Margin accuracy Milled Zirconia

[coffeebender]

I spend a lot of time, too much actually, doing fine adjustments to my zirconia crown margins. I'm trying to get them to be as good as my cast margins which are nuts -on. Is there anything I could be doing to improve them? I use Exocad, Medit T500, Top shelf crazy powerful computer, VHF K5+mill, Only fresh VHF burs, Talladium Dura Rock die stone and or fuji rock weighed and measured, all work done under a microscope. properly dried in a toaster oven, sintered in well calibrated Dekema with long slow progragram. Is this just as good as it gets? The fits I get on for example Straumann Ti bases are excellent. The impressions I get are also excellent but human preperations always have little variables that the software always seems to smooth over. I always try to buy the best equipment and materials available. Ultimately I get them to fit well but I would like it to be with less effort. Please help me, I cant be the only guy concerned about marginal integrity.

 

[coffeebender]

I spend a lot of time, too much actually, doing fine adjustments to my zirconia crown margins. I'm trying to get them to be as good as my cast margins which are nuts -on. Is there anything I could be doing to improve them? I use Exocad, Medit T500, Top shelf crazy powerful computer, VHF K5+mill, Only fresh VHF burs, Talladium Dura Rock die stone and or fuji rock weighed and measured, all work done under a microscope. properly dried in a toaster oven, sintered in well calibrated Dekema with long slow progragram. Is this just as good as it gets? The fits I get on for example Straumann Ti bases are excellent. The impressions I get are also excellent but human preperations always have little variables that the software always seems to smooth over. I always try to buy the best equipment and materials available. Ultimately I get them to fit well but I would like it to be with less effort. Please help me, I cant be the only guy concerned about marginal integrity.

Nobody has ever, ever complained about my margins this is all about what I see In the lab.

 

[Brett Hansen CDT]

I spend a lot of time, too much actually, doing fine adjustments to my zirconia crown margins. I'm trying to get them to be as good as my cast margins which are nuts -on. Is there anything I could be doing to improve them? I use Exocad, Medit T500, Top shelf crazy powerful computer, VHF K5+mill, Only fresh VHF burs, Talladium Dura Rock die stone and or fuji rock weighed and measured, all work done under a microscope. properly dried in a toaster oven, sintered in well calibrated Dekema with long slow progragram. Is this just as good as it gets? The fits I get on for example Straumann Ti bases are excellent. The impressions I get are also excellent but human preperations always have little variables that the software always seems to smooth over. I always try to buy the best equipment and materials available. Ultimately I get them to fit well but I would like it to be with less effort. Please help me, I cant be the only guy concerned about marginal integrity.

There will always be some finishing on the zirconia margins. There are milling parameters that must be met so the the margins don't chip that can cause a ledge that needs to be smoothed in. I also would look at how you are marking the margin on your preps in the design stage. I always mark "on top" of the margin as opposed to just over the side of the margin. 3shape has a function where you can see a zoomed in cross section of the margin while you are marking it to ensure you aren't over the edge of the margin. If you don't mark it on top, you get more of a ledge in the milled crown.

 

[Contraluz]

I cant be the only guy concerned about marginal integrity

You may...

I say this: ever since dentists started milling in-house, the worries about marginal integrity went down the drain...

It started with the first Cerec iteration by Siemens in the 80's. You could chase a herd of elephants through these margin gaps. Common phrase back then; the resin cement will fix it...

Things obviously got better and today we have quite a precise margin. But we gave up on al lot of values and achievements when we started using zirconia as our main restorative material. I am not complaining per se, since things got much simpler, too!

 

[Car 54]

3Shape D1000, VHF K5 very happy with the margins.

 

[RileyS]

I've come to agree with what contraluz said, there aren't a lot of high standards anymore. That being said, any new doctor that tries us out is always blown away with the margins we send back. We finish under 2x microscope and don't have any flaws with the margins. I have crappy and overused computers, a medit t500, a roland mill and vhf k4 classic. Not very well maintained. The roland has milled close to 5000 crowns on one set of milling tools, actually changed the 1mm once several months ago. It kills me that I have no idea what those burs are to buy another set !

 

[CoolHandLuke]

if you have a margin shaped like a pyramid you have to know no milling tool on earth can cut this margin.

this is exactly why sirona doesn't support dentists who prep how they want instead of by the sirona recommendation.

its why you shouldn't either.

 

[Rhuan BR]

I spend a lot of time, too much actually, doing fine adjustments to my zirconia crown margins. I'm trying to get them to be as good as my cast margins which are nuts -on. Is there anything I could be doing to improve them? I use Exocad, Medit T500, Top shelf crazy powerful computer, VHF K5+mill, Only fresh VHF burs, Talladium Dura Rock die stone and or fuji rock weighed and measured, all work done under a microscope. properly dried in a toaster oven, sintered in well calibrated Dekema with long slow progragram. Is this just as good as it gets? The fits I get on for example Straumann Ti bases are excellent. The impressions I get are also excellent but human preperations always have little variables that the software always seems to smooth over. I always try to buy the best equipment and materials available. Ultimately I get them to fit well but I would like it to be with less effort. Please help me, I cant be the only guy concerned about marginal integrity.

What the eyes don't see, the heart doesn't feel.

Jokes aside, we don't have a telescope to make this assessment.

I would check the useful life of the cutter, identification of the lines in the cam software and, as CoolHandLuke said, the shape of the edge.

 

[zero_zero]

Software tends to round up sharp features and at times the scanner cannot be fully trusted either. Here's what I did: wax block-outs specially around sharp j-preps and setup an extra pencil milling cycle with the 0.5mm tool between the two margin demarcation curves. Problem solved...

 

[desertfox384]

I dont know exo but in 3shape changing the margin offset would help with this - I finish under 10x and unless its a really sharp pyramid type margin line my margins are spot on.