Milling Wax - How do you avoid open margins?

[NickB]

Hey all.....we finally got the rocking issue solved on our milled wax. Large bridges would fit great in wax, yet rock once cast. We finally got that solved. Now another problem.....

We usually have big full arch bridges, and the doctors often leave undercuts on the posterior preps. We mill the bridge and obviously we know its going to mill the margin and leave it open. Anyone else have this problem and how to avoid it? We rotate point of insertion to try and minimize the open margins, and sometimes that works, but other times the prep is so badly undercut that we simply have to reduce the prep after its been scanned.

Just wondering if any of you guys had any tips or can tell how you go about avoiding this problem.

Nick -GA

 

[RileyS]

how about reducing the prep in the digital software? That way it won't have to mill off the margin. Then you adjust the physical die to match.

 

[NickB]

how about reducing the prep in the digital software? That way it won't have to mill off the margin. Then you adjust the physical die to match.

F'ing sweet idea! I knew about the die adjustment in the software, but forgot about it. Thanks for the reminder!

 

[Joe]

why don't you reduce the prep before you scan the case? Or, scan, check for undercuts, reduce prep according to what you see on the screen, and rescan the die? Or, mill with a 5 axis strategy so it doesn't leave the margins open, cast it, then bash it onto the die. You know, old school crown and bridge.

 

[Sevan P]

In 3shape just uncheck remove undercuts in the die spacer section, this will close the margin, then mill, invest and cast, then fit it to the die and adjust as needed. Not the best way to do it but it will work. But this will effect the thickness of the unit near the margin. Tell your docs to try 1% harder, it sad we have to cover their asses for them. But i guess that's the way it goes.