mill PMMA for casting

[Gita]

Anyone mill PMMA for casting? Which CAD/CAM system u use? Any problem?
Thanks..
-gita-

 

[BobCDT]

We have tried to mill PMMA for casting.
Wax works much better. Why do you want to kill and cast PMMA?
The nice thing about wax is the ease of use after milling in the analog environment. PMMA is far more difficult to add to or correct a margin.
Bob

 

[NicelyMKV]

I have to do three stage burnout with PMMA as well.

 

[RJS8669]

My issue with milling PMMA for casting had to do with drill compensation. What appears to be ample space turns out not to be so much...

 

[CoolHandLuke]

with PMMA you will need to adjust your die spacer to about 3x the normal size, mostly due to material shrinkage. if you have a mill that accomodates a shrinkage factor for each puck, and expands designs by that factor, then when you make PMMA pucks try making the shrinkage factor 1.002 and using only double the die spacer.

yes it is tougher to burn out a pmma coping, but for the stability of a margin that was designed properly in the first place, it is beneficial. mostly this is for knife edge margins, or long shoulder preps / high linguals or other sharp edges.

for full contour it doesnt too much matter if you do PMMA or Wax milling. mostly though wax is cheaper and not so tricky on a dry mill, as extended milling times can snap tools when you do PMMA.

 

[SpyGr]

Guys, do you know the casting parameters of PMMA ? I have milled a partial denture in PMMA in order to cast it. What are the casting parameters for this ?

I didnt see in my CAM software to set shrinkage factor for PMMA (SUM3D) , I have milled it ordinary as we do with wax.


What things I have to know before cast it? Any advises or precautions ?


Thank you in advance

 

[SpyGr]

Also if anyone know burnout stages with melting point and holding times I would be grateful