The benefits of ion releasing, bioactive cements and adhesives.
One of the latest buzzwords in dental materials is “bioactive." In essence, that means the cement provides the raw materials needed to strengthen and regenerate enamel. That doesn’t mean, however, using these materials will lead to the regrowth of an entirely new tooth, but they do promote an environment in which a certain amount of ovary minerals issue can occur.
So, what really happens with ion-releasing bioactive materials?
“When tooth enamel demineralizes, we lose calcium and phosphate,” says Dr. Jason Goodchild, DMD, director of clinical affairs for Premier Dental. “When you replace lost calcium with fluoride to form fluoroapatite, you’ve strengthened that tooth and you’ve given better protection against acid attacks. The thinking was if we have materials that have fluoride in them, they are then reservoirs for fluoride when demineralization occurs. You’ve got fluoride readily available, which then gets taken up by the enamel, and it becomes a stronger tooth. To do that, there needs to be calcium and phosphate around as well.
"Historically, saliva has been the reservoir of calcium and phosphate and together with the fluoride in the restorative material or preventive varnish, it becomes the building block to help remineralize the tooth," he continues. "We’ve done great for a long time, just providing fluoride, but we can do even better if we provide all those things together. There are a lot of materials now that have calcium and phosphate in them. We’ve done that in a lot of hygiene products toothpastes and varnishes. We’ve even got them in some restorative materials, like ACTIVA, TheraCal, and Lime-Lite, where we tried to put it all back together and give the tooth all the building blocks to repair itself.”
In addition to their cementation duties, bioactive cements provide the added benefit of potentially strengthening enamel, which is especially desirable in patients at high risk of caries. “I can't see a disadvantage of using a cement with ion release, as long as none of its other properties are compromised,” Dr. Nathaniel Lawson, DMD, director of the division of biomaterials at the University of Alabama at Birmingham School of Dentistry says. “Assuming that all the claims of the cements are true, of course these properties would be most beneficial to the high-caries risk patient.”
If deciding whether or not to use a conventional cement or one with bioactive properties in which all of the qualities are the same, choosing one with ion release is an added benefit. “If you have two materials-one is bioactive and one is not-they both perform equally well in their role, and are equally easy to use, why wouldn’t you want to use a bioactive?” Dr. Goodchild observes.
“Another way to think about crown and bridge is when you deliver a crown to a patient, it’s not the end of the procedure; in fact, it’s the start of the procedure," he adds. "We finished the dentist’s side of it, however, that’s just the beginning of the crown’s clinical life. To give that crown a great start for its clinical life, why wouldn’t I want to give it ions to help the tooth repair itself and be happy and healthy?”
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But are bioactives equal to their conventional counterparts? If they exist within the same cement category, then, yes, Dr. Goodchild affirms.
“There are so many different types of cements and categories of cements, if you’re thinking about a bioactive cement like Doxa or Calibra Bio or ACTIVA, in the concept of their same category, then I would say yes,” he says. “Doxa versus an adhesive resin cement, then you give up esthetics. Looking at cements within the same category, I think is comparable.”
Ion release is a beneficial property, but there is some confusion over what to call those materials. There is some thought the term “bioactivity” is more for marketing than anything else. However, that criticism may be because the field is somewhat new and the proper phraseology has not yet been applied.
“Is bioactive the right word? Is it biocompatible? Is it bioreactive?” Dr. Goodchild ponders. “There was some confusion about that word, because I think it’s kind of an interesting idea.”
He references ADA News from June 2018 which reads, “The ability to release ions, including those present in tooth mineral, is a property associated with being ‘biointeractive’. Ions released from a ‘biointeractive’ restorative material or cement may enter saliva, driving the process of remineralization in surrounding tooth structure. Some materials can be both ‘bioactive’ and ‘biointeractive.' Additionally, calcium release and pH effects from a bioactive liner in contact or close to the pulp could cause the release of growth factors entombed in dentinal collagen, thereby stimulating odontoblasts to form reparative dentin.”
“We’re not completely sold on the idea of what the right word is,” Dr. Goodchild continues. “Is it bioactive? Biointeractive? I think the catchall people use nowadays is bioactive. This is still an evolving concept.”
The terminology, he observes, may be different for clinicians than those in other disciplines, like research.
“For all intents and purposes, the clinician probably just thinks of things like bioactivity,” he says. “It’s something in the cement I’m going to use that is going to react and will be favorable to the tooth’s environment. It’ll do what it is supposed to do-act as a cement and perform-but also contain things the tooth may need to help restore or repair itself, when you get into things like calcium, fluoride or phosphate.”
Sometimes, having less is actually providing more.
“On the other side of the spectrum, it doesn’t contain things the tooth or body doesn’t need,” Dr. Goodchild says. “We understand amalgam has been used in dentistry for many years,and has been very successful. However, it’s metal and metal contains mercury-which shouldn’t be in the body.”
Bioactives may enjoy an element of novelty because they are so new, but do they live up to the hype? How successful are bioactives? To some extent, the jury still seems to be out.
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“There are several potential benefits of ion release from a cement, although not all benefits have strong evidence,” Dr. Lawson says. “First, an ion-releasing cement could potentially prevent caries at the margins of a crown by releasing ions favoring remineralization over demineralization. Despite the widely held belief in this clinical benefit, there is not as much evidence as you would think. Another potential benefit is these ion-releasing cements can grow hydroxyapatite on their surface.
"There are two potential clinical benefits of this feature of the cement: One, if there is an open cement gap, hydroxyapatite can grow on the surface of the cement and close the gap, and two, if hydroxyapatite is grown on the surface of the cement in contact with tooth structure, this hydroxyapatite can seal the interface between the cement and the tooth, similar to the corrosion products formed with amalgam," he continues. "A final benefit of ion release is a calcium-releasing cement may be able to cause the release of growth factors that in turn form reparative dentin, similar to what can happen with calcium silicate liners.”
“It’s hard to see what those effects could be,” Dr. Goodchild adds. “They’re almost intangible to the clinical dentist. You put fluoride in which help to remineralize and prevent caries. That’s hard to see and hard to measure. Additionally, there are so many other factors at play. We’ve been doing fluoride varnishes on people’s teeth. We do restorations that contain fluoride, like glass ionomer. The best we can do from the dentist’s side is to use great materials which, hopefully, give us a belt-and-suspenders approach. Not only do they perform well, they provide an added benefit that could help prevent caries or failure.
"There are other factors at play here," he continues. "Even if I use the best materials, the most effective bioactive materials, the patient still has to do their part too. Each patient is different and they have their own chemistry, their own oral hygiene habits, their own medical history-they may take medications that cause dry mouth. Dentists want to use high quality materials that have that belt-and-suspenders approach, but without the patient doing their part, it’s all going to fail anyway.”
For the clinician, in addition to whatever benefits bioactivity may offer, their underlying formulation makes them easy to handle, which is yet another benefit.
“Many of these materials are really based on glass ionomer technology,” Dr. Goodchild says. “Newer materials: calcium aluminate, calcium silicate materials, really do take their roots in glass ionomer. We built on that technology because historically, resins haven’t always been the greatest way to present a bioactive material. Ionomer technology was probably where we started this with fluoride release, to hybrid materials that have a little bit of resin, and finally having resins that are considered bioactive.
“Most of these materials, if I use Doxa Ceramir, as an example, are fairly easy to use,” he continues. “Their esthetics haven’t always been wonderful. I think we are changing. Technology moves so fast, just trying to stay up with all these materials is interesting and challenging.”
Bioactivity may be an appealing trait, but a product’s selection should not be solely based on that feature.
“With the materials currently available, their selection should be based on their properties unrelated to ‘bioactivity,'” Dr. Lawson observes. “For example, there are calcium aluminate cements, such as Ceramir or Calibra Bio, that have more moisture tolerance and easier clean-up than resin cements, but don't have as high of retention. Whereas, there are other cement, like ACTIVA bioactive cement or TheraCem, that are resin cements, so they have a little higher retention, but must be used with good isolation, like any resin cement.”
As beneficial as bioactives seem to be, they’re just one variable in the larger equation of restorative success. There are still plenty of other factors that can make or break the case.
“Whenever we talk about picking cements, I always try to remind practitioners picking a cement is just part of an overall procedure,” Dr. Goodchild says. “If you haven’t done those other pieces correctly, cement is not going to fix it. If you haven’t treatment planned it right; if you haven’t prepared the tooth correctly; if you haven’t taken an impression digitally or with an impression material the right way; the lab hasn’t done their job; this is just a part of it. If everything goes to plan, then the cement you choose, when you choose it correctly, it’s going to do just what you intend it to. But if you haven’t prepared correctly, maybe you’ve over tapered the crown, and then you want to use something to glue it in, it doesn’t matter what you use, it’s probably not going to work. Cement selection is vital, but it’s just, simply, one part of the bigger procedure.”