Are universal adhesives truly universal?

A “one-stop-shop, magic bullet for all your dental adhesive needs,” was the promise heralded with the introduction of universal adhesives. Although these versatile adhesives can bond to a wide variety of materials-including glass ceramics, zirconia, lithium disilicate, and composites—are they really the right choice for every situation? Are they, in essence, truly universal?

They certainly seem to be at first glance. Since universal adhesives will bond to so many different materials, it gives them broader applications than previous generations of bonding agents. Generally defined as one-bottle systems that don’t require mixing, they are an etchant, primer, and bonding agent all in one. They can be used with self-etch to total-etch protocols on dentin or enamel, and are compatible with light-, self-, or dual-cure composites. In short, they are a comprehensive product that offers convenient solutions that simplify procedures while saving time and money-all without compromising on bond strength.

“The newer universals are definitely less technique sensitive and they really set the stage for making procedures simpler,” says Dr. Jeff Lineberry, a general dentist practicing in Mooresville, North Carolina. “But you should always consider the clinical indications before making a choice.”

Simpler Doesn’t Always Mean Better

"For me, I’ve always said I believe that the best approach is a tailored approach to each clinical situation,” says Dr. Jason Goodchild, director of clinical affairs at Premier Dental. “For instance, if there’s enamel, I want to etch it. If it is dentin, I usually don’t want to etch it. So, having a product that can do everything is great. But I also [believe] a lot of dentists think ‘I’ve got to have multiple bonding agents,’ so you see dentists with a drawer full of bonding agents. And it’s not necessarily a bad thing to have different options for different indications.”

What Universals Bring to the Table

While previous generations of bonding agents also combined etching, priming, and bonding, universals were developed with a focus on increased bond strength. This is bolstered by the 10-MDP (methacryloyloxy-decyl-dihydrogen-phosphate) monomer, which serves as the primary adhesive in universals, as it is very hydrophobic. Hydrophobic materials are less susceptible to problems that arise from moisture—and, since water is a big contributor to bond failure, this gives universal adhesives a leg up over previous generations.

The 10-MDP also contributes to universals’ ability to bond to a wide range of materials. This versatility means they can be used in a variety of clinical situations, while also simplifying inventory. The ease of use provided by fewer bottles and less mixing is unparalleled, which leads to more streamlined procedures.

Because universals only require one application, they are also more resistant to contamination than previous generations. Systems like the fourth-generation offerings (which were two-bottle, total-etch systems) took longer due to the multiple steps required for application. This leads to an increased window for contamination that can lead to adhesive failure.

Essentially, universal adhesives offer increased bond strength-to numerous materials-with reduced procedure time. They are indisputably a great, efficient addition to any dentist’s arsenal. But while universal adhesives have many applications, are they really universally indicated?

“I don’t think there’s a particular set situation where you couldn’t use a universal, but there are things to take into consideration,” Dr. Lineberry says. “For instance, when I’m bonding veneers in place, I don’t want something that’s going to be thick, which can happen with some universals. So, I’m very conscientious of the overall thickness and the viscosity of the material. That’s really one thing that I think about.”

“I also avoid universals when I’m bonding temporary veneers in place,” Dr. Lineberry continues. “One technique we use is spot etch, so some people will coat the preps with an older-generation bonding agent that obviously doesn’t have self etchant in it.”

Clinicians should always take etching into account when deciding on universal adhesives. Several studies have reported that, when bonding to enamel, universal adhesives have better bond strength when first etched with phosphoric acid.¹ Since universals are less acidic and have a lower pH than prior generations, they struggle to provide the necessary surface texture when bonding with enamel. Thus, researchers have concluded that universal adhesives are most effective when using a total-etch technique with phosphoric acid.² Additionally, most single-bottle systems (both total-etch or self-etch have been reported to have lower clinical success than two-bottle systems that possess a separate hydrophobic bonding agent.³

This shouldn’t discourage clinicians from utilizing universal adhesives, however.

“Generally, I’m in support of universals-I’ve used Scotchbond Universal in my practice for the past three years with good results and there are a lot of other great products on the market—so there’s definitely a time and a place for them,” says Dr. Lineberry.

But there’s also a place for other generations of bonding agents.

“I don’t think I’d get rid of previous generations because some of these are tried and true,” Dr. Lineberry says. “They have a proven track record of how well they work. I’ve got patients that have composites that were placed with an older generation composite or bonding agent that are 15, 18, 20 years old, and still doing well. So, as the old saying goes, newer is not always better. We’re seeing good, promising results with the universals, but it’s not like we have a lot of history with them.”

Dr. Goodchild agrees, and also adds that the efficacy of a product varies from practitioner to practitioner-and there’s no one-size-fits-everyone product.

“When considering which system is most effective, it’s definitely time and place,” Dr. Goodchild says. “But I also feel like dentists are creatures of habit and subscribe to the ‘what works best in my hands’ argument. So, people will say, ‘Well, I’ve been using this for 5 or 10 or 20 years, so I know it’s good.’ Well, it doesn’t mean it’s good, it just means it’s worked for you-it could work differently in someone else’s hands.”

Avoiding universal complications

It may be easy to just reach for the universal adhesive when doing a procedure-after all, they’re easy to use, speed up procedure time and get you on to your next patient quicker. But because they are so simple, it can be easier to make errors.

“It’s definitely easier to get caught on autopilot with universals,” Dr. Lineberry says. “They simplify techniques, so you can become complacent about some of these things for sure.”

It’s also paramount to remember that not every universal is the same. There are many different formulations of universal adhesives-some still recommend using a dedicated primer or separate activator, for example—so it’s important to know how the product you are using functions.

“I don’t see any major significant clinical drawbacks with universals,” Dr. Lineberry says. “The key is to just know your product and what works. For instance, I’ve found that the product I prefer doesn’t bond well with all dual-cure buildup and core materials. So, you need to know that; you need to know that you need to mix it with a dual-cure agent or activator. If you don’t, obviously it’s not going to bond well. So, that’s one important part. You need to know those things because sometimes people just assume it’s a universal bond so it just sticks to everything, but that’s not always the case.”

Not only is it important to know what works and what doesn’t, you need to know how to implement it properly. Reading the manufacturers’ specific guidelines for a particular product can mean the difference between bond success and the patient being back in your chair in short order.

“I always fall back on following directions,” Dr. Goodchild says. “There are a lot of smart chemists working on this technology, and to think that we then, as users, can know better than the chemists who designed the product-well, we really need to follow directions to get the best outcome.”

When it comes to the bottom line, universal adhesives have shown great results, but may not be right for every situation. However, if instructions are followed, indications understood and proper implementation completed, they can provide universally successful results.

References

1. De Goes MF, Shinohara MS, Freitas MS. Performance of a new one-step multi-mode adhesive on etched vs non-etched enamel on bond strength and interfacial morphology. J Adhes Dent. 2014;16:243–250.
2. Lawson NC, Robles A, Fu CC, Lin CP, Sawlani K, Burgess JO. Two-year clinical trial of a universal adhesive in total-etch and self-etch mode in non-carious cervical lesions. J Dent. 2015;43:1229–1234.
3. Peumans M, De Munck J, Mine A, Van Meerbeek B. Clinical effectiveness of contemporary adhesives for the restoration of non-carious cervical lesions. A systematic review. Dent Mater. 2014;30:1089–1103.