POST AND CORE
Placing a Post and Core is a procedure that is required in order to rebuild and strengthen a tooth that has had root canal treatment. It adds the proper support necessary to restore a tooth with a cap or crown.
The post it self, is a metallic or reinforced fiber 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 nerve 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 today 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 support and structural strength required.
There is a variety of post and core systems. They are divided in different groups regarding to their functions, structures, method of production and name of the inventor.
According to the method of production, post and cores are divide into two main groups: prefabricated and cast. Both of these systems employ a metal post that is placed within the root canal or one of the root canals of the tooth being restored, and thus requires that the tooth be properly endodontically treated. After this procedure has been completed, and the root canal(s) is/are filled with the inert filling material in the root canal. This material is then removed from 3/4 of the canal extent. The space that exists on the upper part of the root , called the post space, is now available within which to place a post.
In cases when the need of a post and core is determined and a prior inadequate root filling is present, a retreatment must be done to try to obtain the best foundations possible before the upper access to the root is permanently sealed with the post. The dentist should always aim to have the best foundation possible to diminish the chances of further complications and tooth failure.
Prefabricated post and cores
Prefabricated post and cores take less time to place, as they do not involve any lab work and can be inserted immediately upon the decision to utilize them. They consist of two separate entities, each composed out of different materials, that are joined by the dentist at the time of the procedure. A universal metal post, sized for the particular diameter of the root canal, is placed as far down as possible into the post space and cemented with a permanent material.
After the prefabricated metal post is properly cemented into the post space, a core material can be packed around the cemented post. After the material has been cured or has had a chance to set and properly formed into a crown preparation, an impression can be taken for the fabrication of a prosthetic crown.
Cast post and cores
If added strength is required, a cast post and core can be custom fabricated for the tooth. A resin pattern is produced by placing a preformed plastic post into the space as though it were a prefabricated metal post and a resin material is used to build up the tooth to the proper dimensions. When this is completed, the pattern resin/plastic post is removed from the tooth structure and attached to a form. A single-unit cast post and core can thus be fabricated out of gold, or another metal using the lost-wax technique.
The use of a post and core does not strengthen the tooth prior to restoration with a crown. Rather, it may contribute to the weakening of the tooth structure, as the forces placed upon the future prosthetic crown and core are now transmitted along virtually the entire length of the brittle, endodontically treated tooth. This inherent drawback is taken into account when the prognosis of the finished restoration is determined and explained to the patient prior to the onset of treatment. It is because of this increased risk of failure, inherent in the use of post and core restorations, procedures requiring endodontic treatment, crown lengthening, post and core & prosthetic crown treatment, that the patient is sometimes advised to have the tooth extracted and an implant placed.
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