A cellular mechanism for the palatal shelf reorientation from a vertical to a horizontal plane in hamster: light and electron microscopic study.

Cellular and subcellular events during reorientation of the palatal shelf in hamster fetuses are described. An alteration in the morphology of the epithelial and the mesenchymal cells is observed during shelf realignment from a vertical to a horizontal plane. The mesenchymal cells elongate and subsequently appear to protrude in the medially bulging palatal shelf. Microtubules, microfilaments and close contacts are associated with elongation of the mesenchymal cells. The cells of the thickened epithelium may play a mechanical role in providing direction to the mesenchymal cells during palatal shelf reorientation. The altered morphology of the mesenchymal cells may be associated with the intrinsic shelf force implicit in Walker and Fraser's theory of palatal shelf reorientation.