Weird crown bottom, Exocad, IOS

PCdental

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Good day all!

I have an IOS I am trying to design, and after I mark the margin, the crown bottom produced is wacky. Does anyone know why this is happening or how I can fix it?

Thank you!
 

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2thm8kr

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In expert mode, right click in an open area of the background. Look for adjust scan data orientation.
ASDO.png

Check and see if the mesh is inverted.
 
DAL Claxton

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Good morning @ PCdental! I want to check first if you are using a material configuration other than the default? Some companies when creating theirs are too used to the wording 3Shape uses. Namely the "additional spacing" verbage. You should leave the additional spacing as .02. The reason this is there is to allow for passive seating. Otherwise, the 0 cement gap green zone would make the crown impossible to seat.

Any changes you make to gap should be done by changing the yellow gap zone, or adding in an additional light blue zone. The green 0 CG zone should only really be where you want the marginal seal.

That prep is a little odd to start with on the lingual margin, but the huge gap between your prep starting cap and your actual prep is there because of that additional spacing.

I'm attaching an example screenshot for you. In it, you can see there is the offset of the .02 where the green 0 CG is. If you increase this gap, then the blocking out set by the undercuts tab tends to get a bit... wonky.

*** EDIT : in the undercuts tab, also turn on that protected zone near margin. Otherwise if the Dr. has an undercut to the margin, then you will have a wide open margin because it will block it out all the way down. The protected zone will close the margin the amount you have it set to.

I hope this helps!
- Josh
Additional Spacing Example.png
 
PCdental

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Thank you so very much! :) Is the undercut setting correct?

Do you use the same additional spacing settings on all of your crowns? I haven't had this issue with scanned models or other intraoral scans.
 

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DAL Claxton

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That looks a lot better haha. Yes, the additional spacing is always the same. We never even open up that drop-down. The reason my CG is as low as it is in my SS is because this was an over-implant that needed a little better retention. Depending on your mill/printer your could need yours higher or lower. If you're used to additional spacing that high, then it's likely this fit might be too tight for your liking, though that is a shallow prep so a little tighter could work in your favor.

I believe the only reason that it hasn't presented itself is because this prep is kind of.. unique looking on the lingual, so it's more likely to show errors. Kind of like dominoes, the more problems there are to start with, the worse it looks down the line. If preps look ideal then other problems appear to be less of an issue.

You're going to want to make a couple of quick prints/mills out of extra material if you have it available to check which settings will work better for you though. On a prep with any length of axial wall, try .05 as a good base (exocad default is .08 which I think is a little loose) and tweak everything in from there.

Good rule of thumb for ideal fits :
* Green "0" cement gap zone will be only on the shoulder/chamfer of the margin. If this goes up an axial wall then you'll find your fits tight until you ream out the crown
* Yellow CGZ will be what you work out to get your fits ideal. For shallow preps, implants, or preps requiring tighter CG, lower this.
* Blue "add another zone" CGZ is what I use to add additional spacing on the occlusion or incisal for a passive fit (you don't want to grind in the top of an inside of a crown to get it to seat, so I have a larger CGZ if my axial walls are tight). I also use the Blue zone to highlight areas I think will cause troubles, like weird lumps, sharp edges, or undercut areas the software has already blocked out but I want it more blocked out. This extra gap is especially important on implant cases since I want the axial walls tight for anti-rotation, but never want to have to grind out that small space in the occlusion in the internal of the crown.
 
PCdental

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@DAL Claxton and @2thm8kr

My normal crown bottom settings are .07 (axial) and .05 (radial). I just noticed that the setting was .5, not .05. I am an idiot.
 
DAL Claxton

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.5? ouch! Having a half MM would definitely make it a bad fit
 
PCdental

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Of course. I looked at it so many times, just didn't register the missing zero.
 
2thm8kr

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Of course. I looked at it so many times, just didn't register the missing zero.
This is how one becomes an expert with this or any software or anything in general. 😀
 
JMN

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Most of my knowledge came from breaking things and learning how to fix them.
 
RDA

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We haven't had this before. Single central, milled wax up, fit the printed model, but was about two millimeters too long in the mouth. Any ideas?
 
CoolHandLuke

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doc rushed the scan
 
JKraver

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We haven't had this before. Single central, milled wax up, fit the printed model, but was about two millimeters too long in the mouth. Any ideas?
Did it have an opposing tooth? Super eruption? Scan the model the use cut view to check it.
 
F

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Good day all!

I have an IOS I am trying to design, and after I mark the margin, the crown bottom produced is wacky. Does anyone know why this is happening or how I can fix it?

Thank you!
Is this a Itero scan from the Dr or yours? And why are you not marking your margin on a single prep die? Sometimes this happen when a lot of data are too close .
Try a single die it might solve your problem.
 

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