A possible explanation of what's happening at the moment of palatal shelf elevation

Cleft lip and palate is multifactorial in aetiology. The elevation of palatal shelves is a key point of palatogenesis. However, there were many different opinions on the explanation of the elevation. In this article, we offered a new explanation. Before sixth week of gestation in humans, Palatal mesenchymal proliferation was along the horizontal direction. Because of the block of the tongue, the palatal shelves had to grow first vertically in the oral cavity. In the process of cells migration, much horizontal stress accumulated in the palatal shelves, meanwhile increased the collagen secretion of the palatal mesenchymal cells in order to strengthen the elasticity of palatal shelf and maintain the integrity to make palatal shelf look like an elastic palate. The intrinsic elevating force and the block of tongue made the palatal shelf curved. After seventh week facial structures grew predominantly in the sagittal plane. The activity of the geniohyoid and genioglossus muscles caused the mandibular retraction and the widening of the angulation between the bilateral hemimandibles. These changes provided the space for palatal shelf elevation. At some moment of the eighth to tenth weeks, the elastic stress center of the palatal shelf was above the horizontal surface because of the drop of the tongue. The palatal shelves might bounce up and elevate in a horizontal position when enough horizontal stress accumulated, and then adhered and fused.