What thickness of "ferrule" is ideal for restoring teeth with significant structure loss?
Greetings Colleague-
The ideal tooth preparation is taper is 6 degrees. This results in the maximum ferrule effect to the tooth while allowing for cement outflow when seating a crown and appears very close to parallel to the unaided eye clinically. Interestingly, in conversation with a patient of mine who is a retired tool and die maker, he referred to a 5 degree taper as a "locking taper". Two materials milled to 5 degrees will fit tightly enough to lock. I know of one study that found the average tooth preparation convergence angle measured as 28 degrees.
Thanks Gary. Well ofcourse when we talk about the taper, it comes to about 4-6 degrees ideally. However; its the thickness of the ferrule itself, as in mesially or buccaly.
Thanks
Haroon-by thickness of ferrule do you mean height of the prep, i.e. axial height. If so, when a restoration is bonded rather than cemented 2.5mm of tooth structure (not including a build-up restorative material) is adequate for a predictable restoration. More height is necessary when cementing. The buccal and lingual height is more significant than interproximal to resist shear forces. If I'm restoring a tooth with short emergence past soft tissue, I'll use an all-ceramic bondable material like Emax and bond with a resin cement like RelyX Ultimate. I hope this is more the information you're looking for.
Regards,
Gary
Well, to be more precise, I was talking about the thickness. I have found something useful, please read thru and thank you very much.
Regards
http://www.nature.com/bdj/journal/v209/n1/pdf/sj.bdj.2010.580.pdf
You need a thickness of 2 mm to restore a teeth with significant tooth loss
Einer, ok and how much natural tooth would be sufficient ? One third, two third or complete ferrule is necessary ?
A minimum of 1 mm thickness of ferrule should be available. For the natural tooth structure it depends on the substance loss.