Page 70 - CEREC Q2 | 2014

68 | CERECDOCTORS.COM | QUARTER 2 | 2014
on the material and the strength of HF you have. e.max is
30 seconds with 5 percent, and 13 seconds with 9.9 percent.
Double those times for all other ceramics; do not etch Zirc.
Follow the instructions to the letter formixing and applying
the adhesive system of choice. Use a timer when applying
materials. Donot assume your assistant has any ideawhat they
are supposed to be doing; do not cross-contaminate brushes if
usingmulti-bottle systems; beparanoidaboutwater in the a/w
syringe. By the way, in my own personal experience we had a
problemwith water built up in the air lines. There are dryers
available to fix this. We also had an oil issue (as noted above).
Even with dry air, I have seen water come out of the syringe,
so I always start the air pointedout of themouth to clearwater
fromthe tip then come into themouth to dry or thin.
It is critical that there is no movement of the crown while
the resin is setting up. You need to hold it down firmlywhile
cleaning excess (a finger or an instrument work great). Hold
it in place until you are ready to cure the resin, then hit it
with the light before you let off the pressure. If the crown
lifts while the cement is partially cured, it will not set prop-
erly. Make sure you are final-curing the resin cement. The
time it takes to fullyautocuremayallowfor somemovement.
I do not keep my adhesives and resin cements in the
fridge. I go through them fast enough to not worry about
it, and I do not want slower chemical reactions.
Make sure the assistant is shaking the bottles before
use, and capping them immediately after. Do not dispense
materials way in advance.
Most importantly, I think you should have a trainer in
your office to go through everythingwith you and see if the
error can be isolated.
One last thing, do not mix systems unless you have
researched it thoroughly. You indicated that you were using
UnicemwithMultilink. I assume youmeant the A-B liquids. I
am not aware that these two completely different systems are
in any way compatible. Additionally, in my opinion, Unicem
is a poor adhesive resin cement. It should only be used with
conventional retention crowns. Stay within a system to avoid
chemistry issues. The Unicem instructions are to etch, then
apply silane. No adhesive, etc. Iwould even be concernedwith
Monobond, as Ivoclar has added a resin component nowand I
do not know if therewould be an interactionwith theUnicem.
Rich Rosenblatt (Faculty)
Right there is why this site never ceases to
amaze me. Awesome, Marc!
| | | D I S C U S S I O N F O R U M
I think it would be beneficial for you to have someone
come in and watch what is going on, but in the meantime,
let’s go back to basics. The most important thing will be to
not deviate from the written instructions for the adhesive,
and do not be creative in finding a solution.
I am going to list every source of error I can think of:
Oil contamination of the prep or crown. Are your
handpieces purged prior to use? Are there oils in your
compressed air? This occurs with older compressors over
time, and can be corrected by a technician. Oil builds up in
the compressor tank and gets into the lines.
Polishing the preps too much may reduce some micro
mechanical retention, so frankly I would not worry about
this. I have always left the majority of my prep with a
mediumor course bur finish on it. Refine your margins and
smooth off any sharp line and call it good.
On a posterior tooth, leave some vertical wall height
somewhere for a touch of resistance form. If nothing else,
it makes it easier to accurately seat the restoration.
I do not know about studies showing zero bonding effect
from powder residue, but I do not want all the dentin
tubules potentially plugged up with powder, or a bunch of
powder mixed into my adhesive layer. The reason it is hard
to clean off is a combination of an adhesive and that the
powder gets bound up in the salivary proteins which bind
to the tooth. Clean this all off right after imaging. Consepsis
does a good job with this, and Total-etch does a great job
with this, although youmay slightly decrease bond strength
with Multilink. I Total-etched for my entire career before
CEREC, and while using Bluecam. I never had a bonding
problem, and I have never had a large sensitivity issue. Etch
was the quickest, most predictable way for me to get rid of
powder. Less of an issue nowwith Omni.
Do not use peroxide on a prep, ever. It will dissolve
oxygen into the teeth which then out-gasses for a while.
The oxygen inhibits the adhesive. It also affects the set of
PVS. Superoxal was touted as a great hemostatic back in
the bondodontist days of Ray Bertolotti. It is great for that,
but the impressions would not always set at the margins.
You need to move to a same-day crown protocol. The
dentin bond is never as good as same-day and, frankly, you
are missing the point of CEREC by adding the overhead
expense and time-waster of a second seating appointment.
Do not sandblast the crown; there is no need for this and,
in fact, you are weakening the crown by doing so. Sandblast
in the mouth is a mess and not worth the effort and clean
up. Etch the crown with HF for the appropriate time based