Ceramic has been used as a restorative material since the mid 20 s of the past century. Its physical properties (color, translucency, fluorescence) make this material the most suitable to replace missing teeth, while the mechanical features have pushed the scientific community to look for better and alternative solutions. The popularity of dental ceramics has dramatically increased in the 1960 s after the introduction of the metal-ceramic which made the material strong enough to withstand the occlusal forces even in the posterior area of the mouth. In the 1980 s the high esthetic demand has forced the industries to get rid of the undesired metal and concentrate their efforts on the development of full-ceramic metal free systems showing high fracture resistance. Many full-ceramic systems have been manufactured since and all in the same fashion: a very strong non-esthetic inner ceramic core reinforcing a layering highly esthetic but weak outer ceramic. The latter situation will configure a composite material which mechanically will behave differently than the two main materials and in the following text this behavior will be analyzed as far as fracture resistance.
Dan Nathanson, Fabio Scutella, Russell A. Giordano