A crown is a cap that covers the tooth and may be needed due to: severe caries (decay), fracture, failed or failing existing restorations, to protect the tooth from fracture, after root canal therapy or for a combination of reasons. It generally takes two visits to complete the crown and a temporary crown is used while the permanent crown is being fabricated. A bridge is used to replace a missing tooth. It is a crown on each of the remaining teeth with a fake tooth in the space between.