All-Ceramic crowns, bridges and abutments are a class of dental restorations which are non-metallic. They can be made from pure porcelain (Most aesthetic crowns though lowest strength ), metal oxides (metal oxides look tooth colored or white and are VERY hard) or a combination of both. These restorations have gained considerable popularity from those concerned with metal allergies or reactions and in critical aesthetic situations. Generally, the advantage is that these materials allow light to shine through them like a natural tooth. Therefore they tend look more realistic than crowns which have a metal base (and usually look very solid and opaque).
Many of the commonly made crowns today are currently made from very high tech materials such as Lithium Disilicate and Aluminum/Zirconium Oxides which are tooth colored, extremely strong metal substitutes.
The current materials are very aesthetic, show good durability and are alternatives to metal containing restorations when necessary. Historically, they are not regarded as being as predictably strong as metallic restorations for patients who have very strong clenching habits or a history of chipping/breaking teeth however, several of the newest materials (Lithium Disilicate in particular)) show great promise with respect to durability. Use of metal oxides in bridges and implant abutments is possible but not without some caution with regard to predictability.