A new culture method assuring the three-dimensional development of the mouse embryonic molar tooth in vitro.

Mandibular first molars from 17-day-old mouse embryos were cultivated in vitro for 10 days using a new organ culture method. This method consisted of using a small glass dish and an agar chamber to slowly float the molars to the gas-medium interface where they were maintained by the surface tension of the medium. The molars developed three-dimensionally through the use of this method. Five cusps with refractile dental matrix were recognized from the occlusal side. It was easy to determine antero-posterior and bucco-lingual orientation of the molars. Thick sections of the bucco-lingual plane showed the normal cytodifferentiation of ameloblasts and odontoblasts. The thick enamel layer was formed to the extent of the fissure region between cusps. Furthermore, a great quantity of stippled material accumulated between the enamel and the ameloblasts. The stippled material displayed a meshlike fibrilar structure, and at the mineralization front, it seemed that the fibrils of stippled material adjacent to the enamel had been transformed into needlelike enamel crystals. In addition, bundles of the fibrils similar to enamel crystals were found in the stippled material. As the floatation method resulted in the three-dimensional development of the molars and the development of the enamel without the presence of histological disturbances, it was considered superior to other culture methods for the facilitation of orientation and the development of cusps.