The porcelain layer is attached to the metal and makes the crown look like a regular tooth. In comparison, the all-porcelain or all-ceramic crown does not have the layer of metal as part of the crown. The porcelain itself is what goes onto your tooth.
Quick Answer. An abyssal plain is a deep undersea area created by sediments overlaying a rocky crust, and they are the flattest places on Earth. Abyssal plains cover one-third of the Earth's surface, as much as all land above water, and they sit near continental borders and underwater mountain ranges.
The abyssal plain. The abyssal plains are the deepest regions of the ocean basins (with the exception of subduction trenches), and they form vast expanses of flat, cold, dark terrain. Here, the water can reach depths of over 5000 metres, so little or no light penetrates into the murky depths.