Dealing with Undercuts and Insertion Direction

[sirmorty]

I have recently started doing about 95% of all cases digital.
I like everything about using CAD. It helps to see problems that will come up before the case is even completed.

Unfortunately since the amount of cases has increased so has the problems.

The most common problems I'm coming across are Undercuts that extend past the margin. So when you put on the die spacer option, the Margin is open.


Also the other problems is the Draw of Bridges, I can't get anything that will work with certain cases.


There is no way this bridge can draw



I know you can play around with the Insertion Direction to a certain point and sometimes it helps. I have tried increasing the die spacer.
You can always say Don't Remove Undercuts, but that is just a burden. And not really a solution to the problem.


Has anyone found some workarounds or some tips that I could use to get past these problems?

I'm taking some flack over doing things CAD because the "Old School" would probably just go ahead and start waxing these and then they might be able to get the wax pattern off and get something Cast, But then you are going to have a field day fitting it. I'm trying to work smarter not harder here and that's something some people just don't understand.
Just a little bit frustrated.

 

[rkm rdt]

It's time to make the dreaded phone call.hone:

 

[zero_zero]

When the prep has margin undercuts there's not much to do... except talking to the dentist about proper prepping...
Certain bridge preps support non linear insertion paths, even if it looks undoable... in those cases select individual insertion direction for each prep...

Sent from my SGH-I747M using Tapatalk 2

 

[sirmorty]

Thanks, I guess I'm doing all I can software wise.
Yeah sometimes I do the individual instertion and cross my fingers and hope for the best.

 

[rkm rdt]

If you can show the dr a screen shot then once again the cad software will do the dirty work for you.

 

[Marcusthegladiator CDT]

I had a doctor prepping a 6 unit anterior bridge with a single pontic and he took a quick impression to send me to evaluate for undercuts.
He asked me to put it on the surveyor and mark the undercuts.
Instead I scanned the unsectioned model which had clear margins and gave him screen captures showing the undercut margins.
Then I designed a quick bridge at minimal and milled it out of clear plastic without compensation for the undercuts.
It didn't fit the model but was abrading the areas that clearly needed reduction for a proper insertion path.
I told him if you can get this bridge to fit, then you are in the ball park.

Also, if your milling zirconia for these bridges then it should be easy to explain that a shoulder prep is required for all, all ceramic/porcelain restorations. If the doctor isn't 100 years old, then they should know this. Trying to build all ceramics on a knife edge is asking for failure unless of course your willing to compensate aesthetics for a, "solution."

 

[primus]

On earth, we are bound by the laws of physics.

Maybe you can solve this delima in the 4th dimention in another galaxy?

Dark Matter applications? String Theory perhaps?

 

[primus]

Micro-wormhole to get material into undercut?

I heard Germans are working on the solution.......

 

[rlhhds]

If you can show the dr a screen shot then once again the cad software will do the dirty work for you.

The phone call is not so dreaded with screen shot. I believe it also gives us more cred with the Drs when we can show them stuff like this.

 

[edwarddental]

I'm taking some flack over doing things CAD because the "Old School" would probably just go ahead and start waxing these and then they might be able to get the wax pattern off and get something Cast, But then you are going to have a field day fitting it. I'm trying to work smarter not harder here and that's something some people just don't understand.
Just a little bit frustrated.

As the'' old school '', I can recommend to use cad/cam wax to block out undercuts before scanning.

 

[Marcusthegladiator CDT]

As the'' old school '', I can recommend to use cad/cam wax to block out undercuts before scanning.

Will still have wide open margins. But they'll be sealed with cement right? No problem right?

 

[edwarddental]

Will still have wide open margins. But they'll be sealed with cement right? No problem right?

Yes, How many perfect preps you received today ? All cases was perfect?

 

[Marcusthegladiator CDT]

Yes, How many perfect preps you received today ? All cases was perfect?

LMAO, actually, yes sir. We wont accept anything but. They were all perfect. Nothing but beautiful preps and margins so clear you could have a picnic on the emergence profile.

 

[alphadental]

Marcusthegladietor instead of argue do you have any tips ?

 

[rkm rdt]

There is only one tip here and that is to reduce the undercuts on the dies and to inform the dr!

 

[Marcusthegladiator CDT]

Marcusthegladietor instead of argue do you have any tips ?

Where is this argument your speaking of? Also, I shared my tip earlier in this thread but I would be happy to repost what can bee seen just a few posts ahead.

I had a doctor prepping a 6 unit anterior bridge with a single pontic and he took a quick impression to send me to evaluate for undercuts.
He asked me to put it on the surveyor and mark the undercuts.
Instead I scanned the unsectioned model which had clear margins and gave him screen captures showing the undercut margins.
Then I designed a quick bridge at minimal and milled it out of clear plastic without compensation for the undercuts.
It didn't fit the model but was abrading the areas that clearly needed reduction for a proper insertion path.
I told him if you can get this bridge to fit, then you are in the ball park.

Also, if your milling zirconia for these bridges then it should be easy to explain that a shoulder prep is required for all, all ceramic/porcelain restorations. If the doctor isn't 100 years old, then they should know this. Trying to build all ceramics on a knife edge is asking for failure unless of course your willing to compensate aesthetics for a, "solution."

 

[PinAn]

If you have the 5 axis CNC machine and Sum3d

you can close the undercut function at the interface part

and for the bridge, in the 3 shape , u can insert the another direct way , in the margin part.
of cause , u will need the 4axis or 5axis optimiz in the every direct way at bridge,

maybe you can tell us what CNCmachine and cam software u used.

 

[PinAn]

If you have the 5 axis CNC machine and Sum3d

you can close the undercut function at the interface part

and for the bridge, in the 3 shape , u can insert the another direct way , in the margin part.
of cause , u will need the 4axis or 5axis optimiz in the every direct way at bridge,

maybe you can tell us what CNCmachine and cam software u used.

for explain what i said


then

 

[Drizzt]

The undercut issue have only one cure . Better preps . Even if you manage to mill the crown with the undercut , it will not fit the model . The margin would be smaller than the middle where the undercut usually exists . So you will either have to grind the crown , and open the margin and get to the point you began , or trim the die and tell the doc where to prep the tooth again .

 

[sirmorty]

Yeah, the Individual Insertion works on some cases, I think the most I have got away with is under the 15 degree range, Anything over that and it will be a problem to fit if you can get it to work at all.

I'm outsourcing. So I can't really answer what Milling Machine and CAM software is being used.
I can any control the design process.

Thanks for all the reply's,
I'm glad that there are many people willing to chime in and give their advice.