Dentists will do absolutely everything in their power to try and keep your natural teeth in your mouth for as long as humanly possible, and medically permissible. This includes salvaging teeth until they are completely gone, and are frequently worn down to stubs, where only the tooth roots are healthy.
One of the most surprising kinds of dental restoration is the post and core, which is inserted into a tooth that is almost entirely gone and is used to stabilise the tooth and regain function even though the internal structures are entirely gone.
A post and core is a metallic little stick that is small enough to fit into your tooth, with a little metal ring at the bottom of it. This is inserted into the tooth, to stabilize it and to give the dental crown some balance and something to hold onto. The post and core stabilise the crown, and thus you do not need to remove the tooth for some more time.
If the tooth root is more or less intact, but the tooth is too far gone to be able to house a dental crown, then a post and core is inserted into the tooth to strengthen the tooth, and stabilise the dental crown. The teeth get in this condition from tooth decay usually, but a sudden traumatic event or a systematic problem can also leave teeth in a condition where they are just not strong enough to hold a dental crown up.
Getting a post and core is the same as getting a dental crown. People usually go in to get a dental crown because the tooth is broken or is so badly decayed that the internal structures of the tooth are visible already, and the tooth is open, and thus something needs to be done in order to stop pain or to be able to eat and chew. If the dentist notices that the tooth walls are simply unable to hold the crown in place, then they will tell you about it.
An impression needs to be taken, and in 5 business days, the post and core, and the dental crown that goes atop it are manufactured in the dental laboratory. You will have to come back and get the post and core fitted, and if it fits well and is not uncomfortable, then you are done.