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.
Wiktionary (0.00 / 0 votes) Rate this definition: abyssal plain (Noun). a large expanse of very flat and smooth ocean floor, usually found at depths of 4,600 to 5,500 meters (15,000 to 18,000 feet).