How bioactive materials are changing restorative dentistry

June 21, 2018

Article

Materials marketed as ‘bioactive’ serve to solve a long-standing problem in dentistry - giving teeth what they want.

Materials are a fascinating, ever-changing, ever-improving facet of restorative dentistry. For more than 100 years, amalgam fillings have been commonplace. And while they’re still in use (albeit, not as often), the introduction of resin composites seemed to correct what amalgam left to be desired - a mercury-free material that also was tooth-colored. Bioactive materials serve to improve materials even further.

“Bioactive materials help clinicians transition from a repair model to a prevention model,” says Fred Berk, president of Pulpdent. “Composite restorations fail due to microleakage and the degradation of the adhesive layer. This usually appears as staining at the margins. Bioactive materials have a great potential to seal against microleakage and slow or prevent the progression of secondary caries under restorations. This is a great benefit to the patient and results in longer-lasting restorations and preservation of tooth structure. Bioactive products like ACTIVA BioACTIVE provide the esthetics, strength and wear resistance of composites, and release and recharge calcium, phosphate and fluoride, while promoting a healthier dentin interface over time.”

What does ‘bioactivity’ mean?

The word “bioactivity” can mean different things to dental providers and manufacturers, which can lead to some confusion.

“Bioactivity is sort of a buzz word in dentistry right now,” says Dr. Jason Goodchild, DMD, director of clinical affairs for Premier Dental. “You hear a lot about it; a lot of manufacturers promote it as a part of their materials. I think the concept is nebulous, making manufacturer’s claims hard to verify.”

Dr. Nathaniel Lawson, DMD, is director of the division of biomaterials at the University of Alabama at Birmingham School of Dentistry. In conjunction with the American Dental Association (ADA), he conducted a survey of 400 dentists, seeking their definition of “bioactive.” The dentists were asked: Is it something that can release ions to prevent cavities around a filling; something that can help grow reparative dentin if there’s pulpal damage; or is it something that can grow hydroxyapatite on the surface to help seal any gaps between the filling material and the tooth that’s next to it?

“Most people thought it was either inducing formation of reparative dentin or releasing an ion,” Dr. Lawson says. “Ion release isn’t anything new because that’s what resin-modified glass ionomer and fluoride-releasing materials have been doing for a long time. The novelty is sometimes that these materials release calcium and phosphate as well. Healing the pulp is not something new. That’s something like a Dycal (calcium hydroxide) material has been doing for a long time.”

That confusion, Dr. Goodchild says, likely stems from a lack of consensus.

“I think there isn’t an accepted definition of what bioactive means,” Dr. Goodchild explains. “You hear a lot of definitions, however, in its simplest form, ‘bioactive’ may mean something like, ‘A material that has biologic effect on the surrounding tissue.’ Other definitions may indicate that the material remineralizes or strengthens tooth structure by releasing fluoride or other ions, like calcium, phosphate - or maybe all of them together.

“‘Bioactive’ may mean that the material is capable of regrowing tooth – hydroxyapatite – as is believed with calcium aluminate materials,” he continues. “It also may mean that the materials help promote healing of tissue, following pulp capping procedures, which historically have involved materials like MTA or one of the very oldest materials for bioactivity, calcium hydroxide.”

The use of the word “bioactive” with modern materials is somewhat of an overreach, Dr. Lawson believes.

“I think that ‘bioactive’ is a marketing term,” he says. “You can talk about either ion-releasing or pulp-healing materials. Some people want to define ‘bioactive’ as a material that can grow hydroxyapatite on its surface. This definition is more applicable to dental implants. Those are placed into bone, and if you have hydroxyapatite grow on the surface, then you can have osteoblasts grow on the hydroxyapatite and form an actual connection with the bone. But that’s something no filling material can have because it’s not in contact with bone, it’s in contact with tooth, which doesn’t have any cells in it that are capable of forming a bond with hydroxyapetite.”

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Serving a purpose

Materials marketed as “bioactive” serve to solve a long-standing problem in dentistry - giving teeth what they want.

“Very simply, if you think about what a tooth really wants, you think about the disease process itself,” Dr. Goodchild explains. “Bacteria in dental plaque feed on sugar and release acids that demineralize the tooth, which can lead to cavitated lesions. After removing the affected tooth structure, dentists should consider what material would be best suited to restore what is lost. Caries and the trauma to the tooth associated with removing it can be injurious to the tooth. Bioactive materials can be a way to not only restore the cavity but help provide a mechanism for healing, health and improved function.”

Existing materials, obviously, get the job done, but they’re not ideal.

“A tooth doesn’t really want a metal filling that’s amalgam,” Dr. Goodchild says. “Even though amalgam restorations have had tremendous success for well over a hundred years in dentistry, you’ve heard the mercury debate. Whether or not there is something there, there is always a balance between efficacy and safety. Furthermore, I have seen a decrease in the use of amalgam in my practice not so much for safety concerns, but rather because patients request more esthetic options.”

Resin composites can be an improvement over amalgam, especially esthetically, but there also may be concerns.

“Or do [teeth] want plastic, which is resin composite?” Dr. Goodchild continues. “In many cases that involves bis-GMA resin technology, which includes Bisphenol A (BPA) as an ingredient. There is controversy around whether BPA can be released after placement and curing of these resin composites, but you mention BPA and patients can get upset.”

Other materials seem to be more agreeable to teeth.

“Then you talk about things like glass ionomers, which, since the 1970s, have been in that sort of middle ground,” Dr. Goodchild says. “It’s not resin composite, and there is some fluoride release. It does chemically bond to tooth structure without additional adhesive. Then came resin-modified glass ionomers, which replaced polyacrylic acid with polymerizable monomers. This gave us the materials that were a hybrid between a resin composite and a glass ionomer – this can also include compomers and giomers. So, is that the right answer for an ideal restorative material that promotes healing and health? And now there are newer types of hybrid materials that are resin-based but have some glass ionomer components to them. A good example are the ACTIVA products from Pulpdent. So, this is a very wide-ranging question.”

Dr. Goodchild and his colleagues at Premier Dental have a new microencapsulated resin that fits into this category.

“We have a new sealant called BioCoat™, and we are using a new technology,” he explains. “It’s very novel, developed in partnership with Creighton University School of Dentistry, where we are using traditional resin technology and are able to microencapsulate ions – fluoride, calcium and phosphate – which kind of makes it the first bioactive composite resin.”

As bioactive materials evolve, they become more effective and easier to use.

“Materials for treating the pulp, such as the MTA-based liners, TheraCal LC^® or Biodentine^®, are changing the market because their active ingredients have been around for a while, but they’re now in a form that is easier to use,” Dr. Lawson says. “TheraCal LC is a material I use all the time if I have a really deep filling that is close to the pulp. I’ll put the TheraCal LC over the deep part of the preparation, and it’s just easier to use than a material like MTA or Dycal, which is a material that has been around for a long time. Biodentine is another bioactive material that’s popular. It’s a liner and a temporary material all in one. With the restorative materials, like ACTIVA, or cements, like TheraCem^® or Ceramir, I think of them as another kind of ion-releasing material, similar to glass ionomers, but they also release calcium as well as fluoride.”

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Indications

Like any material, its usage depends on the product and the indication.

“Not all bioactives are the same,” Dr. Lawson observes. “For instance, there are three or four bioactive cements and they’re all different. Some are resin-based, so they are more retentive but would also be more moisture sensitive and release fewer ions. Others are non-resin-based, which gives reciprocal advantages and disadvantages. As far as restorative materials, there’s really only one on the U.S. market that claims to be bioactive.

"I would use the cements and restoratives, in cases of higher caries risk patients, where you think that you want to have some additional ion release," he adds. "With the liners, I would use them in place of traditional liners, just knowing that the handling is a little bit easier. Based on the ADA survey, liners seem to be the most frequently used bioactive materials.”

Bioactive material usage will also depend largely on the patient and his or her restorative need. For instance, these materials tend to be more hydrophilic, so they’re ideal for certain patients.

“A lot of my colleagues use bioactive materials on a daily basis,” Dr. Goodchild says. “The easiest answer for when I use them the most is on kids. A lot of the bioactive restorative materials are a little more water-friendly, which means they can be placed in a not so pristine environment, and children’s’ mouths generally fit that criteria. It’s not always easy to keep a child’s mouth open and dry while you do all this dental work.”

Those patients who are prone to caries are also ideally suited for bioactive materials.

“A person who has a high caries rate or a lot of tooth decay would probably be someone I would use a bioactive restorative material,” Dr. Goodchild says. “Additionally, for patients with large carious lesions, I would consider a bioactive base/liner for the release of ions. Maybe you put a traditional, non-bioactive type material on the occlusal surface, but you consider a material like TheraCal LC or Lime-Lite™ as a base/liner to help stimulate healing. Along the root surfaces, bioactive materials can also be very good. Older individuals who may suffer from hyposalivation can also benefit from bioactive materials because they may end up having high caries rates.”

And in some cases, bioactive materials can be used for the entire procedure.

“You can run the gamut,” Dr. Goodchild says. “If you’re talking about simple restorative fillings, you can probably do a bioactive solution from start to finish.”

Choosing the best bioactive material, Dr. Lawson says, involves the same decision-making process used for conventional materials, along with some specific research.

“Aside from normal properties that you would look for in any material - mechanical and esthetic properties - to measure bioactivity, there are a couple of extra tests I would want to look for,” Dr. Lawson says. “If it’s a material that goes in contact with the pulp, there have been studies that have looked at what they call dentinal bridging, or the formation of reparative dentin over the pulp. If you’re talking about a restorative material, like a cement or a filling material, the two things that I would want to see are making sure that it releases at least calcium, and then you’d want to look to see if there have been any studies to show that if you place this restoration in the tooth, does it in fact decrease the incidence of cavities around the margin, either in a lab test or in a clinical trial. Although there have been studies which show experimental calcium-releasing materials can inhibit demineralization of surrounding tooth structure, there hasn’t been a lot of research for commercially available bioactive products, to be honest.”

Bioactives versus conventional materials

While bioactive materials ameliorate some of the problems with resin composites, they too have their downsides.

“There are going to be some trade-offs,” Dr. Goodchild says. “What you give up in bioactivity with resin composites, you gain back in terms of wear potential and physical properties. You’re certainly going to give it up these things if you use a glass ionomer product. The materials that have both resin composite and glass ionomer components help to mitigate the trade-offs, but even if you move into resin-modified glass ionomers, you’re going to give up esthetics and strength. That’s why, historically, those materials haven’t been used in the posterior because they just don’t hold up to occlusal forces.”

Ultimately, it becomes an issue of weighing the pros and cons.

“There’s always a balance when selecting materials. We are always considering the right material for the right patient and situation,” Dr. Goodchild adds. “If you want the material with the highest physical properties, the best esthetics, you’re probably still looking at traditional composite. If you want some middle ground, you have some with the resin modified glass ionomer products from GC America and others, Giomers such as Shofu’s Beautifil and Pulpdent’s ACTIVA restorative.

“When you’re talking about anterior work, where esthetics is going to be the most important criteria, you probably still are looking at traditional composites,” he continues. “I don’t think we’ve gotten to the point where you’ve married everything into one ideal product. It’s still a little bit of give and take.”