Ameloblastoma with dentinoid induction: dentinoameloblastoma.

Ameloblastomas do not generally show evidence of induction, however rare cases associated with an odontome have been reported, and are referred to as odontoameloblastoma. In this paper the first known case of an ameloblastoma showing evidence of induction of dentinoid by tumor cells but without concomitant formation of enamel is recorded. The lesion occurred in the angle and ramus of the mandible of a 24-yr-old Asian man and was largely unicystic. In one area however, solid tumor was present which consisted both of infiltrating follicles of typical ameloblastoma tissue and solid sheets of ovoid to spindle cells containing abundant amounts of a homogenous eosinophilic extracellular material, interpreted as dentinoid, and psammamomatous type dystrophic calcifications. Electron microscopic examination of formalin-fixed tissue showed this dentinoid material to consist of interlacing collagen fibrils embedded in a structureless ground substance. At the periphery of the dentinoid globules the collagen fibres were arranged in parallel layers. A final diagnosis of dentinoameloblastoma was made.