What should the size of a post and core be in relation to the canal?

The size of a post and core should be undersized in relation to the canal for several important reasons. An undersized post allows for adequate retention and support within the root canal while preventing excessive stress on the remaining tooth structure. This is crucial because an overly large post can lead to fracture of the tooth or weaken the surrounding dentin, making it more susceptible to failure.

Moreover, maintaining a space within the canal helps accommodate for the variations in canal anatomy and allows for some degree of flexibility. This can be particularly important when considering the possible movements and forces that can occur in the oral cavity once the restoration is in place. An undersized post can also provide sufficient space for sealers or other materials intended to fill the canal, ensuring that there is no compromise in the sealing properties which are vital for preventing bacterial invasion and potential re-infection.

In contrast, if a post were to be equal to or oversized in relation to the canal, it could compromise the integrity of the tooth structure and lead to complications such as root fractures or difficulties during the placement, thus impacting the overall success of the prosthetic restoration.