Idiopathic external resorption of teeth. 
An unerupted maxillary third molar tooth from a 57-year-old Caucasian male, which showed radiographic evidence of crown resorption, but was otherwise symptomless, was examined post-extraction by light and scanning electron microscopy. ( SEM) Appearances of the residual dental tissues were consistent with a diagnosis of an invading external resorption with formation of pulpal granulation tissue, dentinal resorption and some dentinal metaplasia.  SEM of crown fragments indicated a generally uniform pattern of enamel resorption, for which the ameloblasts rather than multinucleate cells were implicated.  By extrapolation of the activity of the former cells during the late stages of amelogenesis and tooth eruption, it is suggested that resorptive activity of and by enamel epithelium may explain not only the coronal origin of this type of idiopathic resorption, (which is otherwise unexplained), but also its progress into the pulp and the pulp reactions.