Milford, Delaware, August 1, 2017 – We spoke with Huaibing Liu, Ph.D., a senior principal scientist at Dentsply Sirona, to learn about the genesis of Prime&Bond elect universal dental adhesive and the chemical properties that create a stronger restoration and a better procedure for doctor and patient alike.
Tell us a little about your background, Dr. Liu. How did you come to be involved with Dentsply Sirona and Prime&Bond elect?
I studied chemistry and materials science, earning my B.S. and M.S. in chemistry at Peking University and my Ph.D. at the University of Rhode Island. I spent a few years at Triton Systems, but soon found the perfect fit for my research interests at Dentsply Sirona, and I’ve been here since 2001.
I was involved with optimizing the PENTA manufacturing process, and I’m proud to say that PENTA has now been proven in clinical use for more than 30 years, including Prime&Bond NT™. Since then, we’ve continuously worked to develop improved options for dentists. Prime&Bond elect is one result of that effort.
What is the thinking behind Prime&Bond elect? What does it bring the practitioner’s armamentarium?
About six years ago, a new category of adhesives were developed and marketed as “universals,” claiming to work with any substrate, in both direct and indirect restorations, using self-etch, selective-etch or total-etch techniques. In other words, one size fits all.
As we know, one size rarely does fit all. For example, the first universal adhesives on the market claimed to work as a primer for glass ceramics without the need for a silane coupling agent. We knew that was scientifically unfounded, and the claim has since been refuted in many publications. That’s why we continue to recommend using Calibra® Silane Coupling Agent when bonding glass ceramics.
Nevertheless, the desire for a simple, universal adhesive had been awakened in the market, and we knew we could design a product that came a lot closer to that ideal. We also knew we could deliver bond strength equivalent to any single-purpose adhesive, using any etching technique and any substrate.
And we wanted to go beyond the bond by designing a product that handles better and works better, eliminating uncertainty about the crucial bonding step and the longevity of the restoration.
What do you mean by “handles better and works better?” What does Prime&Bond elect do that other universal adhesives can’t?
Prime&Bond elect has extremely low film thickness compared to other universal adhesives. That’s important in a Class II restoration because a thicker adhesive can tend to pool in the corners of the proximal box. On a radiograph, that pooling can easily be mistaken for a void or secondary decay, possibly leading to unnecessary removal of the restoration.
A thicker adhesive can also impede the fitting of an indirect restoration, especially with the growth in esthetic restorations and today’s extremely accurate milling technology. The low film thickness of Prime&Bond elect helps preserve the geometry of the tooth preparation to allow passive seating for an accurate crown fit.
How did you achieve low film thickness?
It’s really a function of viscosity and spreadability. When you have a product with low viscosity that spreads evenly across the prepared tooth surface, without forming pools, that’s the definition of low film thickness. Those characteristics are the result of a well-balanced formulation incorporating PENTA chemistry and a unique photoinitiating system in an acetone solvent.
Acetone? Other universal adhesives use ethanol as a solvent, right?
That’s right. Their chemistry requires the use of ethanol, which is significantly less effective than acetone in facilitating the penetration of adhesive resins into dentin tubules and demineralized dentin. Ethanol is also slow to evaporate, and difficulties with that step can result in an uneven, overly thick adhesive layer. Also, unlike acetone, ethanol can significantly reduce the effectiveness of the photosensitive dye camphor quinone. To compensate, higher levels of camphor quinone are added, resulting in a more noticeable yellow coloring that can sometimes compromise the esthetic outcome of the restoration.
Our PENTA chemistry allows the use of acetone, which chases water very effectively and evaporates readily. As long as the preparation isn’t totally dry or exceedingly moist, you can expect to get even spreading, effective tubule penetration and an exceedingly thin adhesive layer that allows for a reliable, well-fitting restoration with no surprises.
Another benefit of that tight bond with the dentin tubules is practically no occurrence of post-operative sensitivity. And a comfortable patient is a happy patient.
PENTA chemistry seems to be the key to all of this. Can you tell us exactly what it is?
You’re right: PENTA is of the utmost importance. It’s an extremely effective hydrophilic cross-linker designed to ensure a very strong, reliable bond to tooth substrates, both immediately and over the long term. It’s proprietary to Dentsply Sirona. We manufacture it in-house, and we continually improve it.
PENTA chemistry works by ensuring mechanical homogeneity in the bond layer. It’s functionally very stable because it incorporates five reactive groups in one molecule. Think of it this way: The MDP or methacryloyloxydecyl dihydrogen phosphate monomer used in other adhesives is prone to hydrolytic degradation in such a way that when one linkage breaks, the molecule splits in half so that 50 percent of the molecule is not chemically incorporated in the network structure.
That’s a bit over my head. Can you help me understand?
Sure. Basically, all resins inevitably degrade to some degree. But with PENTA chemistry, it’s a non-issue because there are five polymerizable groups in one molecule. In other words, the molecule can form bonds in five different ways. That makes it very stable. As an analogy, think about how much stronger your grip is using all five fingers as opposed to just one. An MDP monomer only has one polymerizable group. But with PENTA, the chance of all five polymerizable groups detaching from the polymer backbone is nearly zero.
Five is stronger than one — that makes sense. You said that you’re continuously working to improve PENTA. What’s the next challenge you want to solve?
A universal adhesive is a complicated mixture that includes structural resins, acidic monomers, organic solvent and water, all ideally balanced to bond with different substrates that have conflicting requirements. We’re always working to make our products more robust and reliable.
But beyond that, what sets Dentsply Sirona apart is our commitment to understanding what dentists truly need for better, more efficient procedures and a more profitable practice. Instead of asking dentists to adapt their needs to fit our product, we designed Prime&Bond elect to fit their needs.
While I can’t discuss specifics, I think the next innovations you’ll be seeing will do even more to help simplify procedures, lower overall costs and complement each dentist’s preferred techniques to deliver optimum outcomes.
We’ll look forward to that. Thanks for speaking with us today, Dr. Liu.
Thank you, it was my pleasure.
