kutlu erdogan - (5/15/2011 4:44 AM)

Thank you Stefano very much! I think exactly the same as you do and scientific researches confirm my clinical observations... What do you think about full-zirconia crowns and bridges such as "pretau, bruxzir and so on.." It seems they are gonna solve the chipping problem. Still, they have a long way to take to achive naturally esthetic outcomes. Do you think they might be the future if the esthetic problem is solved? Thanks..

James Hastings - (7/31/2010 5:52 PM)

Excellent presentation, well-reasoned, honest, and insightful. Thank you!

enrico manca - (7/31/2010 11:22 AM)

Thanks so much dott Gracis!

niki nikolov - (7/29/2010 10:18 PM)

Just in time!

Stefano Gracis - (5/16/2010 2:20 PM)

[quote=enrico manca]THANK YOU DOTT. GRACIS FOR THIS LESSON! BUT WHAT DO YOU THINK ABOUT FEATHER EDGE PREPARATION ( HERE IN ITALY IT IS BECOMING VERY VERY COMMONLY!!) AND ZIRCONIA OR METAL CERAMIC CROWN??
THANKS
ENRICO MANCA, CAGLIARI[/quote]


Dear Enrico, I know very well how feather edge preparations, in the recent months, have been under the spotlight in Italy because of the beautiful work shown by some well known clinicians who have demonstrated how this conservative preparation design can produce nevertheless a nice esthetic outcome thanks to the use of the zirconia. In the past, the feather-edge preparation margin design demanded the fabrication of metal-ceramic crowns with visible metal margins. Thus, they could not be easily employed in the anterior region. Nowadays, zirconia, with its high strength even in thin sections and its white hue, can be used on these preparations allowing the technician to have a very esthetic result all the way to the margin. It remains to be demonstrated that, in the long run (5 years or longer), these crowns will indeed perform satisfactorily under function and that leaving ample collars of zirconia exposed to the oral environment will indeed not cause any problem to the restoration.
Lastly, I am more apt at using a horizontal type of preparation (chamfer or shoulder) on anterior teeth NOT affected by the loss of periodontal support, in association with the fabrication of crowns in metal-ceramic, glass ceramics, alumina or zirconia depending on a number of variables. However, in selected situations I can certainly see the benefit of vertical preparations provided that they are carried out in the full respect of the surrounding periodontal tissues. Yours sincerely, Stefano Gracis

enrico manca - (5/3/2010 5:00 AM)

THANK YOU DOTT. GRACIS FOR THIS LESSON! BUT WHAT DO YOU THINK ABOUT FEATHER EDGE PREPARATION ( HERE IN ITALY IT IS BECOMING VERY VERY COMMONLY!!) AND ZIRCONIA OR METAL CERAMIC CROWN?? THANKS ENRICO MANCA, CAGLIARI

Stefano Gracis - (5/16/2010 1:59 PM)

[quote=sameh barsoum]beautiful presentation and excellent work with metal ceramics. Concerning the margin design as related to distortion following firing of porcelain: that's a problem we hardly see with base metal alloys. it does happen with precious alloys even when we follow the excellent margin triangle design by M. Kuwata [/quote]


Dear Sameh, thank you for your compliments and for posing the comment. I have to say that I have no problems in believing what you are saying, but I do not use base metal alloys. At least in my experience, I find that the ceramics developed so far for such alloys do not match in beauty the ones for precious alloys. Maybe, now that CAD CAM technology is allowing base metal alloys to be milled with a high degree of precision avoiding the pitfalls of casting, the ceramic manufacturers will be stimulated to develop better ceramics for these metals especially from the esthetic point of view. Yours sincerely, Stefano Gracis

sameh barsoum - (5/3/2010 4:22 AM)

beautiful presentation and excellent work with metal ceramics. Concerning the margin design as related to distortion following firing of porcelain: that's a problem we hardly see with base metal alloys. it does happen with precious alloys even when we follow the excellent margin triangle design by M. Kuwata

Stefano Gracis - (5/16/2010 1:54 PM)

[quote=julian jaramillo b]Dr Stefano, beautiful presentation, it would be very nice hearing your comments on best designs for zirconia frameworks, specially in long ones, and the ideal amount of zirconia exposed on non esthetic areas(effect of Newton´s law of cooling). Thank you very much.[/quote]

Dear Julian, thank you for your positive comment and for posing the question. The best design for a zirconia framework seems to be a design similar to the one made for metal-ceramics, that is a corrugated design that allows the veneering ceramic to be fairly uniform in thickness and well supported, especially in the areas where the stresses are highest (i.e., the palatal cusps of the upper posterior units). I have no data on the ideal amount of zirconia that can be left exposed. There is some controversy on this aspect since some authors believe that it can be subjected to "Low Temperature Degradation" and, eventually, break because of it. I am skeptical about it since I have used zirconia for implant abutments (which are typically left "naked") for a few years and, so far, I have not seen evidence of such a behavior.
In any event, I recently happened to read a well done short review of the technical problems associated with zirconia supported restorations done by 3M ESPE which I would suggest for you to obtain and read. It is part of the "Scientific Facts" of their "Espertise" booklet. It is titled: "Zirconia-supported ceramic restorations: uncovering the mysteries".
Yours sincerely, Stefano Gracis