Dr. Jeff Brucia shares with Dr. Jeff Dalin thoughts on the advantages and disadvantages of the different generations of bonding agents available to dentists today, and discusses the pros and cons of the new self-etching cements that are on the market.
Dr. Dalin: This is an interview I have been looking forward to doing, Jeff. It is on a subject that certainly needs some clarification, and I think you are just the person to help clear up a lot of confusion. Every year, we “wet-gloved” dentists are getting bombarded with new bonding agents. I think we now are up to the seventh-generation bonding agent. Can you help define these different generations of bonding agents?
Dr. Brucia: I agree with you. I easily can understand the frustration that most dentists are feeling. Let me take a moment to review the different bonding systems that are available. I will skip the first three generations of bonding agents since they are not commonly used anymore.
We will start with fourth-generation bonding agents. They are commonly referred to as etch-and-rinse, multiple-bottle systems. The placement and rinse of a 32 to 37 percent phosphoric acid gel is followed by separate primer and adhesive placement steps. Excellent examples of this category would include OptiBond FL, PermaQuik, All Bond II, and Scotchbond MP+. These systems have a long history of success. The drawback of these materials is their perceived difficulty of use.
The fifth-generation materials still fall in the etch-and-rinse category, but now have combined the primer and adhesive into one bottle of material. Examples of this generation are Bond 1, PQ-1, Single Bond, One Step Plus, Excite, Prime and Bond NT, and OptiBond Solo +. These systems have brought with them a reported increased incidence of sensitivity due to complex chemistry, and a smaller window of opportunity for technique errors.
The sixth generation is referred to by many as a nonrinse, self-etching multi-bottle system. They use a mild etch combined with the primer that no longer requires rinsing. The adhesive is then placed as a separate step. Examples of these include Clearfil SE, Simplicity, NanoBond, and Tyrian. These systems address the sensitivity problem. But at what cost?
The seventh generation further simplifies this by combining the self-etching primer and the adhesive into a one-application system. Some still require mixing prior to placement, like Prompt, while others are packaged in a single bottle, like I-Bond, G-Bond, Clearfil S3, and Xeon IV. When a material comes in one bottle, I would recommend turning the bottle upside down a couple of times, or in the case of a single-use material, stirring the material lightly with a microbrush. I believe these materials do separate into layers, and should be slightly mixed. But is faster really better?
It also should be mentioned that self-etching systems now are subdivided into three additional categories based on acid strength. They are mild, medium, and aggressive acid systems. It is hoped that the more aggressive systems will more closely match the etching patterns and performance of 32 to 37 percent phosphoric acid on enamel. There have been some reports of sensitivity with these systems, so time will tell.
Dr. Dalin: Do you find these new-generation products working better than the older generations?
Dr. Brucia: Absolutely not! By reviewing research and some of my own testing, I am finding inferior bond strengths and durability concerns. The new-generation products are definitely simpler to use because of the decreased number of steps and bottles. We do see less sensitivity with some of the newer materials, but at the expense of bond strength and durability. When materials of different properties are combined, the science becomes more complex and the perceived simpler application techniques become much more sensitive to small changes in the working environment and placement technique. The newer materials all have a lower pH to allow for this combined chemistry. At the very least, this can lead to under-polymerization, subsequent weaker bond strengths, and more rapid breakdown of the bond due to water absorption through the dentin-resin interface. This lower pH also has shown more incompatibility issues, especially with the delayed light-curing, dual-curing, and self-curing materials.
Dr. Dalin: What does that mean in clinical terms? I guess this means that I need to be making some important decisions. Do I want simplicity, and a low number of steps to perform? Do I want less sensitivity? Do I want the highest levels of physical properties? I guess you cannot have everything so you have to decide what is the most important.
Dr. Brucia: I believe these changes are detrimental to their efficacy in providing long-lasting bond stability. Clinically, this could mean faster marginal discoloration due to poor or no seal and could necessitate the replacement of restorations sooner than we want to see. As these weaker bonds fatigue more rapidly, I am concerned with increased incidences of recurrent caries.
Dr. Dalin: I have heard you refer to the history of bonding. I find this to be extremely interesting. Why don’t you tell our readers how you view that?
Dr. Brucia: In 1955, Michael Buonocore developed a long-lasting biologic seal when he discovered how resins bonded to well-etched enamel. We have yet to find any better or stronger seal than the bonding of resin to etched enamel. All dentin bonding seems to be temporary, no matter what system or generation you use. Some are more temporary than others. The way to get the most durable bond is by achieving a good seal onto etched enamel. By obsessing over the desire to get a faster, simpler bond to dentin, we are flying in the face of 50 years of tried-and-true results. Let me give you an example. Both of us have followed in our fathers’ footsteps by becoming second-generation dentists. How many times have you replaced an old, discolored resin restoration on a front tooth and found no decay underneath? This confirms a well-sealed, long-lasting composite. We replace these restorations strictly because of the color changes that have taken place. With our new composites and new bonding agents, we often will find our newly placed restoration popping off within the first few months. How frustrating and embarrassing is this? The previous restoration stayed on for 20 years or more. What is the difference? Dentists used to etch the enamel for a full minute, and then dry thoroughly with warm air until frosty. Dycal often was placed over the dentin so bonding to dentin was never an issue. A low-intensity light was used for a minimum of 60 seconds to cure the resin. This generated a ramp-curing effect to the restoration. Many of the newer techniques add greater stress to the newly formed bond. We underetch the enamel, are less careful of moisture control, use complex chemistry, and blast it with high-intensity, narrow-spectrum lights that may not even activate some of the initiators. Have we truly improved our results, or just become faster? It is OK to decrease the time of procedures as long as our end results do not suffer.
Dr. Dalin: So why are we continually going down this new path?
Dr. Brucia: It seems that the market is determining the products, not science. Dentists want techniques that are simpler and quicker. Sensitivity is a growing problem that is 95 percent a product of poor technique. Solutions to these problems may be introducing invisible concerns that will become more obvious over time. We all need to take a step back and focus on the limitations of these newer products, and look at indications and contraindications of each material that we consider using.
Dr. Dalin: You knew that sooner or later I was going to ask this question. What are you currently using in your practice?
Dr. Brucia: I think the fourth-generation bonding agents are still the gold standard. I am etching the enamel thoroughly, then applying a primer and bonding agent separately. I am also a big fan of glass ionomer bases or liners on deeper excavated areas of dentin and non-enamel margins. Products like OptiBond FL and PermaQuik have stood up to the test of science and time. It also would be difficult to practice without reaching for products like Fuji IX and Ketac Molar.
Dr. Dalin: What about the new self-etching cements that are on the market? Do we have to worry about the same issues with these materials?
Dr. Brucia: When considering a new resin cement system, the first question I ask is if the cements are indicated for veneer cementation. This truly tests a cement’s ability to achieve high-bond strength to etched enamel, dentin, and porcelain. If they are not, as is the case with the newer self-etching cements being introduced, then they are a compromise to what we currently have.
If bond is less important, and you want a highly rigid void filler that has no expansion, then let’s consider these newer materials. The newer self-etching cements, like Unicem and Maxcem, are rigid and have very good physical properties. If I wanted to fill the space when cementing a metal post or with a high-strength core crown placed over a well-prepared, self-retentive preparation, this might be a great choice. But for long-term adhesive potential, I do not believe this is the material of choice.
Dr. Dalin: I respect what you are telling me. Most of this opens my eyes to potential problems. I know you like to do some research in your own office. What ways have you found to improve the behavior of some of these cements?
Dr. Brucia: I have found that etching the tooth and applying a fourth-generation primer seem to improve greatly the short-term adhesive strengths of the newer self-etching cements. I believe that more research needs to be done in the area of techniques and procedures. There might be ways to improve the clinical results of the products we use if we reevaluate the manner in which we use them.
Dr. Dalin: Do you have any final thoughts for our readers that they can take away from our conversation?
Dr. Brucia: In the past few years, we have seen many new products in the field of bonding agents; however, I do not feel that these changes truly have been improvements. If you use proper technique with the fourth-generation bonding systems, you will find low rates of postoperative sensitivity, less concern with incompatibility issues, and you will achieve the most durable bond and seal that currently can be attained. Don’t be shy. Get as much education about this science as you can. We need to be informed consumers and care providers. Ask questions of lecturers who are speaking about this subject. Ask questions of your sales reps, and the people at booths in exhibit halls. Don’t blindly accept what one person tells you. Investigate multiple sources for information. Any way you look at it, you need to be knowledgeable about a subject in order to ask the right questions. You need to learn the indications and limitations of the products being used on your patients. When new products are developed, marketing and science are found on opposite sides of the debate. The bottom line stops with dentists, and what we do for our patients. Our patients trust that we are providing them with the best possible care. We will pay a price in the future if we find ourselves redoing work we recently performed. Enjoy every day that you practice dentistry. Have fun providing great care.
Jeff Brucia, DDS, is a graduate of the University of the Pacific School of Dentistry where he has held faculty positions in the crown and bridge and operative departments. He currently is an assistant professor of dental practice at the school. Dr. Brucia practices esthetic and restorative dentistry full time in San Francisco. Dr. Brucia can be contacted at (415) 435-3323.
Jeffrey B. Dalin, DDS, FACD, FAGD, FICD, practices general dentistry in St. Louis. He also is the editor of St. Louis Dentistry magazine, and spokesman and critical-issue-response-team chairman for the Greater St. Louis Dental Society. Contact him by e-mail at [email protected], by phone at (314) 567-5612, or by fax at (314) 567-9047.
