Does everyone trim back their zirconia margins manually?

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Denture Dude

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.
 
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JMN

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Hey everyone. I'm a doctor in a big group practice with an internal lab, and I'm the liaison between the doctors and the lab. I was hoping you could help me out with this. Our lab mills zirconia crowns, the after they're sintered, they trim back the margins manually. Whenever there's a margin issue, my doctors say that the error is caused by the manual trimming, and that other labs don't do that. Our lab says that of course everyone does that - that's the only way it can be done. So who's right? Does everyone trim back their margins manually, and does that tend to be a big source of margin error?

You people are the best. You definitely answered my question, and I didn't even mind the sarcasm and rants :)
If you can put up with our acerbic humor, you come on back now y'hear?
 
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. That's where the real talent comes into play. Blending in the margin, maintaining at least 2 mm of blend of contour with emergence profile of underlying preparation. "Ring around the collar" (Tanaka) impressions give you that Really required anatomic reference to blend with.

can you link the article/publication you’re referring to with Tanaka and the ring around the collar?
 
Sda36

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can you link the article/publication you’re referring to with Tanaka and the ring around the collar?
Simply a term he uses for a succesful full margin capture impression. Also picks up anatomy of the tooth structure below the margin to assist in guiding emergence profile of the restoration to proper form. Good tissue management is essential to achieve this result.
 
JKraver

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About techniques used... not sure how the rest of you approach it but here’s what I do.
Follow pics.
First shows the White margin I see that needs finishing. I go at it with wheel spinning in reverse looking inside crown so I can see whats happening.
Second I do a light smoothing finish in reverse from buccal , wheel spinning away from margin.
Third shows buccal margin is finished.
that’s the way I skin this cat.
View attachment 38523 View attachment 38524 View attachment 38525
You use a homogenous rubber wheel in reverse? why? There is no direction in the cutting surface...
 
JKraver

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Direction of debris is away from eyes this way for how is being held
I am left handed, the debris is always away from eyes. Never considered this problem.
 
ps2thtec

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You use a homogenous rubber wheel in reverse? why? There is no direction in the cutting surface...
🤔…. did you see pics in post #20? I like to see the White edge margin as I’m finishing it back. For you being lefty, then run your handpiece in forward. Whatever works !
 
JKraver

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I bet that sucks to have to buy a mounted finishing wheel every time instead of mandrel based. I guess you could buy left handed mandrels.
 
sidesh0wb0b

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I bet that sucks to have to buy a mounted finishing wheel every time instead of mandrel based. I guess you could buy left handed mandrels.
i buy left handed mandrels. with the exception of carbides and diamonds i want that mess flying away from my face!
 
Davor RDT

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Hey everyone. I'm a doctor in a big group practice with an internal lab, and I'm the liaison between the doctors and the lab. I was hoping you could help me out with this. Our lab mills zirconia crowns, the after they're sintered, they trim back the margins manually. Whenever there's a margin issue, my doctors say that the error is caused by the manual trimming, and that other labs don't do that. Our lab says that of course everyone does that - that's the only way it can be done. So who's right? Does everyone trim back their margins manually, and does that tend to be a big source of margin error?
All margins have to be finished manually post sinter and I mean ALL of them from all machines and cam and cad softwares . So this was either over polishing or under finishing . Explorer picks it up from crown side it is over polished . Explorer picks it up from margin side it is under polished . No comment on model less crowns due to sheer lack of them where I work . As much as I know there is always offset at margin to be able to just mill it without chipping , now even if its thinned out to max there is still finishing needed after sinter .
The Techs are doing it properly but mistakes can happen . Impression? Modelwork? Crown too loose and when it moves one side is shy while other is overextended .
 
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Unless the shoulder allows for 0.5 mm zirconia, which seems to be the overall minimum for milling the material in the first place, we are getting an almost smooth explorer transition from prep to restoration. When that happens, I cry many happy tears and touch up manually (minimally) still. 95% of the time though we manually touch up all zirconia post-sintering margins; given that the impression was most accurate, our feedback from several offices have been that the margins are bang on.

It's one thing to say that the margins are off 'due to manual finishing' because there are a few factors to consider:
1. Is the prep appropriate for the material? If not 0.5 mm on the shoulder, with zirconia, there's no choice but to finish manually as the milling parameters can't go much below 0.5 mm.
2. Is the impression/scan accurate and if so, are the margins clearly distinguishable?
3. Who does the manual finishing? I've seen edges like the Grand Canyon and short margins as 'finished' ... and then there are ones who can get it to be sharp, smooth and accurate. And then, what technique is used in the lab? We use solid models with die separate die(s) so I have something to check my work on other than the one removable die that when damaged, isn't useful any longer. Try and invest in stable, hard and accurate die stone that does not crumble and/or chip away easily. (Sometimes we do work for other labs and that is my observation with the stone, reason for mentioning it). And, when printing, since the feedback has been positive, I reference (calibrate) the printed objects to the stone die once in a while. Trusting the printer to be bang on is another out of the box and/or every time is another thang.

It's all those little factors that can influence the outcome of a manually finished margin in my experience.
 

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