Bonding 101: Everything you need to know to have satisfied patients

September 1, 2015

“Dentists today rely on bonding 90 percent of the time,” said Dr. Sam Simos, DDS, a cosmetic dentist at All-Star Smiles is Bolingbrook, Ill. “Everything we do requires us to have knowledge or do at least some kind of bonding on pretty much everything we do.”

Bonding resin to tooth structure is still confusing, but, with these tips, it doesn’t have to be.

Bonding is at the heart of a majority of dental work and, as such, is a ubiquitous technology and procedure. it means different things in different applications, but it is also an ever-changing thing.

There are two types of bonding involved in dental work: Direct and indirect.

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Direct and indirect bonding

Direct dental bonding is a procedure where tooth-colored composite restorations are placed on a single tooth or multiple teeth. In this case, the procedure is performed to restore function or shape or enhance the shade of the affected teeth. Once the composite is placed, shaped and smoothed on the tooth or teeth, it is cured.

Direct dental bonding is most common for anterior teeth because it tends to be easier and the esthetic results are excellent.

"Dentists tend to be good at the direct bonding,” Dr. Simos said. “The big gap is with the adhesives and the indirect substrates.”

Indirect dental bonding is more involved and usually requires the work of a dental laboratory. In this application, the restorations are started by the dentists but manufactured by a dental laboratory. An impression or mold of the patient’s affected teeth is taken. Once the mold has been made, it is sent to a dental laboratory, and then a lab technician makes the dental bonding or restoration “indirectly.” The restoration is returned to the dentist who places it in the patient’s mouth.

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The doctor can perform indirect bonding via analog methods, which involves taking an impression of the teeth using polyvinyl siloxane and then sending the mold to the lab. Other doctors do it all digitally by using an intraoral scanner and then sending it to the lab via the Internet. The only time anything physical is involved is when the restoration in shipped back to the doctor.

Indirect bonding is generally recommended for large restorations because it minimizes the shrinkage that naturally occurs when the material cures. Indirect bonding is most common in the posterior teeth. If the dentist is equipped with a dental mill, he or she can do the work in-house, but that is only a small percent of doctors. Typically, the restoration is made at a lab and placed by the doctor.

The biggest knowledge gap, Dr. Simos said, is in the world of indirect bonding.

“The types of crowns we can manufacture now in lithium disilicate or zirconia crowns, which are a kind of porcelain crown, are totally treated differently,” he noted. “Those have to be treated in a certain way before you can actually bond them. And then the rooting cements are certainly so much different than they were even three years ago.”

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Adhesives

A big area where bonding has changed involves the adhesives used to affix restorations in place.

“Not only have our composites changed, and we are now into nanoparticle composites, bulk-fill composites and composites that really wear just like teeth, but also our bonding agents have changed so much,” Dr. Simos said. “We’ve gone from three-component systems of bonding agents to one-bottle systems where everything is all in there. Literally, the paradigm in bonding both direct and indirect has changed dramatically in the last three to five years.”

It’s knowledge about adhesives that Dr. Simos suggested doctors tend to lack.

“Direct bonding has always been a very commonplace thing in dental offices,” Dr. Simos observed. “They know how to bond direct restoratives. Things lacking in the indirect arena are not necessarily the composites but the knowledge of the adhesives. That’s a huge learning gap that is out there. They just don’t know how to use the newer adhesives. They’re still using third-generation adhesives, which work, but they’re so much better in the seventh generation. There’s a big learning gap with a lot of different doctors.”

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Bonding improvements

Doctors who aren’t keeping up on the current generation of adhesives might find themselves slipping even further behind as products continue evolving.

The science of bonding isn’t a simple issue of putting some glue on a tooth and then slapping a restoration on top of it. To create the best adhesives, manufacturers must know how the body reacts to the materials and work within those parameters.

"We’ve been trying, in our current restorative process, to put a hydrophobic material into a hydrophilic tooth,” said Dr. John Comisi,DDS, president and CEO of Dental Care With a Difference in Ithica, N.Y. “The body has a reaction to what we’re doing to it. Teeth aren’t stone; they’re a living, breathing structure, and for every action, there’s a reaction.”

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There is some thought that the current approach to bonding agents is prone to failure.

"That’s why it’s interesting to talk about bonding agents right now,” Dr. Comisi noted. “Some research articles released over the last several months have challenged our use of bonding agents and the concern with the number of ultimate catastrophic failures occurring. It is being shown that dental structures are essentially rejecting the bonding agent over the course of time and break it down via an enzymatic reaction.

“Some of those enzymes, called MMPs, will start to degrade the dentin/hybrid layer interface and create bond failure. Since the dentin has a high concentration of water, we never really are able to get complete envelopment of the dentin in the formation of the hybrid layer. This enables water to invade the unsealed dentin, enabling the release of the various enzymes from the dentin structure, which starts the process of enzyme break down of the hybrid layer. So even if our initial bond strengths are fabulous, over time, the bond will degrade due to this enzymatic breakdown. If there is no ingredient present to stop the MMP degradation, the bond is doomed to fail.”

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Manufacturers need to respond with products made to combat that reaction.

"Some products, like Shofu’s BeautiBond, contain carboxylic acid, which is an MMP inhibitor,” Dr. Comisi said. “It also has great initial bond strength as well, and it’s a very thin film thickness (5 µm). It’s very easy to use so that’s why I call for it a lot when I’m doing a conventional composite restoration. I know even if the body tries to break it down eventually, the process will stop and extend the lifespan of that bonded restoration.”

With any seventh-generation bonding agent, Dr. Comisi advised etching for optimal results.

“I would also suggest the enamel portions of the preparation be etched selectively to help enhance the enamel bond with all seventh-generation bonding agents, including BeautiBond,” Dr. Comisi suggested. “For me, it is the basic ‘belt and suspenders’ approach that has helped my conventional restorative process become more predictable and reliable.”

While bonding agents seem like long-term solutions, they are not.

“Bonding agents are great intermediates, but there is question about the long term,” Dr Comisi said. “The literature is indicating an average life span of 5.7 years. That’s a great concern.”

Paradigm shift

The science behind bonding may even change to the point where it is a completely different thing than it is today. However, that change may not come soon nor be easy.

"The unfortunate reality is we’re stuck because this is what most of the industry wants to do, at least in the United States,” Dr. Comisi said. “Other companies are looking at this differently. Pulpdent introduces ACTIVA BioACTIVE, a restorative material that can form apatite because it can release calcium and phosphate ions from its hydrophillic resin matrix. Other examples of apatite forming products are Septodont’s Biodentine, and Doxa’s Ceramir. BISCO’s Theracal LC can withstand biting and chewing but has calcium phosphate that can release. We’ve been barking up the wrong tree and looking at fluoride as our basic benefit, but for apatite, you need calcium and phosphate so that’s why I keep coming back to the need for what I call reservoir restorative material. These are ways of closing the gap and enabling happiness in the tooth structure.”

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It might take time, but, eventually, the industry will respond in a way that embraces this transformation, Dr. Comisi said.

“In 10 years, we’ll look back on this and realize the necessity of this change and how moving from hybridization ultimately is a good thing, and how silly we were to think that resin bonding was our savior when in actuality it was the problem,” he observed.

Education

Like most procedures learned in dental school, bonding has continually evolved, and how you performed the procedure last year is different than it was five years before that and even five years before that.

“I went to school 24 years ago, and absolutely nothing I learned in dental school is the same as it is today,” Dr. Simos said. “The technology has changed. The materials have changed. The chemistry has really changed, and we have to understand that as dentists to be successful.”

Where does one go to keep up with new products and techniques?

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“Manufacturers really don’t give you the education,” Dr. Simos observed. “You just have to go out and seek it out, unfortunately. There is no one path of doing it. Dental school is not really the be-all and end-all of it because materials are changing so fast.”

Dr. Simos is in the unique position of teaching bonding techniques, so he is afforded rare opportunities to learn more and keep up with industry changes.

“I teach bonding so I have access to the manufacturers and what they’re bringing out,” Dr. Simos said. “I do a lot of reading of studies and articles to see what works and what doesn’t work. I also have a group of dentists I interact with that really are on the cutting edge of technology and materials. I’m a little different than most because my depth is a little bit different. I took a lot of postgraduate courses after dental school, and I’m kind of a continuing education junkie.”

Doctors must change with the times in order to be successful not only in bonding but any dental technology.

“Can we bond the way that we used to? Yes,” Dr. Simos said. “Should we? No. It’s just a totally different playing field.”

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