|Jack D. Griffin Jr, DMD|
Jack D. Griffin Jr, DMD, reviews the history of bioactivity and discusses the possibilities that regenerative materials have in the future of dentistry.
Q: The word bioactivity is used all over in journals and product ads these days. What does it mean?
A: The word bioactivity itself simply means “to elicit a response from a living tissue.” That description is not a particularly good term for dentistry as that “response” could be either positive or negative. A word that better fits what we are looking for in an ideal dental material is regenerative. That meaning, “to provide an environment where tissues can heal,” is much more descriptive of the goal that many of us would like for dental manufacturers to currently focus on.
We are basically talking about materials that release ions (such as phosphates, calcium, and fluoride) that may participate in ion exchange with the tooth. If ions are released by the restorative material, in a form that can be used by the tooth, there is the potential to stimulate apatite crystal and secondary dentin formation.
Q: Is the term bioactive simply marketing hype, or are there substantial benefits to these products?
A: Bioactivity is not a new term; it has been described in dental materials as far back as 1969, when Hench talked about a “bioactive material” being one that elicits a biologic response and a biologic bond between tissues and the material. So, the concept is not really a new one.
The concept of replacing a human tissue with something more biologically acceptable is definitely a worthy goal. Today, we have materials that mimic the composition and physical properties of natural teeth and are relatively simple to use clinically with delivery systems with which we are already familiar. There is confusion though. Sometimes a manufacturer will combine regenerative materials with those that are not naturally bio-friendly, which results in claims of “bioactive” that cannot be substantiated. For example, many composites claim fluoride release but are seldom called bioactive because resins, although bio-tolerant, are not regenerative by nature. On the other hand, glass ionomers are often called bioactive because of fluoride release even though a major component, polyacrylic acid, is a pulpal irritant. As a result, we must rely on laboratory testing and scientific articles to evaluate ion exchange when looking at the potential to stimulate dentin repair.
Q: How do these materials actually work?
A: Available calcium (Ca) can stimulate cells involved in formation of mineralized hard tissue odontoblasts. The release of Ca at the pulp also enhances the activity of bone-associated proteins and pyrophosphatase, which helps to maintain dentin mineralization and the formation of new dentin bridging.
Preliminary evidence on the formation of apatite with a Ca silicate (Calsil) liner, Ca aluminate cement, mineral trioxide aggregate (MTA)-based products, and Ca hydroxide (CaOH) has been obtained. This evidence demonstrates that the phosphate ions of biological fluids dentinal fluids may react with Ca and OH ions given off from these materials and may result in apatite crystal precipitation. These properties form the mechanism by which bioactive/regenerative materials work to accomplish dentin formation.
Q: What is the history of bioactive/regenerative dental materials?
A: CaOH liners have been used in dentistry for decades in hopes of stimulating reparative dentin formation via high alkalinity, calcium release, and antimicrobial properties. In today’s adhesive world, CaOH liners are used less often because they can cause reduce restoration adhesion by having a zone of diminished bond strengths around the material and, in addition, there is the potential for voids underneath the restoration as CaOH dissolves from pulpal/dentinal fluids. As a direct pulp capping material, CaOH has had less-than-stellar results.
Calsils are another group of regenerative materials with a fairly lengthy track record. MTA has been used for many years as a dentin/cementum repair stimulator in various endodontic procedures including pulp capping and pulp replacement therapies. My last perforation was repaired successfully by an endodontist using MTA. Newer Calsil resin liners based on MTA science have shown high long-term sealing ability, antimicrobial capacity, dentin formation, and are more easily placed when compared to CaOH liners.
Q: What are we looking for in the optimal “regenerative” material?
A: It seems that almost every week a dental materials company comes out with another “me too” product. How many more nanohybrid composites do we need? How many more self-adhesive resin cements can we put in the drawer? Is there really an intense need for another flowable composite? With dental companies investing millions of dollars per year in dental research, we often see reinvented products that merely have a change in handling, aesthetics, or perhaps the way color is chosen. Obviously, all those are important but not usually that significant.
The ideal material would have a high pH to stimulate dentin repair, not be irritating to tissues, be antimicrobial, have moisture tolerance, release ions that can be used in hydroxyapatite formation, and have tooth-like physical and aesthetic properties. As added bonuses, not being soluble in saliva and ease of use with would be preferred. Hopefully, regenerative properties will dominate dental material research in the future.
Q: What regenerative materials are available today, and what does the future hold?
A: Currently, there are regenerative materials that fit in most material categories; these include liners, dentin replacements, cements, and direct restoratives. A Casil liner may be the simplest to incorporate into an existing restorative arsenal as a thin layer can be placed that seals, insulates, resists microbes, and provides an insulation layer under any current restoration techniques. For cements, research and electron micrographs have shown apatite crystal formation and margin closure between our indirect restoration and the tooth.
Regenerative ionomers that release high levels of Ca, phosphates, and fluoride have been excellent dentin replacements and even have been impressive in occlusion. These materials have done excellently as a pediatric filling material and in conservative Class I, II, and V cavities in adults. Perhaps their greatest strength has been in the role that traditional glass ionomers have served with a greater regenerative potential. All of these “newer” materials now have several years of clinical and laboratory evaluations with very high evaluations and clinical success.
The restorative dental future continues to become brighter and brighter as we search for materials to provide “optimal” dentistry. Hopefully, the focus will now be on materials that provide an environment where tissues can heal, give less sensitivity, and also increase the longevity potential of our aesthetic restorations. Many forward-thinking companies are currently doing active research in this area.
Dr. Griffin completed a general practice residency and maintains a general practice in Eureka, Mo, that focuses on efficiency in almost all phases of general dentistry while providing state-of-the-art care for affordable fees. He enjoys teaching practice efficiency and predictable posterior techniques and is open to teach courses for groups or to raise money for charity. He can be reached via email at firstname.lastname@example.org or via the website eurekasmile.com.