Questions about bonding
based on an article by Michael Miller, DDS
When restoring an endodontic access opening (on an
incisor, for instance) after etching, priming, and placement of a
dual-cure adhesive such as OptiBond Solo Plus (Kerr) with activator, I
will fill the deepest part with a self-cure composite (like Core Paste by
Den-Mat), then add a final layer of a light-cure material (such as Heliomolar) for better wear and esthetics. Will these materials
bond adequately to one another without any interim treatment, or would it
be wise to add a thin layer of adhesive on the Core Paste, cure, then add
the final layer of light-cure material?
They should bond without having to place an adhesive between them.
However, using a thin layer of unfilled resin (not an adhesive) will help
keep the junction between the two materials seamless. After the Core Paste
comes to its initial set, brush on a thin layer of unfilled resin (such as
Heliobond) and brush off the excess. Don't cure this layer. Then fill the
rest of the access with the light-cured material and light cure
thoroughly. The unfilled resin will cure along with the light-cured
restorative material.
I have heard there is some evidence that while self-etching products like
Clearfil SE (J. Morita USA, at right) have good bond strength at 24 and 48
hours, they have shown a big drop in strength at year two as compared to
restorations that are etched with phosphoric acid and regular adhesive. Is
there any truth to this?
Regardless of whether an adhesive is self-etching or not, there is a loss
of bond strength over time through hydrolysis, or so the theory goes. This
is one reason restorations dislodge. While we are not familiar with the
"evidence" you mentioned, we would urge caution when interpreting these
types of results. From a clinical perspective, there have been virtually
no reports of this "mass debonding."
Most in vitro dentin surface preps from the industry are obtained using
fine to sometimes medium grit sandpaper, which results in narrow smear
layers. This makes it easier for these "new" adhesive systems to perform
well for the brochures and even collegiate papers (Tay & Pashley).
However, it may not compare to the coarse burs and thicker smears that
result in the clinical setting. How can we clinicians be sure of long-term
success (not one year, but more like the five to eight years of multistep
systems)?
There is no way to guarantee clinical success based on lab testing, which
can only give you ideas of technique variations and so on. That's why we
don't and have never recommended practicing on the bleeding edge unless
you and your patients understand the potential pitfalls. The issue of
smear layers being much different clinically than they are in the lab
further illustrates the weaknesses of lab testing. However, lab tests do
give us good comparisons of products. If a clinically successful product
and a new product test similarly in the lab, you can at least have a
reasonably strong assumption that the new product will also perform well
clinically.
Does osmotic blistering of adhesives appear if anesthetic with
vasoconstrictor is used and composites are light-cured following standard
clinical protocols? Is there solid evidence that it has clinical
relevance? Does this phenomenon hold true for nonvital teeth and multistep
bonding systems?
The blistering effect as shown by Editorial Team Member Dr. Frank Tay
could have serious clinical implications, but still needs to be
investigated in clinical tests before we should get overly concerned. It
is unknown whether the administration of local anesthesia or the
restoration of pulpless teeth has any effect on this phenomenon.
Multi-component systems are time-tested, but are still not foolproof.
Whether the blistering effect can cause problems with these agents is also
not known.
These issues are timely, but we still believe good, careful calibration of
your procedures will lead to ultimate success in the vast majority of the
cases.
If you choose to mask the tooth with an opaquer before taking the
impression, how would this procedure influence the bond to the permanent
cement, e.g. Panavia (Kuraray America)? Is the bond between the cured
opaquer and the cement good enough?
You need to sandblast the opaquer at the seating appointment, followed by
your adhesive. It is best to use an adhesive that will bond to dry tooth
structure (such as OptiBond FL by Kerr), since your bond strength to the
opaquer will be enhanced if it's dried thoroughly after sandblasting and
etching. Also be sure not to have the opaquer on the margins, all of which
should be on tooth structure. While the bond strength to the opaquer will
not be as high as to tooth structure, it should be adequate.
Which cement do you recommend for Procera (Nobel Biocare, at right)? Could
you use any dual-cure cement or is Panavia F and RelyX Unicem (3M ESPE)
better from a technique point of view (faster, easier to control, and less
bonding steps)? To mask out a dark, nonvital tooth, even the opaque shade
of Panavia is too transparent. Do you have suggestions other than using a
zinc phosphate cement? Would it be possible to place an opaquer on the
tooth without compromising the fit? Is RRGI still banned? I have
understood that ProTec CEM has less expansion than the other RRGI cements.
Would this product be safe for Procera?
Let's take each question separately:
The best cement for Procera AllCeram would be Panavia F or 21. Unicem is
also attractive, but until we have fully tested it, we are urging
restraint. Any of the other dual-cure cements should also work in this
case. Just be sure to Rocatec the inside of the crown.
The opaque core of Procera AllCeram should be enough to mask a dark tooth,
so the cement should not play a part.
We do not recommend using zinc phosphate.
You can certainly opaque the tooth, but this needs to be done before you
take the impression.
While we have not had any recent reports that resin ionomer cements are
still expanding and fracturing metal-free crowns, we still believe resin
cements are the better choice.
ProTec CEM has been discontinued in the U.S. due to poor performance. We
do not recommend it.
Dr. Michael Miller is the publisher of REALITY and REALITY Now,
the information source for esthetic dentistry. You may find information
about these publications on the web at
www2.realityesthetics.com |