After getting a root canal, if the tooth has not much tooth structure remaining to support a follow-up dental crown work, the post-core may be needed. It is a little screw that goes into a root canal to support a crown. The post-core should be ideally going into a root canal 2/3 of the length leaving about 5mm of gutta-percha (root canal filling) remaining from the apex of the tooth. They must be tightly fit into the root canal even without cementation, otherwise, they may come loose over time. Posts come with different length and width, so your dentist would be selecting the most ideal size for the case by trial-and-error. Once the proper post is selected, it is cemented into the nerve canal and core-buildup material in the cavity. It is common practice to take x-ray prior to cementing the post to make sure the length is good. If the post is too short and not wide enough, the post has absolutely no function and it can cause a failure in the future. And if the post is going too deep, it can cause a root fracture or root perforation so the tooth may need to extract.
Types of post-core
⦁ Post core in chair-side – The post is properly selected from a choice of different size of stock posts and cemented into the root canal. It would be one visit case for most of the time. This is probably the most common practice in any dental office.
⦁ Cast Post-Core – Post coping is done on the first dental visit and sent to a dental lab for fabrication of a cast. Once the cast is ready, it is cemented into the root canal. This would take two visits. Sometimes, it is needed to go with this double step if the tooth has very little tooth structure remaining as this choice would be better in terms of strength, however, human errors can cause open margins, etc.
Once the Post-is cemented, core is built up and you are ready for a crown.
Please look at the link for crown if you want more info about a crown procedure: https://www.midentalclinic.com/what-is-crown