A root canal crown and a post crown are both types of dental crown or cap that are fitted over a tooth that has had root canal treatment. From the outside, they look like any other crown or cap. You cannot tell by looking them that they are any different to a normal crown.
But underneath, they have very different foundations. There are subtle differences between the two types of crown.
A root canal crown can be fitted over a tooth that has had a root canal treatment, where the tooth is still strong enough to support a crown without any additional reinforcement. The hole over the root canal is sealed up, and the tooth trimmed down to the correct shape. The crown is like a thimble, and fits over the tooth. This reinforces the tooth, and provides an additional seal against bacteria getting into the root filling.
On the other hand, a post crown is fitted to a tooth that is NOT strong enough to support a crown on its own. Maybe there is very little tooth left above the gum. Not enough to support a crown.
In this case, a post crown is needed. Part of the root filling is removed, leaving a channel down inside the tooth. A post can be fitted into this channel, with the top sticking out of the top of the tooth root.
This post can be made of gold alloy, titanium, or of carbon fiber. Gold alloy posts are usually custom-made in a dental laboratory, whereas titanium and carbon fiber posts are prefabricated in various sizes and cut down to match the tooth being treated.
Carbon fiber posts can be manufactured to be very light in colour. This can be important if a front tooth is being treated. Metal posts can sometimes create a grey color to the gum edge. A light-colored post will not cause any discoloration. On the downside, they are not as strong as metal posts.
As always, there are exceptions to this rule! Here are some photos of a post crown with a bent post. I have only seen this once in 30 years of dentistry! The crown must have become a little dislodged, and when the patient bit down on something, bent the metal post. This is impossible to repair. A new post and crown was required.
For a back tooth, strength is the most important thing. The best post to use in a back tooth is a gold alloy post.
Once the broken-down tooth has had root canal treatment and been built up with a post, a crown can be put over it to restore it's shape and size. This is called a post crown, even though the crown is not actually joined directly to the post.
A root canal crown is simply a normal crown that is placed over a tooth that has had a root canal.