithelium and odontoblasts; and compound odontoma containing denticles with well-organized tooth morphology. This paper reviews the embryogenesis of teeth and describes six types of epithelial odontogenic tumours in 13 animals. The literature concerning these tumours in nearly 250 animals is reviewed. The most commonly reported tumour is ameloblastoma and the species in which all types are most commonly reported is the dog.