How should post length be calculated according to the anatomical crown height?

The correct answer for calculating post length in relation to the anatomical crown height is that the post length should be equal to the height of the anatomic crown, but with 5 mm of apical gutta percha remaining. This principle is grounded in the balance between achieving adequate retention and support for the crown while ensuring that there is sufficient apical seal.

Leaving 5 mm of gutta percha apically is critical to maintaining a healthy periapical environment and ensuring that any potential leakage of bacteria or fluids is minimized. The 5 mm serves as a buffer to protect the apex of the tooth from infection and helps preserve the vitality of the surrounding bone. This technique recognizes the importance of both anchoring the post effectively to provide stability and allowing for protective measures that promote healing and health within the root canal system.

By aligning the post length with the height of the anatomical crown, it allows for a more natural distribution of forces during function, which is essential for the successful longevity of the restoration. In this case, the other options either suggest incorrect post lengths or compromise the apical seal, which would undermine the integrity of the endodontic treatment and the overall success of the prosthetic restoration.