7 things you may not know about universal adhesives

Since its inception in 1955 when Dr. Michael Buonocore first discovered that you could adhere to enamel using acid, adhesive dentistry has changed the way dentists treat patients. However, while Buonocore’s findings serve as the basis of adhesive dentistry, much of the science has changed. Moreover, advances have made adhesive dentistry more streamlined.

Dr. Daniel Poticny, DDS, who practices in Grand Prairie, Texas, explains that cementum, dentin and enamel bond differently. Enamel bonds are durable while dentin bonds may start strong but can weaken with time. Cementum bonds, on the other hand, are notoriously poor because their structure doesn’t lend itself well to adhesion.

The gold standard for adhesives resides with the “fourth-generation” products using three bottles (acid+primer+adhesive), regarded as difficult to use but that yield the best overall performance. Subsequent generations five through seven simplified things yet yielded mixed results.

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A new category of adhesives now exist that transcends the generational approach. Dr. Poticny believes universal adhesives are in a class of their own, with efficacy that rivals the fourth-generation adhesives but without the complicated procedures. “Doctors would be well served to strongly consider the use of universal adhesives today,” Dr. Poticny says.

Dr. John Burgess, DDS, MS, and dean of clinical research at the University of Alabama at Birmingham, agrees that dentists should use universals. “When you get to second- and three-year recalls on a material and you're getting great results, this is very good material.”

Universal adhesives can be used with the self-etch, selective-etch and total-etch bonding technique. The adhesive MDP monomer contained in most universal adhesives enables effective bonding to calcium, dentin, enamel, zirconia and metal alloys.

But there are some important facts that many dentists might not know about universal adhesives. Our experts shared their expertise about these versatile and efficient materials, including these seven things you probably didn’t know about universal adhesives.

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#1: The first universal adhesive has a 100% retention rate after three years with a total-etch approach.

Universal materials were introduced in 2012. Dr. Poticny says he has used universals since then and believes his own observations agree well with the controlled clinical and in-vitro data generated over nearly five years.

Scotchbond Universal from 3M was the first universal adhesive introduced. “It has the 10 MDP Monomer [10-Methacryloyloxydecyl dihydrogen phosphate], an adhesive phosphoester monomer, so that particular adhesive monomer bonds the adhesive directly to the calcium and to zirconia and other materials, particularly base metal alloys,” Dr. Burgess says.

Dr. Burgess and his team are working on the 5-year recalls for Scotchbond Universal used in a total-etch and self-etch mode. While those results are not yet available, the 3-year recalls had a 100 percent retention rate using the total-etch technique. Retention dropped to 94 percent with self-etch, and there was more leakage around the restoration. Dr. Burgess recommends using either total-etch or selective-etch approaches when using universal adhesives, not only because of the improved retention, but also due to the decreased marginal staining around restorations using the total-etch technique.

#2: Universal adhesives have a higher pH level than other adhesives.

Phosphoric acid etches enamel well and, as Dr. Poticny says, “enamel likes an aggressive etch.” In the generations of adhesives, pH has been a factor for bond strengths. In particular, the self-etchers had challenges with bond strength.

“They later discovered that was because the acid was weaker in the self-etchers, it was also a weaker bond to the enamel,” Dr. Poticny says. While the mild etch pattern was good for the dentin, it was poor for the enamel. “There were tradeoffs,” he says.

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The pH of phosphoric acid ranges from .3 to .4. The pH of the primers ranges from .7 to 2. Dr. Burgess explains that universal adhesives have a pH of 2.3 to 3.2, so they won’t etch enamel as well as phosphoric acid and should be used with a selective or total-etch technique.

#3: The application techniques are simplified with universal adhesives.

Universal adhesives work with direct and indirect restorations, desensitization, sealants and restoration repairs. Universal adhesives also allow separate etching of the enamel (unlike self-etch-only products) without compromising bonds to dentin. Moreover, universal adhesives achieve high bond strengths to enamel in comparison to the self-etchers.

“It's got everything in it,” Dr. Poticny says. “Simply put, it will enable bonding to virtually any substrate or material with exception to high noble metals. Dentists can throw all this other stuff away that they've got in their office. And because there's only one system that you need to know, it's easy to repeat the same technique every time.”

Bonding is an active process, so agitation is still necessary. But since universal adhesives are filled materials (from 4 to 8 percent), a reliable bond will develop even with fewer applications.

“With older generation adhesives, at least two applications were needed to develop an adequate bond. With universal adhesives, one single application seems to be adequate,” Dr. Burgess says.

“The biggest thing for me is streamlining workflows and reducing the number of adhesive systems needed while improving consistency and outcomes,” Dr. Poticny says. “I've been in hundreds of dental offices over the years and watched doctors operate. Typically, they inventory three adhesive systems or more depending on the dental procedure.  This is costly. It also requires familiarity with numerous products and their use, as well as the need to monitor inventory for expiration and the like.  Just remembering instructions alone can be a challenge.  Either way, one system makes sense if outcomes are not compromised.”

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#4: Your curing light matters-a lot.

Dr. Burgess says that a good curing light is essential for excellence in adhesive dentistry and recommends placing the light as close to the tooth as possible, preventing movement of the light guide and then curing it. Furthermore, he also suggests directing an air stream over the end of the light guide if you are close to the pulp when curing.

“That dissipates the heat that's being generated in your curing light,” he says.

He also advises frequent tests of the curing light.

“If the curing light has been dropped, take the light guide and put it on newspaper print. If the print is displaying accurately on the end of the light guide that is visible, then you know that the light guide is not fractured along its length. These light guides run from $120 to $180, so don't replace them capriciously. But at the same time, you want to replace them when they are chipped or fractured because that diminishes light output,” Dr. Burgess explains.

#5: Universals are much more resistant to contamination than their predecessors.

The fourth generation, two-bottle, total-etch systems were susceptible to contamination because of their longer application times and multiple steps for each application. Contamination lowers the bond strength of all adhesive systems, but older two-bottle, total-etch systems are more prone to contamination. Dr. Burgess and his team have worked with Clearfil Universal and the Scotchbond Universal adhesives and noted that with the shorter application time, the window for contamination for these materials is significantly shorter.

“Even though the bond strength may not be quite as high as with some of the fourth-generation materials, clinical success seems to be better because the universal adhesives can be applied quickly (with fewer steps), reducing the negative effects of contamination,” explains Dr. Burgess.

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Dr. Poticny agrees, saying, “Doctors would do well to investigate universal adhesives from any one of the reputable manufacturers. They tend to be a little bit different, but they're all designed with the same intent in mind. Could you give something up in the way of bonds? Yeah, but I don't think it's clinically significant today. They're that close in performance to the Gen 4 materials.”

#6: Universals have a separate bonding mechanism in addition to the hybrid layer formation.

All bonding agents create a hybrid layer consisting of collagen encased adhesive. Total-etch hybrid layers are thicker and more consistent than self-etch hybrid layers. However, Dr. Burgess explains that universal systems have a separate bonding mechanism by creating a chemical bond from the 10 MDP monomers to the calcium in the tooth. This makes the bond more durable-and getting more so all the time.

“We're looking forward to another generation of adhesives that is even a greater breakthrough,” he says.

#7: Most universals bond well to zirconia.

Doctors now bond not only to teeth but also to materials, like glass containing ceramics (feldspathetic porcelain and lithium disilicate) and zirconia, a high-strength ceramic.

“So, if want to bond to an alloy or glass, you've got to have a separate chemical to treat the glass, which is silane for glass ceramics and metal primers for metals. You've got to get those bottles out. You've got to put this in, do that, everybody's got to be in sync. It got complicated,” Dr. Poticny explains. “Product dependent, universal adhesives simplify this.”

Scotchbond Universal contains the 10 MDP Monomer bond, which creates a strong bond to zirconia without any other primer.  With traditional zirconia, the dentists would sand blast the intaglio surface and then apply the universal adhesive directly, providing a strong bond, particularly when using the RelyX Ultimate cement. Prime and Bond Elect is an excellent universal adhesive that uses Penta as its adhesive monomer. Dr. Burgess explains that Penta is excellent for bonding to teeth but a separate application of the 10 MDP monomer (Z Prime – BISCO) is needed for bonding to zirconia.