Braces are also known professionally as crowns. In terms of current materials, all-porcelain dental crowns, also known as zirconium dioxide or aluminum dioxide, are the best. Because these crowns have no metal lining, they can be imaged without any artifacts. Crowns are divided into several grades, the lower grade is called ordinary metal porcelain teeth, there are nickel-chromium and cobalt-chromium porcelain teeth, these two porcelain teeth due to nickel-chromium will cause gum pigmentation, has been mostly eliminated, the clinical use of cobalt-chromium porcelain teeth. A grade up is called precious metal porcelain teeth, common is pure titanium porcelain teeth and gold and platinum porcelain teeth, these two porcelain teeth biocompatibility is better, but also widely used in clinical. The last type of porcelain teeth is called all-porcelain porcelain teeth, which is currently the best porcelain teeth.