What is ferrule effect?

[manishapatel]

I am a newbie to preclinicals and sorry to bother you.. In our labs, the instructors keep talking about the "ferrule effect" It keeps goin over my head again and again..my frnds tried explaining it tom me but i couldnt get it fully cleared..what exactly is a ferrule and what is the ferrule effect with regards to tooth preps? how does it look, what is its purpose and how does one achieve it? are they required on every tooth or just any anterior or posterior only? what would happen if someone completely ignored this concept? these questions are killing me...can someone explain these things to me? any supportive links on the internet would be highly appreciated...
thanks a ton..

[UTDental]

A ferrule means "a metal ring or band around a slender shaft that prevents splitting". In dentistry it basically means a ring of solid tooth structure going around your crown prep. I believe most prosthodontists recommend 1 mm minimum of good tooth structure in order to put a crown on a tooth in order to have a decent prognosis (this doesn't include the build-up). I may be wrong about the 1 mm minimum- you definitely want as much tooth structure as possible going around the tooth. This creates what is referred to as a "ferrule effect" which improves retention and resistance. When you get in clinic, this will make a lot more sense. Do a search on Dentaltown of "ferrule" for more info.

[slayer]

The rotation of a post in the root canal, is known as Ferrule effect. To avoid this, an anti-rotation groove is placed in the coronal portion of the root canal.

[johnkimdmd]

This is something that's often confused. The ferrule is the ring of metal that goes along the gingival margin of a crown or a core buildup. It's not a ring of tooth structure. The tooth structure is removed in order to place a ferrule.

The theory is that a ferrule will help distribute lateral forces and prevent fracture after you do a post and core.

Think of a large amalgam buildup(*) placed over a post (P)

********
********
***PP***
***pp***
tttttPPttttt
tttttPPttttt
tttttPPttttt

If you prep this for a crown you want to remove a ring of tooth (t) structure so that you can have a ferrule encircling tooth structure and not amalgam.

CCCCCCCC
C**PP**C
C**pp**C
CtttPPtttC
tttttPPttttt
tttttPPttttt

Now you have some resistance against lateral forces that aren't translated only to post and core. c = CROWN


I hope this helps. Some may disagree. Whatever.

[simpledoc]

Originally Posted by johnkimdmd

This is something that's often confused. The ferrule is the ring of metal that goes along the gingival margin of a crown or a core buildup. It's not a ring of tooth structure. The tooth structure is removed in order to place a ferrule.

The theory is that a ferrule will help distribute lateral forces and prevent fracture after you do a post and core.

Think of a large amalgam buildup(*) placed over a post (P)

********
********
***PP***
***pp***
tttttPPttttt
tttttPPttttt
tttttPPttttt

If you prep this for a crown you want to remove a ring of tooth (t) structure so that you can have a ferrule encircling tooth structure and not amalgam.

CCCCCCCC
C**PP**C
C**pp**C
CtttPPtttC
tttttPPttttt
tttttPPttttt

Now you have some resistance against lateral forces that aren't translated only to post and core. c = CROWN


I hope this helps. Some may disagree. Whatever.

thats a very good reply john! vividly described and explained! going by your post, am just curious, so the width of the ferrule actually dpends upon the type of margin which we place on the crown prep right? So does that mean that if one were to place a knife edge margin or just a bevel margin, there will not be any ferrule effect and tthat would be detrimental to the crown...right?

[gumgardener2009]

Originally Posted by johnkimdmd

This is something that's often confused. The ferrule is the ring of metal that goes along the gingival margin of a crown or a core buildup. It's not a ring of tooth structure. The tooth structure is removed in order to place a ferrule.

The theory is that a ferrule will help distribute lateral forces and prevent fracture after you do a post and core.

Think of a large amalgam buildup(*) placed over a post (P)

********
********
***PP***
***pp***
tttttPPttttt
tttttPPttttt
tttttPPttttt

If you prep this for a crown you want to remove a ring of tooth (t) structure so that you can have a ferrule encircling tooth structure and not amalgam.

CCCCCCCC
C**PP**C
C**pp**C
CtttPPtttC
tttttPPttttt
tttttPPttttt

Now you have some resistance against lateral forces that aren't translated only to post and core. c = CROWN


I hope this helps. Some may disagree. Whatever.

I'll agree with you that this is often confused, but I'll disagree on your explanation. The ferrule effect is not between crown and tooth structure (your drawing make the ferrule effect look like the margin) but between tooth structure and post and core. You need a minimum of 2mm of tooth on which you make a 1mm circumferencial bevel upon which the core sits.

[oms fan]

JohnKimDMD is not incorrect in what he posted. In this scenario, the crown acts as the ferrule. However, what you are talking about is true as well...for example in a cast post and core you would prepare a ferrule for the casting to drop down around the tooth structure to resist fracture.
However, since you never want to leave the margin of a crown on anything but tooth structure, the crown will always be acting as a ferrule for a tooth that has a buildup.

[johnkimdmd]

I think my picture was a little confusing, and just showed one scenario. Yes, if you were doing the buildup over the core you would drop a margin around the tooth and build it up w/amalgam or whatever (I didn't draw that way). You could prep for crown either way so that the ferrule is produced from the crown or both core and crown. And as stated by osfan, definitely would seat crown on natural tooth.

J

[gumgardener2009]

It's good to know that we can both be right. I never thought about a crown always acting as a ferrule on a buildup. Sounds logical, but I'd like to look into that further. I know how prosthodontists can be sticklers for terminology. I'll probably ask one of them.

[Mr. So-So]

good stuff

Originally Posted by johnkimdmd

This is something that's often confused. The ferrule is the ring of metal that goes along the gingival margin of a crown or a core buildup. It's not a ring of tooth structure. The tooth structure is removed in order to place a ferrule.

The theory is that a ferrule will help distribute lateral forces and prevent fracture after you do a post and core.

Think of a large amalgam buildup(*) placed over a post (P)

********
********
***PP***
***pp***
tttttPPttttt
tttttPPttttt
tttttPPttttt

If you prep this for a crown you want to remove a ring of tooth (t) structure so that you can have a ferrule encircling tooth structure and not amalgam.

CCCCCCCC
C**PP**C
C**pp**C
CtttPPtttC
tttttPPttttt
tttttPPttttt

Now you have some resistance against lateral forces that aren't translated only to post and core. c = CROWN


I hope this helps. Some may disagree. Whatever.