Crowns, also called “caps,” are a lab-fabricated type of restoration that fits over the entire tooth, similar to how to a winter hat pulls over your head. The tooth is shaped back and the crown then slides down over the tooth all the way down to the gum line and cemented in place with permanent dental cement.
Teeth that need crowns are typically teeth that are broken, have large cavities, cracks, or have previously had a root canal (which weakens the tooth). These teeth do not have enough healthy tooth structure to hold a filling. As a general rule, if the tooth has more than 50% of it covered with filling material, and the filling breaks or gets a cavity under it, your dentist will recommend a crown.
The first visit involves numbing the tooth and re-shaping it. Your dentist knows how much to shape and where, and will take an impression after the shaping is complete. The impression is sent to a dental lab where the crown is made. While the crown is being made (typically 1-2 weeks), you wear a temporary crown that is held in place with temporary cement. Some offices have a machine where the crown can be made the same day, but it varies from office to office.
Crowns are usually made of porcelain, gold or zirconia (zirconia and porcelain being the most popular today with porcelain-fused-to-metal being the least popular). Crowns on back teeth are almost always made from zirconia because it is incredibly strong, thin, conservative, and has no metal. Porcelain crowns are more esthetic, but not as strong, and are almost always used on front teeth. Your dentist will make the determination as to which type of crown would be best for you based on the location, your bite, etc.