A developmental malformation of the teeth in which there is an invagination of the enamel giving the radiographic appearance of a ‘tooth within a tooth’. It can be caused by the prolific growth of the ameloblast and odontoblast cell layers during tooth formation. It most commonly occurs on the palatal surface of permanent maxillary lateral incisors and presents as a blind channel opening on the cingulum pit which is susceptible to caries. They may be described according to the extent of the invagination (Oehlers' classification, as described by F. A. Oehlers in 1957): type 1 is an enamel-lined invagination occurring within the confines of the crown of the tooth, not extending beyond the cemento-enamel junction; type 2 is an enamel-lined blind sac which invades the root and which may or may not connect with the dental pulp; type 3 is an invagination which penetrates through the root, perforating the apical area and forming a second foramen but with no immediate connection with the pulp. See also odontoma.
Vaidyanathan M., Whatling R., Fearne J. M. An overview of the dens invaginatus with case examples. Dent Update 2008;35:655–63.