They are crowns but unlike the classical crown, they do not contain metal, so the light can go through the crown and with time you cannot see a metallic border near the gum.
They are made of different materials, zirconium core coated with ceramic or entire porcelain.
The teeth have to be prepared and temporary crowns are needed while the permanent ones are being made.
metallic structure for classic crowns
Zirconium structure
