Zr Coping Distortion

Rex Kramer

Rex Kramer

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Case has been scanned/designed/milled twice with same results both times on Exocad/Steinbichler (Preciso)

Copings flared open as seen in image below on both CAD scans/designs using settings for scanning implant abutments and default settings. Both times mills came back wide open. Only happened on this case. All other scans/mills have been perfect.


Scanned full arch and dies(abutments) scanned on multi-die plate.

Any ideas on what is happening here?

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eyeloveteeth

eyeloveteeth

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shrinkage rate of zirconia is correct?
 
CoolHandLuke

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shrinkage rate of zirconia is correct?
i'd say its off. looks like it hasn't shrunk at all.

edit: however.

the other cases are fine, apparently. which to me means IF the abuts and crowns were designed at the same time, they were both designed accidentally in the same material; one shrunk, the other did not.
 
CoolHandLuke

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also, its not simply stretched on one direction; the margins probably fit all the way around which means the crowns and abutments were indeed designed originally in the same material. whomever changed their mind at the last minute forgot they'd have to change the other item in the software.

if it wasnt designed at the same time, and these abuts were scanned for crowns after they had been made already, then yes the zr has not shrunk properly. investigate the puck markings and change it in the software. it will be different for each puck, though.

i don't get why you'd be asked to do this though; most cad suites simply output a true-to-life size representation .stl file and the CAM merely grows the file per the shrinkage on the puck.
 
Rex Kramer

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Ok let me clarify further, my apologies. I dont mill, files are outsourced to a milling center. Abutments done using NobelProcera system so I scanned them separately.
How the copings fit, all 'rock' on abutments, oneside will close but not the other, like they are too big.

Can scan data get distorted somehow? My first attempt was submitted with several other copings (1 an implant abutment scan) and those all fit fine. Something about this case. Full arch scanning then multiplate die scanning of abutments?
 
CoolHandLuke

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you sent all the files to the same place but only this case of the batch was off?

then the zirconia shrank just fine, and the scan was not done correctly. compare this case scan settings vs the other cases. you should notice a difference.
 
Rex Kramer

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Yes, if you look in the images above this I scanned/submitted this case twice, 1st with modified settings I do for implant abutment scans and then a second time with default settings I use for regular copings and both sets came back looking like above. So its confusing the crap out of me why just this case. And Im not drinking yet...
 
CoolHandLuke

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what about the other cases, the ones you said came back fine. what settings of those are different from the ones above?
 
Rex Kramer

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what about the other cases, the ones you said came back fine. what settings of those are different from the ones above?

Yea 2 where default setting and the 3rd other case was the implant settings and they fit so you can see why Im confused what this could be, multiple abutments in multiplate die holder. I was thinking I may have switched positions some how but verified that was not the case on the second go around.

But hey thanks for trying help. Ive already started PFMs on these NicelyMKV so no need to mill again but yea thanks for the offer!
 
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edwarddental

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Rex, send same files to another milling center and see if any difference . if it is - problem at the milling center during the sintering . Happen to me few times .
 
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Another way this can happen is if you aren't careful about your insertion axis. The software is designed to block out undercuts. If the chosen insertion axis has an undercut going across the margin line the software will block out that undercut and open up the margin area. First thing I would check (before sending to another milling center) is the design of the copings. If you have uncut going across the margin line, the software did what it is supposed to do and blocked out the die.
 
CoolHandLuke

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Yes, if you look in the images above this I scanned/submitted this case twice, 1st with modified settings I do for implant abutment scans and then a second time with default settings I use for regular copings and both sets came back looking like above. So its confusing the crap out of me why just this case. And Im not drinking yet...
rex, comparing the two scans to themselves isnt going to tell you where the sliders were set wrong.

open one of the other cases that fit correctly, take pictures of those settings and compare with your bad case. maybe you moved the wrong slider by accident.
 
cadfan

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Shrinkage rate wrong let them mill out one twice in pmma or wax or scan the inside and load as situ model so you can see if their are big differences btw. your modellation and zi copings


Look at your parameters end of cement gap is 1 mm not zero

dont block out the same
 
Rex Kramer

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Scans I've gotten back post this case are all fitting just fine. Went back and looked at all settings and everything there is fine, Im thinking that barring a shrinkage issue (which seems unlikely that it would happen twice and only on the same case) that somehow the software looked at these 3 crowns as connected for purposes of path of insertion as MFerg has suggested above regarding insertion angle, right now its the only thing that makes sense to me. I dont know
 
cadfan

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Hi Rex my mistake your settings are right the only thing i would change is the last parameter dont block out, not zero but 1 mm so the margins are never open because of different insertion axis. If you scan the inside of the crown and load it in your case as situ for example and registrate it first with a few points than best fit you see what happened shrinkage or block out insertion angle.Both stl the constructed and milled must have the same size if yes insertion ax was wrong if no shrinkage faktor was wrong, this can although be use if you have two impressions ( modells) and its not clear which is better to check the margins digital.
 
Rex Kramer

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.... If you scan the inside of the crown and load it in your case as situ for example and registrate it first with a few points than best fit you see what happened shrinkage or block out insertion angle.Both stl the constructed and milled must have the same size if yes insertion ax was wrong if no shrinkage faktor was wrong, this can although be use if you have two impressions ( modells) and its not clear which is better to check the margins digital.


Now this is interesting, I didnt know this was possible to do with Exocad and first chance Im going to look at that. I have no idea how to do this though. But as a scan/design lab only this would be a fantastic method for troubleshooting.

Thanks
 
Marcusthegladiator CDT

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That's a good idea. Pour up the inside of the crown with duralay... make some references for future stitching references... scan as situ and see how the meshes overlap....
 
DMC

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Have case milled in PMMA or Wax-printed.

It is probably your scan data.

Something moved during scanning I would bet.

How are you holding your work in the scanner?

Doubt it was anything mentioned above.

Sagemax is not the answer! LOL
 
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