are full coverage restorations that are used to encase a tooth that is likely to break or is too damaged to be restored with a filling. They are most commonly applied after a root canal treatment or when a large filling wears out. The larger the cavity hole, the more likely a crown will be needed. Even after a filling is put in a large cavity, a tooth is more sensitive to breaking. Teeth are subjected to tremendous pressures, and crowns ride over the weakened tooth, providing strength and protecting the tooth against breakage. A broken or cracked tooth is a far more serious matter and much more difficult to treat. Crowns prevent this, as well as restoring your nice smile. It takes two appointments to restore a tooth with a crown. In the first appointment, any decay is removed from the tooth and it is shaped to accept the crown. Then an impression is made of the tooth for use in fabricating a crown. Between the two visits the crown is made, usually of high-strength porcelain over noble metal, or all ceramic material. During this time a temporary crown is worn. In the second visit this temporary is removed, then the permanent crown is adjusted as needed before being cemented in place.