Post-crown Preparations:
Understanding The Ferrule Effect (4)

Now, imagine a ring of metal encircling the coronal part of a root.

Can you see that if we drove a nail (called a post in dentistry!) into this root, the ferrule would help it resist fracturing ?

When the post is in position, and receiving lateral forces, the ferrule ensures the dentine is under compression (which it is good at).

If the was no ferrule, the dentine would be under tension (which it is poor at), and would fracture.

The ferrule effect comes not from the post or core, but from the crown ringing the dentine.

Ideally, the ferrule would go down as far as the post, but the periodontists might have something to say about that !