Questions about bonding

March 1, 2003

Michael Miller, DDS

When restoring an endo 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 (ex. Heliomolar by Ivoclar Vivadent) 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:

  1. 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.
  2. The opaque core of Procera AllCeram should be enough to mask a dark tooth, so the cement should not play a part.
  3. We do not recommend using zinc phosphate.
  4. You can certainly opaque the tooth, but this needs to be done before you take the impression.
  5. 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.
  6. 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.

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Ivoclar Vivadent—

J. Morita US—


Nobel Biocare—