Advances in Adhesion Add Complexity to Dental Education

Marcos A. Vargas, DDS, MS (MV): Well, it really hasn't changed a lot because I think that, in education, we try to teach the fundamentals of bonding rather than gearing the learning toward specific materials. Because the materials are going to continue to change so much as dentistry progresses, we're starting to move away from using brand names when we talk to the students about adhesives. So, I think the main focus is trying to teach them that there are going to be different types and to try to categorize them more by the chemistry than just by the brand because when the students finish, most of them are going to go to private practices with established bonding agents and protocols.

ID: With regard to adhesion and bonding techniques, what are the most important lessons that you try to drive home to your students?

MV: One important one, I think, is to always read the instructions before using a new material. Sometimes, we tend to just do things that we're familiar with without necessarily sitting down and reading the instructions. And when reading the instructions, we must also try to understand the "why" behind them. Why are they specifying to etch the dentin for 10 seconds instead of just saying to etch it or to etch it for 15 or 20 seconds? What is the fundamental science behind the instructions? So, if students can get out of dental school saying, "OK, I need to always read the instructions and understand why I am doing what I am doing," they will get the best out of their adhesives and bonding agents and provide the best for their patients.

ID: On the subject of adhesion and bonding, what are the biggest challenges that you see your students struggling with?

MV: Nowadays, I think the students understand the basics of bonding to enamel and dentin really well. Throughout their education, we drill the steps and the fundamentals into them through exercises and different learning opportunities to demonstrate their importance. I think the biggest struggle for today's dental students is avoiding confusion with all of the dental materials in the market that we're trying to bond to. To correctly follow all of those instructions requires a better understanding of the chemistry of the different materials. When do you bond, when do you lute, and when do you use a self-adhesive resin cement? There are three big categories of cements with lots of variants, so another struggle for the students is learning to understand which material is best to use in each situation. The problem, and it's a good problem to have, is that now, there are just so many combinations of cements, adhesives, and restorative materials to choose from that selecting the most appropriate combination for a specific situation can seem overwhelming at first.

ID: How did adhesion change as protocols moved away from the gold standard of 3 steps to 2- and 1-step protocols?

MV: The 4th generation of adhesives, or total-etch 3-step adhesives, brought us the first predictable and reliable adhesion. The three steps were to apply a phosphoric acid etchant and rinse it off, apply a primer and dry it, and then apply the adhesive. A desire to simplify this process is what drove the development of the generations to come. For the first two-step adhesives, the primer was combined with the adhesive, so the practitioner would employ a total-etch technique as the first step and then place the combined primer/adhesive. These adhesives made bonding protocols more efficient but never really lived up to the expectations of many practitioners. For the next evolution of two-step adhesives, the thought was to combine the etchant and the primer instead of combining the primer and adhesive. The search for an adhesion-promoting molecule that could be etched and infiltrate the hard tissue at the same time ultimately led to the development of MDP, which is the best monomer that currently exists. These two-step adhesives were excellent for dentin bonding but not the best for developing a bond to enamel. Some would say that combining these methods offered the best of both worlds-etch enamel, use a self-etch for dentin, and then apply an adhesive. When they attempted to combine all three steps into one, it was a disaster. The decrease in pH required to increase the bond strength to enamel made these compounds very unstable. However, the phoenix that rose from these ashes was the current, less acidic 1-step universals that can be used after a selective-etch technique.

ID: Having been around for a several years, they aren't exactly new anymore, but what are your thoughts on the emergence of universal cements?

MV: I think they have a place in dentistry. However, dentists need to recognize when each is appropriate to use because they can have very different indications. It's not like one is going to accommodate all cases. With these cements, it's a different story because there's just much more involved. How much resistance and retention form does the preparation have? That's key to choosing one of the cements. And then, at the same time, what material is being cemented or bonded? So, that's a key problem for a dentist. Not from a student's point of view, but from a dentist's point of view. A lot of dentists out there have no idea when to use some of these cements, and even choosing the appropriate restorative material can be a big deal for them.

ID: What do you tell your students and what would you say to the general dentist regarding the best way to handle or approach adhesion in practice?

MV: I think everything begins with choosing the correct material. You choose a material based on a balance of function and esthetics, right? In some cases, the esthetics are more important or as important as function. When you're working in the anterior region, esthetics are very important, so you have to find a material that is very esthetic but at the same time functional. High functional demands, such as those of the posterior teeth, require materials that are very strong, and unfortunately, these materials are not necessarily very esthetic. So, everything is about finding a balance between esthetics and function. And that's how we teach them—to decide on the material first.

ID: What's an advantage that you think your graduating seniors may have over the established practicing dentist in terms of their knowledge of adhesion and bonding?

MV: They have an advantage in that many older dentists didn't learn any of this when they went to dental school. All of a sudden, the students have a leg up on the established dentists because at least they were exposed to the ever-increasing variety of materials and cements in dental school. They know that they have more options available with complex chemistries that they need to pay attention to. So, I think that's an advantage for the students nowadays. They come out with a greater knowledge base of what's out there.

ID: What do you see on the horizon for adhesion and bonding?

MV: What is on the horizon? It can be difficult to try to predict what is going to happen in dentistry. Hopefully, I think the future will be about simplification. With ongoing improvements in chemistry, the universal adhesives and cements should follow that trend, and we will finally have a material that bonds to all substrates with equal strength using an efficient protocol. That would be great to have something like that. I think we'll get there eventually.

Marcos A. Vargas
Professor
Department of Family Dentistry
The University of Iowa
College of Dentistry
Iowa City, Iowa