Old-style adhesives are better, researcher says

Old-style adhesives are better, researcher says

Violins, cathedrals, waffle irons: they don't make 'em like they used to. To that list, Jeff Brucia, D.D.S., co-director of the Foundation for Advanced Continuing Education (FACE), would add dental adhesives.

"Apply the technique of the 1970s," Dr. Brucia told an audience of 400 at the recent ADA annual meeting. "It's not the coolest. It just works."

One goal of the seminar, titled "Restorative Materials Update 2008," was to review "new advancements" in restorative dentistry. But according to Dr. Brucia, there have been precious few advancements for the past few decades -- especially in bonding systems.

"There has not been an improvement," he said. "There has been a different mode of application." In fact, many products and techniques being used today are not as good as those Dr. Brucia's father used, he said. "He never had sensitivity. Why weren't his restorations falling off? Why are ours falling off today?"

Three adhesive makers contacted by DrBicuspid.com -- Ultradent, Bisco, and Kuraray America -- offered varied reactions to Dr. Brucia's observations: a Kuraray spokesperson disagreed, an Ultradent spokesperson declined to comment, and a Bisco spokesperson mostly agreed.

The problem with mixing

Dr. Brucia, who inherited his father's San Francisco practice and is a University of the Pacific assistant professor, has also been paid to lecture to some adhesive companies. But he said he's beholden to none -- and often contradicts them. "The companies don't like me," he said.

One reason is that he insists the art of bonding reached its zenith with what is now called the fourth generation. This system requires three bottles: an etch, a primer, and an adhesive.

The etch is phosphoric acid. The primer is a hydrophilic agent designed to bind well with dentin. The adhesive is a hydrophobic agent that binds well with porcelain and composite.

Examples include All-Bond 2 and 3 (Bisco), Bond-It (Pentron), OptiBond FL (Kerr), Syntac (Vivadent), Scotchbond Multi-Purpose Plus (3M), and PermaQuik (Ultradent). "They work," said Dr. Brucia. "They work. They work really, really, really well."

Subsequent systems have not shown the same bond strength, Dr. Brucia said, citing both his own lab tests and published studies.

Fifth-generation adhesive systems attempt to save a step by combining primer and adhesives in the same bottle. "How do you take something that loves water and put it together with something that hates water?" Dr. Brucia asked. "You make the product very acidic."

He compared the notion to combining shampoo and conditioner in one. Sure, it's more convenient, he said, but it doesn't work as well. "Give me a fifth-generation system and I have to concentrate like no tomorrow to make that stuff work well," he said. "If I make a mistake with this product, I get catastrophic results."

One problem, he said, is that this acidic hydrophilic bonding agent can cause an acid-base reaction when it comes in contact with a dual- or self-cured composite. Unless the composite is cured within two minutes of placement, this reaction can prevent it from ever curing. Another problem is that the acidic hydrophilic bonding agent creates osmotic blistering.

As evidence, Dr. Brucia cited research by Indiana University researchers (Operative Dentistry, May-June 2006, Vol. 31:3, pp. 346-353) that found that later-generation bonding systems were more water permeable.

To cope with these problems, various adhesive companies introduced new materials to add to the restorations in the late 1990s, Dr. Brucia said, but none worked. Later innovations haven't helped much either, he added. "If you go down to the exhibit floor, they'll tell you, 'We've fixed it.' Well, why did [they] break it in the first place?"

More recently, adhesive companies began raising the pH in their products. "I shook my head," said Dr. Brucia. "I said, 'Wait. We needed the acidity to keep the hydrophilic and the hydrophobic products together." And sure enough, research showed that the new products weren't very stable.

Lack of stability particularly plagues the seventh-generation systems, in which etch, primer, and adhesive are all combined in a single bottle, he said, citing a study in the American Journal of Dentistry (April 2006, Vol. 19:2; pp. 111-114).

The single-bottle products are so unstable that they have to be kept chilled. "When we're doing a study, we call up the company and ask if we can get some of the product," Dr. Brucia said. "It arrives packed in ice." But adhesives makers often neglect to inform their customers of this problem. "When is the last time you bought a bonding agent and it came packed in ice?"