[Pathomorphological study of maxillary invaginated incisor teeth].

Maxillary invaginated incisor teeth have been pathomorphologically investigated and some results have been obtained as follows: 1) The classification used in this study is as follows. That is, class I: Invagination is limited within the enamel. class II: Invagination extends toward the pulp chamber in a manner of pipe. class III: Invagination seen in class II expends at its end in the fashion of drop. class IV: Invagination occludes the whole coronal pulp chamber or extends toward the root apex beyond the cervical line. Frequent enamel-lined cavities of invaginated teeth were found to contain the contents (72.7%). Solid contents were found with considerable frequency in the cavities of the class I invaginated teeth of the author's classification (80.1%). On the other hand, the solid contents were rare in cavities of class III or IV (27.3%). In most cases, contents were found in limited areas of the cavity of class III or IV (72.7%). Any invagination corresponding to class II is not seen in this research. 2) The tissue composing the contents in the cavity of invaginated tooth was not clarified by the light microscopic observations of ground sections and film replicas. In class IV, poor hypomineralization was partly found in the inner enamel, and the dentin around the cavity was sclerotic. 3) As for the measurements of microhardess, the Vickers hardness number of contents in the cavities of invaginated teeth was approximately 1/4 of that of inner enamel. 4) The contents gave a higher radiolucency than the inner enamel by means of contact microradiography. 5) Electron microscopy revealed that the cavity contents of invaginated teeth was composed of poor inorganic elements resulting in a smooth aspect, and that, in most cases, a rod-having enamel was found in the surface layer of the contents and the rest of contents was composed of rodless enamel. An organic continuation of the tissue was observed between inner enamel and the contents. The results of electron microscopy, microhardness measurement, and contact microradiography, may indicate that the contents is composed of a hypomineralized enamel. 6) Caries incidence were found at a rate of 40.9% at cavity walls of invaginated teeth. Thus, it was suggested that cavity walls were susceptible of caries. In the contents of invaginated cavity, there was found primary caries appeared there.