Zirconium
Where aesthetics come to the fore.
Zirconium Porcelain
Porcelains used in fixed prostheses are not resistant to forces alone. They are supported by metals or zirconium. No matter how much the metal is covered, it still has a reflection on the porcelain. Since the thickness of the porcelain used on the surfaces close to the gums will be thin, the gray reflection is more.