Crown Bottoms over Ti Bases

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Labslip

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Hi All. Long time lurker forced out of hiding.

When creating crown bottoms over Ti Bases in Exocad I’m having trouble getting a tight enough fit. My cement gap is set to zero as is my axial spacing, but the fit is still looser than I would like. I used to set the Axial spacing to a negative number and get good fits but with the Galway build it creates a wacky shape that doesn’t fit.

My reseller has been of little help so I’ve been forced out of my lurker’s hideaway.

Any ideas?
 
CoolHandLuke

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sounds like your mill is overmilling by default.
 
Tayebdental

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You mean the zirconia crowns fit over ti bases? It could be incorrect zirconia shrinkage rate also.
 
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You mean the zirconia crowns fit over ti bases? It could be incorrect zirconia shrinkage rate also.
Yes, the fit of zirconia crowns over Ti bases is too loose resulting in wobbly crowns. The shrinkage rate of the zi pucks is input for each puck according to the manufacturer's specs.
 
zero_zero

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Just scale down the implant base file a bit, problem solved
 
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Just scale down the implant base file a bit, problem solved
Could you be more specific?
The cement gap in the Material Configuration won't go below zero. There's probably a way to unlock it and re-set the minimum but I don't know how to do it. The additional axial spacing is also set to zero. I can set the axial spacing to below zero but that creates a crown that just doesn't fit. It's not a matter of tight or loose, it has odd shapes.
 
zero_zero

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I was talking about the actual file to be scaled down, not possible with settings
 
AGV

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Ti base scanned or library Ti base??
 
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I was talking about the actual file to be scaled down, not possible with settings
Is that something I could do with my existing software or would I need to use another program like Meshmixer?
 
zero_zero

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Meshmixer should work
 
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Labslip

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Meshmixer should work
I've never used Meshmixer or any other non-dental design programs and was hoping I could solve my problem with the software I already have. It's hard to imagine I'm the only one having this issue.
Anyway, thank you for the response. I appreciate it.
 
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FASTFNGR

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Hi All. Long time lurker forced out of hiding.

When creating crown bottoms over Ti Bases in Exocad I’m having trouble getting a tight enough fit. My cement gap is set to zero as is my axial spacing, but the fit is still looser than I would like. I used to set the Axial spacing to a negative number and get good fits but with the Galway build it creates a wacky shape that doesn’t fit.

My reseller has been of little help so I’ve been forced out of my lurker’s hideaway.

Any ideas?
Does the TI base completely round or it has a straight edge? If it does not it is preferable that you do it. Does your TI has a straight color? I alway make sure mine is up and down and flat edge to make sure it does not turn, and that cures it.
I am thinking also that you are spraying too to be able to scan it? That adds more spacing.
 
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I had that problem - was using Straumann to bases and rotational fit was always too loose. Similar setup with Exocad, millbox, and Roland mills. Exocad was fine (Straumann locks their library so fit couldn’t be adjusted…) but I found that in millbox, I had to shrink the fitting surfaces by about 0.020 mm or something like that to get the tighter fit. In my case I had to actually go into the settings of millbox and add a greater internal reduction value than what was standardly available.

I will say during the process I had blamed Exocad, the zirconia, and the sintering oven … finally was able to fix it with that one setting in millbox when nesting the file. Hope that helps!
 
apostolis159

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Why are you scanning the ti-bases instead of using scanbodies & implant libraries? You would get a much better cement gap and the fit will be waaaay more precise.

I just realised you mentioned this:
The fits are the same whether I'm scanning the base or using a library.
Your problem seems to be mill-related and not exocad related.
Do you have problems with normal crowns (not on implants/ti-bases)?
Have you called your mill/cam reseller/support? Do they have any ideas?
 
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I will say during the process I had blamed Exocad, the zirconia, and the sintering oven … finally was able to fix it with that one setting in millbox when nesting the file. Hope that helps!
Interesting. Let me get this straight.
In Millbox you are going to Tools - Shrinkage Factor. What they call the Uniform Shrinkage Factor is the shrinkage factor number that I input when adding a new disc. You're suggesting I change the shrinkage for this particular unit. For instance a puck has a factor of 1.227, I'll change it to 1.207 or whatever to mill this implant crown.
 
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Why are you scanning the ti-bases instead of using scanbodies & implant libraries? You would get a much better cement gap and the fit will be waaaay more precise.

I just realised you mentioned this:

Your problem seems to be mill-related and not exocad related.
Do you have problems with normal crowns (not on implants/ti-bases)?
Have you called your mill/cam reseller/support? Do they have any ideas?
In my case they are not waaaaaay more precise. In fact the fits are way more mediocre. I get a more precise fit by scanning the ti-bases than I do using the scan flags. My preference is to use the scan flags but I have been unable to dial in the fits.
Normal crown fits are excellent.
My re-seller has been unhelpful, that's why I'm tapping into this source of unlimited knowledge.
 
sidesh0wb0b

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In my case they are not waaaaaay more precise. In fact the fits are way more mediocre. I get a more precise fit by scanning the ti-bases than I do using the scan flags. My preference is to use the scan flags but I have been unable to dial in the fits.
Normal crown fits are excellent.
My re-seller has been unhelpful, that's why I'm tapping into this source of unlimited knowledge.
try slightly adjusting your milling diameter anticipation down some. ;) depending on your tool setup youre probably somewhere around 1.2mm
reducing it some should get you a more snug fit, and only do this for those implants
 
Affinity

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Sounds like its overmilling with the large diameter bur and then making it worse with the 1mm. What size burs are you using? Cheap tools?
Like bob said, look for 'anticipate milling diameter' option in exocad. Not familiar with millbox but every CAM imports the abutment geometry differently, some even lock them :banghead:
 
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