抄録
Stages of the development of the junctional epithelium (JE) during molar tooth eruption in Wistar rats were studied at the ultrastructural level and following results were obtained.
1) At the time of first emergence of the cusp tip into the oral cavity, prominent bud-like proliferation of the external cells occurs throughout the lateral side of the reduced enamel epithelium (REE). With progress of tooth eruption, these newly formed epithelial cells provided with well-developed Golgi complex and lysosome-like bodies successively replace the preexisting REE cells and are transformed into flattened cells arranged parallel to the enamel surface presumably by means of the cytoplasmic reorganization with autophagosomes. It is evident that the JE immediately after completion of the eruption totally consists of the odontogenic epithelial cells derived from the REE.
2) With exposure of the cusp tip into the oral cavity, intracytoplasmic vacuoles begin to appear within the external cells already transformed into squamous cells. Leukocytic emigration into the epithelium also starts with tooth exposure. These vacuoles rapidly increase their number and extent as the tooth eruption proceeds and finally exhibit the similar morphology and distribution pattern to those characteristic of the mature JE. These findings strongly suggest that they are phagocytic vacuoles and play an important role for defense mechanism in highly permeable JE.
3) Separation between the tooth crown and the gingiva during eruption does not occur at the dento-e pithelial junction but is constantly observed as a tear within the REE or JE. A layer of non-vacuolated epithelial cells always persist adhered to the tooth surface facing the crevicular space. It seems, therefore, that the gingival sulcus in rat molar gingiva develops by degeneration and shedding of the cells constituting a superficial (coronal) portion of the JE.
