Crowns (sometimes called caps) are used to restore badly decayed, broken, severely discolored, chipped, or misaligned teeth. The tooth is prepared by reducing it in size with a rotary instrument, removing about 1½ to 2 millimeters so the replacement crown will fit over it and have the same contours as the original. An impression or digital scan of the tooth with the surrounding teeth and also the opposing teeth is made, and will provide very accurate models. Using these models, the laboratory will fabricate the final crown. In the meantime, you will be given a temporary crown to wear. At the following appointment, the crown will be tried in, adjusted as needed, and then cemented into place.
While in the last 4 decades most crowns were made of a combination of metal frameworks with porcelain covering the surface, that has changed. Porcelain to metal units provide the excellent strength and fit of a metal coping with the esthetic appearance of porcelain. Newer all ceramic materials have changed the dental landscape. They have no metal framework and so no metal collar to show. Unlike the porcelain jacket crowns of years past, these new materials are quite strong and fracture resistant. Additionally, they are the most esthetic restorations we have ever been able to provide.
Interestingly, although the materials and methods have changed quite a bit in the last number of years, the preparation of a tooth for a crown has remained essentially the same. Crowns fit a tooth the same way 2 water glasses lock together when stacked. Nearly parallel walls give a friction grip and the cement or bonding seals the tooth, keeping the crown in place and the tooth strong.