Many a times in our practice we come across cases where it becomes hard to react, imagine a patient comes to your office with a post core and the crown in his hand.. What would you do?? make a new more retentive post or do you use a cement which would have a greater tensile strength??Most of the time we fail to check for a proper "ferrule".
A ferrule effect is defined as the envelopment of the tooth structure by a crown.
According to studies it is shown that 1.5mm of tooth structure is sufficient enough to ensure the transmission of masticatory forces to both the post and tooth. A tooth broken at the gum line offers no form of resistance to transversal forces and thus the post has to take the entire load, in this there is a high chance for the cementation to fail.
When the tooth fractures at the gum line it is important to gain a 1.5mm ferrule by bringing the marginal finishing line of the future restoration more apically. In theory, the marginal finishing line of the crown should be no less than 2 mm from the bony ridge, as there is a risk that it could
lead to an inflammatory response that is commonly known as violation of biological width.
(Biological width is a 1 mm attachment of connective tissue; a 1 mm attachment of epithelial tissue; and a 0.7 mm sulcus depth.)
To obtain an adequate ferrule effect for teeth that are fractured at the gingival level the following can be done
- Gingivectomy
- Osteoectomy
- Orthodontic extrusion
Dentine prepared to receive ferrule
Post and core done
Crown here provides the ferrule effect. The lateral forces transmitted from the crown to the post cause compression of dentin coronally.
2 comments:
By far the best explanation I have read of the ferrule effect. Thank you!
Congratulations!
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