A post and core crown is a type of dental restoration required where there is an inadequate amount of sound tooth tissue remaining to retain a conventional crown. A post is cemented into a prepared root canal, which retains a core restoration, which retains the final crown.
The role of the post is first to retain a core restoration and crown, and secondly to redistribute stresses down onto the root, thereby reducing the risk of coronal fracture. The post does not play any role in reinforcing or supporting the tooth and can, in fact, make it more likely to fracture at the root.
When deciding whether or not a tooth requires a post and core crown rather than a conventional crown you must establish the following:
1. Is there is a ferrule to retain a conventional crown?
2. Is the canal long enough to retain a post?
3. Are there large curvatures which would make post placement difficult?
4. Is the remaining dentine thick enough for post preparation?
5. Is a crown actually feasible in this tooth?
The benefit of placing a post into a root canal is improved retention of the crown. However there are also disadvantages, during the preparation for the post space there is a risk of perforation, a post can also make a tooth more likely to fracture, it makes future orthograde root canal treatment much more difficult and finally, it is very destructive and requires excessive removal of tooth tissue.
Posts are more commonly required for anterior teeth rather than posterior teeth. The primary reason for this is that multi-rooted teeth have a large pulp chamber which can be utilized for retention of the core and therefore the crown, whereas anterior teeth are much smaller and less retentive.
When it is not possible to retain a core on a posterior tooth and a post is required, no more than one post should be used per tooth, and this should be placed in the largest canal available. This is because more than one preparation for a post will involve excessive dentine removal and increase the fracture risk. A better alternative to posts on a posterior tooth is the use of a Nayyar core restoration which extends down into the entrance of the root canal.