Post-crown Preparations:
Understanding The Ferrule Effect (5)

Here's a representation of the preparation:

1	Dentine prepared to receive ferrule
2	Space prepared for post
3	Post and core fitted
4	Crown provides the ferrule effect. Lateral forces transmitted from the crown to the post result in dentine compression coronally.

The yellow area is the part of the crown that provides a ferrule (Radiograph No 4)

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	This post-crown prep has a 2mm ferruled area all the way round. The ferrule preparation should incorporate at least 1 to 2 mm of dentine all round the tooth.         Click these images to see the preparation shapes
	This post-crown prep only has a partial ferruled area. This tooth has a limited life ahead of it. Expect post decementation, or root fracture. Once the crown is on, lateral forces will put the dentine and the post-cement under tension. One or the other will give !

If you can not achieve a ferrule effect (as in the picture above), you should consider crown-lengthening (to expose more dentine), an overdenture, or extraction.

What are the options for crown-lengthening?