A crown is a tooth-shaped "cap" that is placed over a tooth - to cover the tooth to restore its shape and size, strength, and improve its appearance.
A crown/bridge works as a prosthetic device that is cemented directly onto existing teeth or dental implants.
Bridges are commonly used if you have one or more missing teeth. They are joint crowns and they cover the space where the teeth are missing. They are cemented to adjacent natural teeth or implants surrounding the empty space.
These are made using gold or "white" (silver-colored) dental alloy. They are almost obsolete due to their unaesthetic appearance.
A metal alloy is used to create a thin substructure that fits snugly over the tooth. Porcelain is then fused over the substructure to form the shape of the crown and give it a white tooth-like appearance.
They however have a disadvantage of showing a thin black line at the area where the crown meets the tooth and do not give a complete lifelike tooth appearance. They are thus not the preferred option, especially for anterior teeth. Also, in some cases allergies to the metal have been noted.
These crowns are fabricated using porcelain or "engineered" dental ceramic. These materials are known for their superior aesthetics and strength and are non allergic. They are the preferred option for anterior teeth.
Zirconia or zirconium is the hardest known ceramic in the industry and the strongest material used in dentistry. The zirconia used in dentistry is zirconium oxide, which has been stabilized with the addition of yttrium oxide.Zirconium is a very hard white ceramic that comes in the form of solid blocks of various shapes and sizes. For processing, it requires sophisticated computer systems (CAD/CAM systems). Because it is a white ceramic with very good translucency features, zirconium restorations are highly aesthetic and they do not contain any metal in their substructure.The zirconia core structure can be layered with aesthetic porcelain to create the final colour and shape of the tooth.