Bioactivity and the Stunning Progress of Dental Materials

Bioactivity and the Stunning Progress of Dental Materials. Image credit: © brankospejs - stock.adobe.com

In the early 1980s, there was a resurgence of interest in the 1960s science fiction television series Star Trek. Movies were made featuring the original cast, who continued the adventures of the crew on the Starship Enterprise.

I’m not sure which it was, but in one of those movies the crew had traveled back in time to the early 1980s, allowing the action to take place in the time period that it was actually filmed, instead of the far-flung future. One of the scenes stuck with me. The crew somehow ends up in a Los Angeles, California, hospital. They are keeping the fact that they are from the future a secret. Dr “Bones” McCoy, played by DeForest Kelley, sees an older female patient in the hospital. She is weak and dying from kidney failure. He looks around and, making sure no one can see, gives her a pill. Later in the movie, we see this lady who is now highly energetic and all smiles, proclaiming, “The doctor gave me a pill and I grew a new kidney!”

The theater burst into laughter and applause. It was a great example of how progress in health care can change things. More importantly, I felt it showed that what we think of today as state of the art can be viewed as archaic and sometimes even barbaric when viewed through the lens of the future.

Although it isn’t possible yet, I can see a similar story in dentistry at some point in the, hopefully, not too distant future. Our knowledge of stem cells and genetics one day may allow a doctor to extract tooth #19, and then, instead of placing grafting material in the socket, the assistant will hand the doctor some material in a syringe that is marked “Tooth #19.” The doctor will express the material into the socket, close it in some way that the material stays put, and in a short amount of time a new tooth #19 will grow.

That’s still a dream, but so was the idea of carrying a computer in your pocket that had access to the sum total of all human knowledge.

Progress

Since about 2010 the profession has seen incredible progress in bioactive materials that are greatly changing the treatment we render and the results we achieve. I frequently tell my patients, “Dentistry is really amazing, but I cannot make anything better than what was installed at the factory.” Sometimes we fall victim to our own success. Patients will present with a problem and think that it is a simple matter to put them back together “better than ever.” That’s a tall order. However, often we also don’t give ourselves enough credit for the amazing things we are capable of as a profession.

One of the first and most popular bioactive materials was calcium hydroxide, which was used in bases and liners. In the definition of bioactive, it worked. The material was placed into an area of a prep that was deeper and therefore closer to the pulp. In the days when it first came to market, the most common and preferred restorative material was amalgam. Being that it was metal, it had the unpleasant tendency of transferring the sensation of cold very easily. Deeper preps tend to cause sensitivity for a variety of reasons, but 2 of the most common were reducing/removing the amount of insulating tooth structure and causing pulpal inflammation from the process of removing the caries.

When you combined those 2 situations with the thermal conductivity of metal, this meant that a deeper restoration was almost guaranteed to cause postoperative sensitivity. To the rescue came calcium hydroxide. Not being metallic, it had the benefit of providing a noncold transferring layer of insulation between the metal restoration and the pulp. It also had the benefit of being antibacterial, as well as the ability to stimulate secondary dentin formation in proximity to the pulp. At the time, it was a tremendous help in restorative procedures.

Evolution

As I’ve said here many times, one of the best things about science and technology is that progress is always happening. That means that often even small bits of improvement can have some pretty profound results. So it is with calcium hydroxide.

The material was an easy product to apply. You simply mixed 2 pastes, picked up some of the material (which was a fairly high viscosity “goo”) with a placement instrument, and dabbed it onto/into the area of need. You could affect the set time a bit by adjusting the proportions of base and catalyst as well as by mixing, but the set was unpredictable. Often doctors didn’t wait for the material to set and would go straight to placing the amalgam directly over it. A setting time between 2.5 and 5.5 minutes simply was too long for most procedures.

The problem with not allowing the material to fully set was that as the highly dense amalgam was condensed on top of it, the base was thinned and displaced somewhat by the pressure. However, usually there was enough in place to achieve the desired result.

Yet despite its positive benefits, even when allowed to fully set, calcium hydroxide is hydrophilic. Between microleakage of the restorative material and fluid release from the dentinal tubules, frequently there was more than enough liquid to soften the material. This leads to a precipitous drop in compressive strength, which then leads to further problems.

Placing a solid material such as amalgam or composite over a material that is soft (or softens over time) leads to microflexure of the material as it is loaded by occlusal forces. Apical displacement of the material leads to sensitivity, marginal breakdown, and eventually failure of the restoration.

The good news is that this problem has been overcome by a new series of light-cured calcium hydroxide materials (Calcimol from VOCO Dental, TheraBase® from BISCO, Ultra-Blend™ from Ultradent, and others). These materials utilize a urethane dimethacrylate resin that allows them to photopolymerize while also greatly decreasing solubility and achieving high compressive strength. These materials are also significantly easier to use because they do not require separate mixing prior to application, yet they also provide all of the benefits doctors appreciate and expect from calcium hydroxide bases.

Next-Generation Progress

Calcium hydroxide has several benefits, and stimulating dentin formation is one of them. However, the dentin formation is reparative in nature. It basically allows the cells in the pulp to wall themselves away from insult. Dentin is formed along the border of the pulp chamber, and the pulp itself shrinks. It is sort of “painting itself into a corner” as it lays down this reparative dentin. What the next step forward in bioactivity provided was the formation of structures outside the pulp.

Next-Generation Cements

We’ve seen some amazing progress made with prosthetic cements. These materials have not only allowed the profession to help with sensitivity but also to help with marginal gaps. The profession has always battled marginal gaps when it comes to fixed prosthetics. In the very early days of fixed prosthetics, the cements were soluble and very small, and tight margins were needed to prevent washout of the cement. If the cement disappeared in that area, it left a void that then created a toehold for recurrent caries.

The advent of resin-based cements helped greatly. Basically, the cements were similar to permanent filling materials, so washout became a minimal concern. However, even gaps of 50 µm that could not be properly cleaned created the risk of plaque sitting undisturbed in that area and might then lead to recurrent caries.

There was also the problem of sensitivity. The act of preparation created cut dentin that could create pain as pressure differentials were applied across the ends of those cut dentinal tubules.

There is nothing better to replace missing tooth structure than tooth structure, and new cements came to market that helped do just that. Cements such as Doxa Dental’s Ceramir® allowed for remineralization, which leads to apatite formation on the surface of the tooth cement interface. This means that the material integrates with the tooth at the molecular level. Closing dentinal tubules with the material that is the building block of the tooth helps greatly decrease recurrent decay and postoperative sensitivity.

Other cements release chemicals that help reduce decay and sensitivity but in a different manner. BISCO’s TheraCem® releases calcium and fluoride. The smart minds at BISCO have developed a hydrophilic matrix that releases calcium hydroxide and fluoride ions as water is absorbed. This is another bioactive approach that decreases sensitivity and helps prevent recurrent decay.

Next-Generation Restoratives

The profession recently also has seen the concept of bioactivity move into direct restoratives. For a number of years, doctors have used glass ionomer restoratives in pediatric cases or for individuals who have dry mouth and/or a high caries rate. However, those materials can crumble, crack, or wear down extremely rapidly.

Pulpdent has an interesting product called Activa™ BioActive that offers the best of glass ionomers and traditional composites. It is a bioactive composite that puts the advantages of glass ionomers inside a strong resin matrix. This means that the material will chemically bond to enamel and dentin while also releasing fluoride, phosphate, and calcium. It also recharges to absorb those ions when it is exposed to them and rereleases them over time to help protect the tooth and the restoration.

One of the materials that I am really impressed with in the bioactive realm is the RE-GEN™ line from Vista Apex. RE-GEN is a group of products based on a material called Bioglass 45S5 (calcium sodium phosphosilicate). Bioglass is a truly amazing material that promotes the formation of hydroxyapatite while also neutralizing acid erosion. It is nothing short of groundbreaking that these products can grow tooth structure while at the same time stopping acid that is the reason for tooth breakdown.

One of the things about innovation is the matter of how it is applied. Often a product or an ingredient that is a total disruptor of an industry is released into the market a little bit at a time. That is definitely not the case with the RE-GEN technology. I give Vista Apex a tremendously high score for bringing their Bioglass products to the market as a completely new line of products. That allows doctors to get the benefits of RE-GEN in as many ways as possible. It’s a tremendous benefit to doctors, but more importantly, it brings the remarkable benefits of RE-GEN to patients…and that is who we are all striving to help.

The RE-GEN line includes Universal Adhesive, Self-Etch Adhesive, Flowable Composite, Bulk Fill Composite (dual cure), Dentin & Enamel Cleanser (Clean and Boost®), and Pit & Fissure Sealant. I am thrilled with the concept of using a bioactive material from start to finish in cases that require it. The RE-GEN line allows me to do just that. I can use a bioactive bonding agent, base with a bioactive flowable, and then restore with a bioactive bulk fill composite that I know will totally set because it is dual cure. This puts a shield of bioactivity throughout the restoration.

Recently, the company also announced a new RE-GEN EndoSealer. The endodontic market lately has seen a pronounced shift, thanks to advances in sealers. Utilizing BioGlass with the RE-GEN chemistry from Vista Apex is truly promising. I was asked to test the product prior to the nationwide launch, and I have had remarkable success with it. Studies have shown that a large number of endodontic failures are caused by coronal leakage between the time of obturation and final restoration. Having a bioactive material creating a seal at the canal orifice greatly decreases the chance of bacterial contamination taking place prior to the placement of the final restoration. Using the RE-GEN Endodontic Sealer and then covering the pulpal floor with RE-GEN Adhesive and RE-GEN Flowable ensures that the shield of bioactivity helps protect the filled root canal system as well.

And then we are also seeing progress in biocompatibility. The smart minds at VOCO Dental have developed a material called Admira Fusion, which has a unique makeup. Admira Fusion, simply put, is the world’s first all ceramic–based universal restorative material. There are no classic monomers such as Bis-GMA or UDMA.

Because it is ceramic based (utilizing Nano-ORMOCER), Admira Fusion has none of the drawbacks that resins do. Mainly that means there are no allergic reactions to any of the molecules patients are concerned about. However, the most impressive thing about the material is that because it is based on a ceramic, the long-term shade consistency is impressive. As we all know, glass doesn’t stain and, because of that, neither does Admira Fusion. Its esthetics are second to none the day it is placed, and it looks exactly the same 2 years later. For clinical situations where I need outstanding esthetics and want the confidence that it will look just as good in 5 years, I reach for Admira Fusion.

Wrapping Up

We have seen some impressive changes in our profession in the past decade. I think the truly amazing thing about the progress the profession has made is the wide expanse of subjects it covers. We have seen growth and intellectual leaps in a variety of topics.

When you stop and think about it, intraoral scanning, 3D imaging with cone beam computed tomography, in-office creation of things with mills and 3D printers, and artificial intelligence have all made remarkable progress in a very, very short amount of time. And yet, quietly in the background, the researchers and chemists have been hard at work creating ways that our restorative materials can better replicate nature.

As doctors, we are pretty lucky. We get to work with restorative materials that were the thing of science fiction not that long ago. Although I may never get to tell a patient that I can do as good a job as what they were born with, the scientists in dentistry are definitely closing that gap. The best thing is that we will all benefit from these advances. And that makes me look forward to the future.