Apex Dental Materials

Apex Dental Materials

Another problem with the newer systems is that combining primer and adhesive or primer and etch results in primer being applied to enamel. Surpass (Apex Dental Materials) and All-Bond SE (Bisco) are the only newer-generation products Dr. Brucia has found that have no solvent in the adhesive. "I absolutely would never want primer on enamel," he said. "Dentin primer does nothing but get in your way."

The solvent in the primer doesn't allow adhesives to cure. With fourth-generation products, in which the primer, etch, and adhesive are separate, you can remove the solvent by air thinning the primer until the movement of fluid stops. "When you mix primer and adhesive together, no matter how good your technique is, 25% of what you have left is solvent," Dr. Brucia said.

Light also helps remove the solvent, he noted. "If you light assist the evaporation of your primer, your bond strength will routinely go up 20%. I have tested this for years. The added amount of time and heat will give you a much better adhesion," he said.

A problem with sixth-generation products (in which the primer and etch are in one bottle, the adhesive in another) is that the acids aren't as effective for etching, Dr. Brucia said. Five-amino salicylic acid, citric acid, and nitric acid are used because they neutralize themselves in the mouth, eliminating the need for rinsing.

But phosphoric acid is better for etching, Dr. Brucia said. "I use phosphoric acid on everything. If you were to take my phosphoric acid away from me, you might lose a finger."

The differences add up starkly in bench tests, he said. With his fourth-generation OptiBond, PermaQuik, Scotchbond and All-Bond, he can instantly achieve 40 megapascals (MPa) of bond strength, and 72 MPa after 24 hours. By contrast, with the newest products, he can only achieve 10-15 MPa.

As further evidence that fourth-generation products last longer, Dr. Brucia cited an article in Dental Materials (July 2000, Vol. 16:4, pp. 285-291) that found that the "three-step resin adhesive and the RMGIC [resin-modified glass ionomer cement) showed clinically acceptable retention rates, while a high failure rate was registered for the one-bottle adhesive."

"I would still rather have a 12-year-old bonding agent and a 20-year-old composite in my inventory than the newer systems today," Dr. Brucia concluded.

Not everyone agrees that bonding strength has declined with the newer systems. Junichi Ohtsuki, product manager for Kuraray America, acknowledged that seventh-generation adhesives "are not perfect yet." But he insisted that "The sixth generation is the best bonding agent for relieving sensitivity." The fourth generation, he said, "is similar in strength, but it's technique-sensitive."

Asked for evidence to back up his claims, Ohtsuki provided DrBicuspid.com with three articles from peer-reviewed journals. Of theses, one dealt only with the consequence of mistakes in technique. The other two actually supported Dr. Brucia's position. For example, a September 2005 review by Peumans et al in Dental Materials concluded that, compared to fourth generation systems, "The clinical effectiveness of two-step etch-and-rinse adhesives was less favorable, while an inefficient clinical performance was noted for the one-step self-etch adhesives" (September 2005, Vol. 21:9, pp. 864-881).

Ohtsuki also provided a symposium paper speculating on hypothetical advantages of "self-etch" (later than fourth-generation) adhesives. Finally, he supplied two articles from Gordon Christensen's CRA Newsletter, but only one (November/December 2003, Vol. 27:11/12, pp. 1-5) reported tests of a fourth-generation product: All-Bond 2 (Bisco). The anonymous authors gave this product a bond strength of 26.5 ± 6.3 MPa on enamel and 36.1 ± 4.9 MPa on dentin.

These researchers found several other recent-generation products stronger. They rated two fifth-generation products the highest in strength. Prime & Bond NT (Caulk/Dentsply) got the highest enamel bond strength rating (46.3 ± 9.8 MPa), while OptiBond Solo Plus SEP got the highest dentin bond strength rating (59.5 ± 6.9 MPa).

On the other hand, Douglas J. Brown, D.D.S., senior manager for clinical affairs at Bisco, acknowledged that the fourth-generation systems have clear advantages. "The evidence has shown that they are stronger and longer-lasting than the self-etches," he said.

The only advantages to the newest products -- particularly the one-step systems -- are speed and convenience. In some instances, such as placing a restoration in an impatient child, that speed might be worth the loss of durability, Dr. Brown argued.

And even Dr. Brucia acknowledged that in situations in which strength is not at a premium, the newest systems might be useful. Overall, though, he warned that many dentists would pay the price for taking the easy route.

"I'm too busy to have sensitivity," he said. "I'm too busy to have failures."