Tooth-colored fillings, onlays and veneers are held to your tooth by an adhesive, and so are our crowns. It’s a thin layer you’ll never see, and it does two jobs: it holds the restoration on, and it seals the edge where the restoration meets your tooth, so fluids and bacteria can’t seep in underneath.
Bonds rarely fail all at once. More often, the seal at the edge breaks down gradually. That can show up as a stained line around a filling, sensitivity, or decay that starts underneath, where it’s hard to see. Which adhesive goes on your tooth, and how carefully it goes on, has a lot to do with how long that seal holds.
- The adhesive is the thin layer that holds bonded dental work in place and seals its edges. You can’t see it, but a lot of how long the work lasts depends on it.
- Adhesives don’t all perform alike. In a 2014 review of clinical trials, some types failed two to three times as often as others, and brands of the same type varied too.
- For fillings and for sealing teeth, we use Kerr OptiBond FL and Kuraray Clearfil SE Protect, multi-step systems with some of the longest track records in dental research. Crowns and onlays are bonded with Ivoclar’s matched system.
- These systems cost more and take more steps. We think the long-term research, and the results we see, make that worth it.
What an adhesive actually does
Teeth aren’t easy to glue. Enamel, the hard outer layer, is mostly mineral, and it bonds very well once it’s been etched. Dentin, the layer underneath, is a different material: it’s moist, full of microscopic fluid-filled tubes, and has far more organic material than enamel. Bonding reliably to dentin is the hard part, and it’s where adhesives tend to differ most.
An adhesive soaks into the microscopic texture of a prepared tooth and then hardens in place, locking into the tooth on one side and the filling or cement on the other. Some adhesives also bond chemically to the calcium in the tooth. Done well, the tooth is sealed. Done poorly, a microscopic gap is left at the edge.
Bond strength isn’t the whole story
Adhesive makers often advertise bond strength numbers measured in a lab. Those numbers mean something, but a bond that’s strong on day one has to survive years of chewing, hot and cold, and constant moisture. What matters to you is durability: how well the bond and its seal hold up in a real mouth, over years.
Researchers measure that by bonding fillings into the shallow notches that wear into teeth near the gumline. Those notches have little shape to hold a filling in, so the adhesive does nearly all the work. If the bond fails, the filling comes out. That makes these long-term studies one of the clearest tests of an adhesive.
Not all adhesives are equal
There are a few broad ways to bond to a tooth:
- Three-step etch-and-rinse. An acid gel prepares the tooth and is rinsed off, then a primer goes on, then a separate adhesive. The most steps, and the longest history.
- Two-step self-etch. An acidic primer prepares and primes the tooth at the same time, with no rinsing, and then a separate adhesive goes on top.
- Simplified systems. Steps are combined, down to a single bottle that does everything in one coat. They’re faster and simpler.
A 2014 review pooled clinical trials of fillings placed in those gumline notches and compared how many failed each year. The best performers, mild two-step self-etch and three-step etch-and-rinse adhesives, averaged about 2.5% and 3% a year. Two other types averaged about 6% and 8%. Just as important, results varied widely between brands of the same type, and the authors advised choosing products with proven clinical performance.
What we use, and why
Kerr OptiBond FL
A three-step etch-and-rinse system: an acid gel, a primer, and a separate adhesive filled with fine glass particles. Researchers often use it as the gold-standard comparison when testing other adhesives. In one study that followed fillings for 13 years, 88% of the OptiBond FL fillings were still clinically acceptable, significantly better than the other adhesive in the study.
Kuraray Clearfil SE Protect
A two-step self-etch system built on Clearfil SE Bond, which is widely treated as the benchmark for self-etch adhesives. It adds an antibacterial ingredient in the primer and fluoride release in the adhesive. Its key ingredient, MDP, bonds chemically to the calcium in your tooth. In a randomized trial that followed Clearfil SE Bond fillings for 13 years, only two of the fillings researchers could still examine had come loose, and 86 to 93% were rated clinically successful.
Ivoclar’s bonding system
A crown or onlay has to bond in two places: to your tooth, and to the inside of the restoration. For both, we use Ivoclar’s system: a cleaning paste and a primer for the restoration, an adhesive for the tooth, and a resin cement, all designed and tested to work together. Adhesives and cements from different systems can interfere with each other, which we explain in The mouth is a hostile environment.
Two systems, layered on purpose
When we prepare a tooth for an onlay or crown, we seal the freshly cut dentin right away, before the tooth is scanned, instead of waiting until the restoration is bonded. It’s called immediate dentin sealing. A review of the research found that it appears to improve bond strength, with fewer gaps at the edges, less bacterial leakage and less sensitivity. For that seal we use both of our adhesives: Clearfil SE Protect first, then OptiBond FL on top. It’s a deliberate combination, and in our experience it works very well.
What “gold standard” does and doesn’t mean
OptiBond FL and Clearfil SE Bond are the adhesives new products are commonly measured against. That reputation comes from decades of use and some of the longest clinical follow-up of any adhesives.
It doesn’t mean every other adhesive fails. A 2021 review of randomized trials found that, head to head, other well-made brands generally held fillings in about as well, though the evidence was limited. The one exception: at five to eight years, OptiBond FL did better, based on three studies. We take that seriously. We still choose these systems because their long-term record is among the most complete, and because in our hands they’ve performed very well.
Why it costs more, and why we do it anyway
These systems cost more than simpler adhesives. They also take more steps and more time in the chair, and every step has to be done in order, for the right number of seconds, on a tooth that stays completely dry. Because nobody will ever see the adhesive, it’s an easy place to cut corners. We’d rather not.
We take the time to do each step the way the manufacturer intended, and we keep the tooth isolated with continuous suction while we bond, because a speck of saliva at the wrong moment weakens the bond. A few extra minutes and a few extra dollars on the part you’ll never see is one of the better investments in how long your dental work lasts.
Nobody will ever see the adhesive. That’s exactly why we don’t cut corners on it.
The bond is a partnership
Even a perfect bond lives in your mouth, not in our office. New decay at the edges and fracture are still the most common reasons bonded work fails. Keeping sugary and acidic drinks to mealtimes, not chewing ice or using your teeth as tools, cleaning between your teeth, and keeping your checkups all protect the bond. Our guide to the habits that decide how long bonded dental work lasts covers each one.
What to ask any dentist
Adhesive dentistry is complex, but it has become much more predictable. You don’t need to know the chemistry to ask good questions, and we encourage you to ask any dentist, including us:
- What adhesive are you using, and why?
- Is there long-term clinical research behind it?
- How will you keep the tooth dry while you bond?
- For a crown or onlay, are the adhesive and the cement from the same system?
A dentist who has thought about it will have a ready answer.
Myth vs fact
- Myth: All bonding agents are basically the same. Fact: In clinical trials, some types of adhesive failed two to three times as often as others, and brands of the same type varied too.
- Myth: A higher bond strength number means a longer-lasting filling. Fact: Lab numbers are a starting point. What counts is how the bond holds up over years in a real mouth, which is what long-term clinical trials measure.
Summary
The adhesive is the part of your dental work you’ll never see, and one of the parts that decides how long it lasts. We use multi-step systems with some of the longest track records in dental research, follow every step the way it was designed, and keep the tooth dry while we bond. They cost more and take longer. We think it’s worth it.