Scanning electron microscope study of the medio palatal epithelium: Simultaneous modifications characterizing fusion and degenerescence processes.

The surfaces of the palatine shelves undergo important modifications at the expected zones of fusion immediately preceeding contact. Epithelial degeneration occurs just before and during midline contact and adhesion. The cells retract, become less closely associated with their neighbours and finally their boundaries disapear. Their surface become wrinkled whilst at the same time, blebs and short irregular filaments are observed. These features are interpreted as being morphological characteristics of tissue degeneration. This loss of cohesion may favour the spreading and convergence of the expected zones of fusion towards the midline, and then towards the anterior and posterior extremities. On the contrary, during the process of joining certain portions of the surface swell and converge at the expected zone of fusion. In these regions, the area of contact increases firstly in a naso oral direction. Successive layers are made on which large expansions spread (making) to form bridges between the walls.