PPR: Why are there so many bonding agents on the market? Is there really much of a difference between them?
ML: From a practical standpoint, I think manufacturers will develop a bonding agent because they have other products that the dentist wants to buy, so they try to offer dentists a complete system.
More importantly, though, a bonding agent system must be chemically compatible with whatever is going on top of it. This is not true in light-cured, direct-only indications, but it is absolutely essential when working with a dual-cured resin cement or post-and-core material or something of that nature because the chemistry of the bonding agent will directly affect the behavior of a cement or a post-and-core material. There are known incompatibilities with dual-cured systems and some dual-cure adhesives. So, if a company is selling a resin cement, they really need to sell an adhesive that works with that cement. That is why I think there is a lot of duplication for indirect applications.
PPR: Are there situations that are better suited to the total-etch systems?
ML: I think that if you talk to people who do adhesive research, they would say that all situations are better suited to total etch over self etch. Because the long-term performance of the best total-etch systems is generally better than that of the best self-etch systems. The shelf life, the long-term enamel and dentin bonding, and the stability of the bonding have been proven with total-etch systems and have yet to be completely proven with self-etch ones.
These qualities are very product specific. As a category, there are some pretty good self-etching systems and some pretty bad ones. In my opinion, there is a reason to use total etch over self etch every time you use a bonding agent. I say that very strongly because the laboratory and, in some cases, the clinical performance of self-etching systems, particularly with respect to enamel bonding is lower or less reliable than with a total-etch system.1,2
However, a total-etch system, in the hands of some dentists, requires more care and attention to detail with respect to whether sensitivity is going to be generated in the final restoration. And that seems to be something that self-etching systems do a little bit better. But used appropriately, total-etch systems will work better than self-etch systems and that’s bold statement, but the clinical evidence and the worldwide literature would support that statement.1-4
PPR: Are there any situations that are better suited to the self-etch systems?
ML: There is one instance when self-etching systems may make more sense. That would be if you are doing an indirect procedure that has very little if any enamel, and I’m thinking primarily of a crown preparation, and you are going to use an adhesive cementing technique to cement an all-ceramic crown. In that case, there are a couple of self-etching adhesives and cement systems that may make that application better than putting acid on the tooth, opening up all the tubules and having to go through the process of making sure you re-infiltrate the dentin. In a situation like that you’re not relying on enamel very much for a seal.
The problem with most self-etching systems is that most, if not all of them, have a lower potential to bond to enamel than total-etch systems.5
It’s a very controversial situation. The self-etching systems initially were marketed to reduce post-operative sensitivity, but if you use a total-etch system appropriately, and you follow the directions, you won’t get sensitivity either.
PPR: But aren’t the self-etching systems less technique sensitive?
ML: Not really. When you use them clinically, [you have to pay attention to some things during] application and use. [These details] are different than the things you have to pay attention to with the total-etch systems, but the self-etch have just as many idiosyncrasies. For example, you have to have cut or instrument the enamel. So, if you are doing a direct composite in an anterior tooth—a diastema closure for instance—you have to prepare the enamel. You don’t have to do that with a total-etch system.
The application time for self-etch systems is at least as long as it is for total-etch systems. The drying of the adhesive film when it’s on the tooth is much more critical because these systems have water in them so drying these products is trickier and requires more care than the total-etch products.6
Depending on the product, self-etch systems can be much less stable than the total-etch systems at room temperature. Because self-etch systems contain acid monomers in water, hydrolysis can occur quickly with some of them.
The notion of technique sensitivity for total-etch agents primarily centers around putting the acid on, keeping the dentin moist, and infiltrating to dry the solvents off. You trade those things for a different set of issues [when you switch to a self-etch agent].7-9 As you look at the whole scheme objectively, you still have to be as careful with self-etch as you are with total-etch products but with different steps. With both systems, you have to be attentive to details or the performance will [suffer]. The performance [suffering] for self etching may not be post-operative sensitivity; it may be marginal staining or restoration retention.
I do a lot of laboratory and clinical research on bonding systems. The self-etch systems behave differently on enamel than total-etch systems do. Does staining in restorations mean that there is a breakdown of self-etch systems that signifies other deficiencies compared to total-etch systems—that the bond is breaking down inside the restoration? I don’t know. I don’t know that anyone can answer that question.
PPR: Do the single-bottle varieties offer benefits over the other systems? Are there any drawbacks to the single-bottle systems?
ML: All the self-etching systems to some degree have the same drawbacks—their long-term stability in the bottle, the stability of the bond in the tooth, the issues of maximizing enamel adhesion. The single-bottle self-etching systems are less water stable, because you have water, acid monomers, and everything else in one bottle so they’re even fussier.10,11 For example, you can put a single-bottle agent out in a dappen dish and watch it over the course of the 30-45 seconds. It looks like a uniform solution when you put it out, but if it undergoes separation, you see the droplets separating out. So, if the assistant dispenses the material two minutes before the doctor’s going to use it, not only does the solvent flash off but the material undergoes phase separation. And once it undergoes separation, it won’t work.
PPR: Dentists have told us that bond strength values are an important factor when they are choosing a product, but we have heard that values from lab tests can vary according to test methods or placement techniques and that clinical studies can take so long to complete and publish that they are often outdated by the time the dentist gets them. Any advice on how to choose a good bonding agent?
ML: I would say, don’t buy anything in its first year or two [on the market]; wait until the clinical data come out.
The screening [before a product enters the market] for dental bonding systems is not very in-depth. Some laboratories use bovine teeth, which does not exactly correlate to human dentin,12 but they use bovine teeth because it’s difficult to get human teeth for research. In some places, Institutional Review Boards may have restrictions for using biological matter taken from patients in laboratory tests. In some cases, researchers use bovine teeth because of infection control issues.
Part of the rationale in using bovine teeth is that with total-etch systems the bond strength to both enamel and dentin are different than you would find with human teeth, but if you’ve done enough in-vitro work on bovine teeth. If you have a system that has been in some good clinical studies for 15 years—and we’ve got data from that long ago on some systems—you could correlate generally what you get in the laboratory with the bovine data. Dr. Bart van Meerbeek has done a lot of these studies.13-15 You can use bovine teeth if you’ve got a base of data for older systems that have known clinical performance data—you can make some deductions about how the two correlate.
When self-etching systems were developed, a lot of those correlations broke down, though, and what we saw in the laboratory didn’t translate to the clinical studies as it did with the total-etch systems. If you look at total-etch systems, they perform better clinically than you might predict from their laboratory performance. Self-etching systems are the opposite. They actually perform worse in some cases than you might have predicted from the in-vitro data. It’s just my observation—it’s not something that has been focused on in the literature.
Some laboratories use human enamel, but they use different test methods (microtensile or shear methods) that yield different values. When you try to correlate laboratory bond values to clinical evidence in the literature going back 15 years on the systems we have experience with now, you can get a very general idea about what a material is going to do clinically. The reality is that with bond testing you just are not able discriminate between products.
Unfortunately, the latest and greatest product, isn’t the one you should be snapping up. I tell dentists, when a sales representative comes into your office, ask to see the clinical studies. How long has the clinical evidence been collected? You can get anything to hold for six months, but you want to know how effective it is in two or three years.
One of the problems dentists face is that [advertisements] can be deceptive. They show a bar chart that is scaled to look like there’s a difference, when really, there is no difference. Or they take data from different studies done in different ways and combine them into one graph. Or they compare bovine versus human tissue. There are so many things that as a scientist you know to look for, and you know the impact of, that average dentist doesn’t know to watch for.16 So [advertisements] can give dentists a very imperfect view of a product’s actual performance.
PPR: Is there anything you’d like to comment on that we haven’t covered?
ML: I think dentists should reconsider how they think about bonding agent systems. Bart van Meerbeek and Klaus Peter Ernst have published what I think is a more logical classification system for bonding agent systems.17 They suggest that you refer to Etch-and-Rinse systems rather than Total Etch because the self-etch systems are totally etching the too, you just don’t rinse them off. So, there are Etch-and-Rinse systems and there are Self-Etch systems. Then, within the Etch-and-Rinse category, you have three-step systems (acid etchant, primer, and adhesive like Optibond SL and Scotchbond Multi Purpose) and two-step systems that use an etchant plus a single bottle that combines the primer and adhesive—that would be PrimeBond NT, Excite, Single Bond, and OptiBond Solo. Then, on the Self-Etching side, you have Self-Etching Two-Step systems that use a primer and an adhesive like ClearFil SE Bond, Self-Etching One-Step Mix, where you mix two solutions together and apply one solution to the tooth like Adper Prompt L-Pop. Finally, you’ve got Self-Etching No Mix, or single bottle, systems like iBond or Xeno IV (Table).
The whole generational classification system implies superiority, but that’s just a fabrication because if you look at the data the more recent generations don’t necessarily work as well as the earlier generations. It’s misleading—it’s not a descriptive term.
Dentists try to oversimplify this. The point I make to dentists is that the mechanism for all those five categories is very similar, but how you get to the end result is very different. The mechanism is that we take out mineral from the tooth—both enamel and dentin—and we replace the mineral with the resins or organic monomers that are in the adhesives. That’s the fundamental mechanism of adhesion. What happens on those surfaces is different and more complex. Each and every time you bond a restoration, you make a new composition of matter. You create an interface that’s a mixture of mineral (in the case of dentin), some collagen, and the adhesive materials themselves. So, you have to pay attention to the details—it’s not just painting something on … it’s manipulating and managing the surface and the material to create this microscopic interface.18-20
1. Perdigao J, Gomes G, Duarte S Jr, Lopes MM. Enamel bond strengths of pairs of adhesives from the same manufacturer. Oper Dent 2005;30(4):492-9.
2. Can Say E, Nakajima M, Senawongse P, Soyman M, Ozer F, Ogata M, Tagami J. Microtensile bond strength of a filled vs unfilled adhesive to dentin using self-etch and total-etch technique. J Dent 2006;34(4):283-91.
3. De Munck J, Shirai K, Yoshida Y, Inoue S, Van Landuyt K, Lambrechts P, Suzuki K, Shintani H, Van Meerbeek B. Effect of water storage on the bonding effectiveness of 6 adhesives to Class I cavity dentin. Oper Dent 2006;31(4):456-65.
4. Chang J, Platt JA, Yi K, Cochran MA. Quantitative comparison of the water permeable zone among four types of dental adhesives used with a dual-cured composite. Oper Dent 2006;31(3):346-53.
5. Brackett WW, Ito S, Nishitani Y, Haisch LD, Pashley DH. The microtensile bond strength of self-etching adhesives to ground enamel. Oper Dent 2006;31(3):332-7. Erratum in: Oper Dent 2006;31(4):520.
6. Chiba Y, Yamaguchi K, Miyazaki M, Tsubota K, Takamizawa T, Moore BK. Effect of air-drying time of single-application self-etch adhesives on dentin bond strength. Oper Dent 2006;31(2):233-9.
7. Fabre HS, Fabre S, Cefaly DF, Carrilho MR, Garcia FC, Wang L. Water sorption and solubility of dentin bonding agents light-cured with different light sources. J Dent 2006.
8. Sattabanasuk V, Shimada Y, Tagami J. Effects of saliva contamination on dentin bond strength using all-in-one adhesives. J Adhes Dent 2006;8(5):311-8.
9. Chiba Y, Rikuta A, Yasuda G, Yamamoto A, Takamizawa T, Kurokawa H, Ando S, Miyazaki M. Influence of moisture conditions on dentin bond strength of single-step self-etch adhesive systems. J Oral Sci 2006;48(3):131-7.
10. Van Meerbeek B, Van Landuyt K, De Munck J, Hashimoto M, Peumans M, Lambrechts P, Yoshida Y, Inoue S, Suzuki K. Technique-sensitivity of contemporary adhesives. Dent Mater J 2005;24(1):1-13.
11. Van Landuyt KL, De Munck J, Snauwaert J, Coutinho E, Poitevin A, Yoshida Y, Inoue S, Peumans M, Suzuki K, Lambrechts P, Van Meerbeek B. Monomer-solvent phase separation in one-step self-etch adhesives. J Dent Res 2005;84(2):183-8.
12. Pashley DH. In vitro simulations of in vivo bonding conditions. Am J Dent 1991;4(5):237-40.
Document posted 2007 © 2007 American Dental Association ADA Professional Product Review 9 Bonding Agent Systems: Adhesives Expert Interview Volume 2: Issue 1 Winter 2007 (Online) www.ada.org/goto/ppr
13. De Munck J, Van Landuyt K, Peumans M, Poitevin A, Lambrechts P, Braem M, Van Meerbeek B. A critical review of the durability of adhesion to tooth tissue: methods and results. J Dent Res 2005;84(2):118-32.
14. Peumans M, Kanumilli P, De Munck J, Van Landuyt K, Lambrechts P, Van Meerbeek B. Clinical effectiveness of contemporary adhesives: a systematic review of current clinical trials. Dent Mater 2005;21(9):864-81
15. Van Meerbeek B, Perdigao J, Lambrechts P, Vanherle G. The clinical performance of adhesives. J Dent 1998;26(1):1-20.
16. Eckert GJ, Platt JA. A statistical evaluation of microtensile bond strength methodology for dental adhesives. Dent Mater 2006.
17. Van Meerbeek B, Vargas MA, Inoue S, et al. Adhesives and cements to promote preservation dentistry. Operative Dent 2001; Supplement 6:119-43.
18. Nishitani Y, Yoshiyama M, Wadgaonkar B, Breschi L, Mannello F, Mazzoni A, Carvalho RM, Tjaderhane L, Tay FR, Pashley DH. Activation of gelatinolytic/collagenolytic activity in dentin by self-etching adhesives. Eur J Oral Sci 2006;114(2):160-6.
19. Toledano M, Osorio R, Albaladejo A, Aguilera FS, Osorio E. Differential effect of in vitro degradation on resin-dentin bonds produced by self-etch versus total-etch adhesives. J Biomed Mater Res A 2006;77(1):128-35.
20. Koyuturk AE, Sengun A, Ozer F, Sener Y, Gokalp A. Shear bond strengths of self-etching adhesives to caries-affected dentin on the gingival wall. Dent Mater J 2006;25(1):59-65.
21. Ernst CP. Positioning self-etching adhesives: versus or in addition to phosphoric acid etching? J Esthet Restor Dent 2004;16(1):57-69.
Document posted 2007 © 2007 American Dental Association ADA Professional Product Review 10 Bonding Agent Systems: Adhesives Expert Interview Volume 2: Issue 1 Winter 2007 (Online) www.ada.org/goto/ppr
Table. Suggested Classification for Bonding Agents.*