As a result of decay, the remaining tooth structure can become weakened and be at risk of fracture. By placing a crown over a tooth, all the biting stresses are transmitted to the root of the tooth, which is best able to absorb them.
Teeth which have been the subject of successful root canal therapy are particularly at risk of fracture. Not only has a substantial amount of tooth structure been lost, but also the tooth has a tendency to dry out and become brittle, and as such is no longer able to absorb the impacts associated with normal biting and chewing. Consequently cracks start to develop throughout the remaining tooth structure, which if left untreated, can lead to bits breaking off, or even worse.
Crowns can also used for cosmetic purposes to alter the shape and appearance of teeth. Nowadays, with the development of advanced ceramic materials, it can be impossible to distinguish a well constructed crown from a natural tooth.