Suppose your tooth is decayed to such an extent that more than half of your visible tooth structure is lost, then we may need to do a post & core treatment after the root canal to aid in reinforcing the tooth by covering it up with a cap.
A Post & Core is a dental restoration used to sufficiently build-up tooth structure for future restoration with a crown when there is not enough tooth structure to properly retain the crown, due to loss of tooth structure because of either decay or fracture. Post and cores are therefore referred to as Foundation Restorations.
The post itself is a reinforced carbon fibre or metallic structure that is placed within the root of a tooth that has had a root canal (endodontic procedure). When a root canal is performed, the pulp is removed and the space it occupied is filled with a special filling material. In placing a post, we remove some of this root canal filling material creating a space. The space that is created is used to anchor the post within the root of the tooth.
The type of post that is chosen will depend upon a number of factors. Most posts used nowadays are prefabricated. The appropriate size is selected depending on the tooth.
A core is built from filling material around the part of the post that sticks out of the root after the post is cemented into the root. The core is shaped so that it will anchor and retain a crown.
Although posts are usually recommended when there is minimal support for a crown, they are not always necessary. The use of a post is determined on an individual basis based upon the support and structural strength required.