Question: Are three-step total-etch systems still the gold standard?
Gary Alex, DDS; Karl F. Leinfelder, DDS, MS; Edward Swift, Jr, DMD, MS
For me this is a rather interesting, personal, and somewhat nostalgic question. I was very fortunate to be involved, in one capacity or another, with many of the key players during the controversial total-etch “explosion” in the early 1990s that literally changed the way we practice dentistry.
First, I think it is important for readers to understand that total-etch was not an American idea. The fact is it started much earlier in Japan with Dr. Takao Fusayama who developed, taught, and published total-etch concepts and protocols in the early 1980s. It was then up to his protégée, Dr. Ray Bertolotti, to introduce these concepts to rather skeptical American dentists in the mid-1980s. The total-etch “torch” was then passed on to Dr. John Kanca who, during a 1988 American Academy of Cosmetic Dentistry meeting in St. Thomas, gave an impassioned lecture on a controversial total-etch protocol he developed that combined products from different manufacturers. Many were highly critical of both Kanca and Bertolotti and their “radical” ideas regarding total-etch. As it turned out, Kanca’s total-etch protocol would prove to work better than any other protocols of that time. It was then up to Byoung Suh, chemist and founder of BISCO, Inc (Schaumburg, IL), to develop and market the first complete adhesive system specifically designed to be used in a total-etch capacity. This product was the three-step, total-etch system called All-Bond® (later to be called All-Bond® 2). This innovative new product literally took the adhesive marketplace by storm. This success quickly led to the development of two competitive products, ScotchBond™ Multi-Purpose (later to be called ScotchBond™ Multi-Purpose Plus) from 3M ESPE (St. Paul, MN) and OptiBond® (later to be called OptiBond® FL) from Kerr Corp (Orange, CA). All three of these systems proved to be highly successful and helped pave the way for the “cosmetic revolution in dentistry” by enabling dentists for the first time to bond restorative materials predictably to both dentin and enamel substrates.
The basic protocol when using three-step, total-etch systems is the sequential placement of the three primary components (etchant, primer, bonding resin). These components are typically packaged in separate containers and applied in a sequential fashion. The etchant (typically 30% to 40% phosphoric acid) is placed first on enamel and dentin, followed by a hydrophilic primer and then a separate, relatively hydrophobic, bonding resin. Despite the profound success of these systems, many users found them to be complex and time-consuming. Indeed, some referred to them as “chemistry sets,” and attempts at simplification eventually led to the development of perhaps more user-friendly, but not necessarily better, adhesive systems.
Adhesive systems today can generally be placed into one of four categories: three-step, total-etch systems (fourth generation), two-step, total-etch systems (fifth generation), two-step, self-etch systems (sixth generation), and one-step or “all-in-one” self-etch systems (seventh generation). All of these systems, no matter into which category they fall, contain an acidic etchant of some type, a dentin primer of some type, and a bonding resin of some type. Acidic treatment of tooth tissues creates a zone of demineralization, which is subsequently (total-etch) or concurrently (self-etch) infiltrated with various bifunctional primers and resins. With the “simplified systems,” the primary components (etchant, primer, adhesive) are not applied in a sequential fashion from separate bottles (as they are with the original three-step, total-etch systems) but in various combined combinations. For example, with two-step, total-etch systems the primer and adhesive are premixed and delivered from a single bottle. With two-step, self-etch systems the etchant and primer are premixed and delivered from a single container while the “all-in-one” systems attempt to deliver all components (etchant, primer, and bonding resin) from a single container. While I personally would not use any of the seventh-generation “all-in-one” systems, there is no question that many of the two-step, total-etch and two-step, self-etch systems perform well when used properly and have outstanding clinical track records.
One of the reasons for the success of current adhesive systems is the use of hydrophilic monomers that enable them to interact with dentin, which is an inherently moist substrate. The problem is these same hydrophilic groups that facilitate initial primer/resin interaction with the tooth substrate can become a liability in the long term by encouraging water sorption and hydrolysis of the adhesive interface. The “ideal” dentin bonding agent would be one that is hydrophilic when first placed but would then somehow become completely hydrophobic after polymerization. Unfortunately, no such chemistry exists. One could argue that the next best thing would be gradation from hydrophilic to hydrophobic as one moves from the tooth surface to the restorative interface. Indeed, this is the strategy used by the original three-step, total-etch and two-step, self-etch systems: The initial placement of a hydrophilic primer, which is then overlaid by a relatively hydrophobic bonding resin. It is interesting to note that at least one manufacturer (BISCO, Inc) has gone full circle and recently introduced a new three-step, total-etch system (All-Bond® 3) that is formulated specifically to address these water-sorption issues.
Are the original three-step, total-etch systems still the gold standard in adhesive dentistry? The fact is none of the newer systems in today’s marketplace perform any better (and often perform considerably worse) than the original multiple component total-etch systems of the early 1990s if bond strength to dentin/enamel, microleakage, clinical track record, and versatility are used as the evaluation criteria. Indeed, there is sometimes a price to be paid for simplification. I think we need to be careful about sacrificing efficacy just to save 20 seconds or so when using an adhesive. In my opinion, we have many adhesive systems that are quite effective when used properly. Having said that, the original three-step, total-etch systems of years ago are still the standard by which these newer systems are judged.
The fourth-generation dentin bonding agents were first marketed nearly 20 years ago. They represent the first truly clinically successful adhesives available to the dental profession. Unfortunately, because of their somewhat complex technique, manufacturers have modified these systems by combining the primer with the adhesive. While the newer formulations (fifth generation) were less complex to use, they were accompanied by a substantial increase in postoperative sensitivity. Furthermore, they were considerably more expensive.
The severity of the postoperative sensitivity stimulated the next generation (sixth generation) of dentin bonding agents. While the presence of sensitivity was nearly eliminated, new problems arose. Specifically, it was determined that this new class of adhesives was not necessarily compatible with dual- or self-cured resins. These included both the dual-cured luting agents and the composite core materials. As it turned out, the elevated acidity associated with the adhesive formulations neutralized the presence of amine in the core and cementing agents. The problem was resolved by some manufacturers by including a small bottle of tertiary amine with the adhesive kit. By mixing one drop of the amine additive with the dentin bonding agent, a sufficient amount of amine was available to achieve setting without the use of light radiation.
In addition to the potential problem of incompatibility with dual-cured polymers, the sixth-generation dentin adhesives commonly were less effective than their predecessors in etching and bonding to enamel. Consequently, it was determined that the bonding agent should be allowed to react with the surface of enamel for a longer period of time than it did with the dentin. Still another problem associated with this generation of dentin adhesive related to an increase in hydrophilicity which, in turn, resulted in an increase in the permeability of the hybridized zone. Finally, the introduction of an “all-in-one” system (seventh generation ) was introduced for the purpose of eliminating the potential for postoperative sensitivity as well as making the application process more simple. The same problem associated with the sixth generation adhesive was retained with the seventh generation.
Are fourth-generation adhesives bonding systems the gold standard? Let me begin by stating that I do not like the concept of “generations” because I believe it causes much confusion. A more appropriate name for the “fourth-generation adhesives” is “three-step, etch-and-rinse adhesives.” As the name implies, these systems use three sequential steps for bonding resin-based materials, including an etchant that is applied and rinsed off.
For the past dozen years or so, the trend in resin bonding has been toward simplification—combining the primer and bonding agent, the conditioner and primer, or even all three components—into a single solution. But in simplifying the products, have we deviated from a recognized gold standard?
The three-step, etch-and-rinse adhesives have performed well in both laboratory and clinical testing. For example, our department recently submitted a manuscript for publication describing a clinical trial of one such adhesive that had a 12- year restoration retention rate of nearly 90%. These were restorations of noncarious cervical lesions with no mechanical retention, so a 12-year retention rate of 90% is remarkably good.
Laboratory studies of bond durability have shown that all resin bonds to dentin decline with time, but the more complex systems tend to have the least degradation. In addition, the three-step, etch-and-rinse adhesives have universal application; they can be used with both indirect and direct restorations, and with both self-cure and light-cure composites. This is not true for other categories of adhesives.
So, yes, it would be reasonable to state that the three-step, etch-and-rinse adhesives are the gold standard for resin bonding. However, I must admit a caveat to this statement. Just because a material, or group of materials, is the gold standard, I do not believe that it must be used all the time. Take, for example, a typical Class III preparation to be restored with composite. This preparation is likely to have some inherent mechanical retention and to be surrounded completely by enamel. In this situation, I believe that a simplified adhesive, such as an etch-and-rinse “one-bottle” material, would be perfectly appropriate.
About the Authors
Gary Alex, DDS
Long Island Center for Dental Esthetics and Occlusion
Huntington, New York
Huntington, New York
Karl F. Leinfelder, DDS, MS
Department of Biomaterials Clinical Research
University of North Carolina
Chapel Hill, North Carolina
University of Alabama School of Dentistry
Edward Swift, Jr, DMD, MS
Professor and ChairDepartment of Operative Dentistry
University of North Carolina School of Dentistry
Chapel Hill, North Carolina