Page 68 - CEREC Q4|2012
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d i s c u s s i o n f o r u m
I find that being close to the tissue gives really nice
margins, even if I think it doesn't look smooth on the screen.
Also, try marginating those cases from a 45-degree angle
visually; it seems to help delineate the spot you want to
mark.
Justin Gates | Marion, Virginia
[In response to Kent Mosby]
I had this issue at the
beginning. If you can eliminate everything else
that has been posted above, let me suggest one: it’s the prep!
Look in the first and last picture. It’s really not bad at all, it
just needed 45 secondsmore refinement. I amnot one to crit-
icize, but you asked for the help. It needed a slight roll over
on the cusps (functional cusp bevel or two plane reduction).
It looks like there are some sharper small irregularities at the
buccal or lingual/occlusal line angle.
The MCXL is supposed to overmill and allow for these
sharper irregularities in the prep and still seat, but some-
times it’s not enough overmill. Any sharpness or jaggedness
at any line angle causes a problem when seating. Before I
started rounding all the occlusal line angles more than
normal lab-driven crown preps, I would have this same "not
seating fully" issue. If you would have adjusted the internal
aspect of the crown in the area that you see in picture 3/4
on Kent’s reply, or smoothed the cusps seen in picture 1,
you would get rid of the problem. I hope this helps. Again,
I think the comments by Kent are spot-on for the margin-
ation and Kurt’s are also helpful. Use the parameters to
help bulk out the margin and then trim/thin it back slightly
when adjusting in the purple state.
One suggestion that I use tohelpme see these issues earlier
before I image: after I have prepped and think that I amready
to image, I let one of my DAs take the opposing and buccal
bite images/scans. Then, when I scan the prep arch and
marginate, I reevaluate the prep before scanning. Then you
can make a minor adjustment if needed. My DAs never take
a buccal bite with the prep in it, so it doesn't affect stitching.
P.S. I have re-looked at more than a few of my preps that
I thought were great and realized they were missing just
slight refinements to allow for faster appointments, which
equals easier and more fun appointments.
Mark Dunayer | West Nyack, N.Y.
FirstweekwithCEREC(Omnicam), soI'mreading
about polishing prep and margins. What specific
burs or stones are in use to get "Porsche-like" smooth preps?
Gregor Sonin | Potsdam, Germany
I use these:
6334&L=1. The burs work perfect. All I am
adding to the final prep is a quick polishwith a brownie. But
leave the margins alone, only low RPM with the red burs
from the kit there.
Mike Skramstad (Faculty)
I like the fine-end cutting diamonds from Axis.
Gregory Mark | Forest Hills, N.Y.
[In response to Mark Dunayer]
I use KS6 or KS0
fine, 10 RPM.
Robert Marcus | Poway, Calif.
[In response to Mike Skramstad (Faculty)]
I couldn't agree more with this. Ever since I
switched exclusively to the 12 (non-S) burs, I have been
having way-better-fitting restorations. I do understand
that they don't last as long as the 12S burs, but I'm willing
to deal with that.
Mark Dunayer
10 RPM?
Gregory Mark
[In response to Mark Dunayer]
10 RPM on elec-
tric high speed, or 20 RPM #2 carbide bur on
electric slow speed.
Robert Marcus
[In response to Kevin Potts]
On my Bluecam I use
120 spacer. I raised it to 140 on Omni. Seems to
seat better but still tight.
James Kim | Tucker, Ga.
[In response to Mike Skramstad (Faculty)]
Is this
what most mentors do?
