DENTAL AMALGAM AND ALTERNATE RESTORATIVE MATERIAL

Future Directions

 

Where To From Here?

Elizabeth D. Jacobson, Ph.D.
Chair, EHPC Working Group on Dental Amalgam

For the last 6 years, the U.S. Public Health Service has fixed its sights on the issue of potential health risks from the use of dental amalgam. One can and perhaps should ask the legitimate question of why. Certainly no public health disaster, such as occurred, e.g., with thalidomide or the Dalkon Shield, can be pointed to in the case of dental amalgam. In fact, with the millions of amalgam restoration procedures that have been performed over the past century, it could be argued that one could reasonably expect to see an increase in health problems within the treated population if the use of dental amalgam posed a risk, even in the absence of a scientifically designed data collection program. The plain truth is that no pattern of problems apart from rare and largely non-consequential allergic reactions has emerged.

Why then should the PHS continue to preoccupy itself with an issue that, from all indications, is receiving a level of attention disproportional to the currently-known risk level and an apparent low level of concern among most American consumers? Could PHS resources be better spent on other issues with comparatively greater impacts on the public health? These are tough questions, but the questions regarding the potential public health impact of the mercury component of dental amalgam are also tough, especially given the wide exposure of the public to dental amalgam.

For example, are patients treated with amalgam at any higher risk than those whose carious lesions are restored with different materials? Given what is known about potential toxicity from non-amalgam restorative materials, are people being exposed to greater risks than from amalgam fillings? Has scientific research conducted to date overlooked critical evidence of a public health risk from amalgam use, which most people apparently regard as negligible at worst? Is ongoing research headed in the right direction and likely to yield definitive answers? Should the PHS embrace a "zero tolerance" position with respect to amalgam risk, knowing full well that no medical product carries a guarantee of absolute safety and that the laws administered by FDA do not envision absolute certainty.

Perhaps the toughest question of all is when is enough enough? In other words, when can those entrusted with safeguarding the public health declare an end to an issue in which there is a modicum of public interest and concern? With finite resources, government cannot afford to keep everything on the "front burner." At the same time, science is methodical, time-consuming, and often controversial, particularly when it involves low-incidence phenomena. Those involved in research are accustomed to hanging in for the long haul. Yet in our fast-moving society, the general public has come to expect quick answers. These competing realities pose a special challenge for national health leaders and policy-makers. They must be able to convince an eager public of the worth of long-term research: that is, that such research is being done, not for idle intellectual curiosity, but to resolve important questions that bear on the public health and the quality of health care.

This is where we are with dental amalgam. The USPHS has committed to a broad-based program of research, education, and regulation, and has set as its standard the need for scientifically-based decision making. It is important that we stay on track with this program. But staying on track does not mean that our efforts should be focused exclusively on amalgam. Quite to the contrary, we must be equally vigilant with respect to all biomaterials used in dentistry for diagnosis, prevention and restoration in order to rapidly identify any untoward health effects that might arise from their use. Additionally, we must aggressively pursue new methods of dental treatment and oral health strategies and work cooperatively with the dental profession to effectuate change in oral health care delivery practices.

 

...And On To the 21st Century: Restorative Materials of the Future

Harold C. Slavkin, D.D.S.
Director
National Institute of Dental Research

We are on the threshold of the 21st century, a monumental event for science and humankind. In science we are poised for discoveries and their application which have the potential to change every aspect of how we view and address human health and disease. Within the next several years we will have a complete genetic blueprint of humans, extending the pioneering work of Watson and Crick. The impact of this information, which will be available to people of all ages on the Internet by the year 2004, rivals that of Einstein's theory of relativity, the now familiar e=mc2, as well as the monumental societal changes that occurred following the industrial revolution a century before that. In light of this new zeitgeist, as we review what the U.S. Public Health Service has accomplished over the past few years regarding dental amalgam and contemplate the future of research on restorative dentistry, I am struck by the words of G.V. Black who, in 1897, stood on the threshold of the 20th century and observed that "...the day is surely coming...when we will be engaged in practicing preventive rather than reparative dentistry...when we will so understand the etiology and pathology of dental caries that we will be able to combat its destructive effects by systemic medication."

While the introduction of fluoride as a preventive for the infectious diseases known as dental caries is one of, if not the, most significant public health successes of the 20th century, there are still individuals suffering from significant levels of dental caries. The poor and the elderly, children raised in areas of the United States who do not have access to fluoridated water or to information about preventive oral health care, and those who simply choose to ignore scientifically derived and sound advice are all subject to the ravages of this disease. And because of this there will be a continuing need to address health issues relating to this infectious disease.

We are now faced with the possibility that the ways in which we approached the solution to these oral and craniofacial health problems in the past have now been surpassed by a logic that has its roots in the intersection of cell and molecular biology, information sciences, mathematics, bioengineering, and materials and implant science. Collectively, this new approach has come to be known as biomimetics. The term, which evolved in the 1980's, simply means "to mimic biology" and is now synonymous with molecular technology, nanotechnology, genetic engineering, tissue engineering, and cell engineering. Within this rubric, the quest for us now becomes the design and fabrication of biological solutions to the oral health problems that we face in the clinic on a daily basis. And more to the point of this report, the application of biological approaches to restorative dentistry in the repair of tooth structure destroyed by the infection from Streptococcus mutans, the infectious agent responsible for dental caries.

Historically, inorganic materials such as dental amalgam have been used to restore enamel. Trained individuals find it relatively easy to use at room and body temperatures. It is relatively inexpensive, it is long lasting, and it withstands the environment and physical forces within the mouth well. However, non-biologically-derived materials like amalgam can be limited by their ability to "biointegrate" with tissues of the body and further, as discussed in various sections of this report, they may contain elements that are potentially toxic. Another of their shortcomings is that healthy tooth structure must be removed to prepare a site for their application. It is known that restored areas of the tooth, themselves, can become active sites for new infections thus creating a need for further surgical and mechanical approaches and destruction of yet even additional healthy tooth structure.

Alternatively, consider the emerging technology for tomorrow. Imagine, nationwide health promotion and disease prevention strategies that impact all American children. Imagine all children with access to fluoridation, health diets, dental sealants, and empowered with ideal oral health hygiene habits. Imagine early detection of initial enamel demineralization addressed with non-invasive remineralization technology. Finally, imagine the possibility of being able to utilize the sequence of genes and their gene products to design and fabricate the enamel bioceramic—to replace human enamel with human enamel. Even though the biological processes underlying this possibility are very complex, and the remaining steps in completing the biological issues required to produce enamel bioceramics are quite formidable, the biological and bioengineering communities are actually not very far from being able to realize the biomimetics of enamel bioceramics. For example, formation of enamel bioceramic involves the production of an organic template that is subsequently replaced by calcium carbonate and calcium hydroxyapatite crystals that are positioned along their c-axis resulting in the 99.6 percent inorganic enamel ceramic.

Significantly, NlDR-supported scientists as well as scientists in laboratories throughout the world, have identified and cloned the major enamel gene termed "amelogenin," which is located on the human X and Y chromosomes and which is responsible (when mutated) for X-linked inherited amelogenesis imperfects. Subsequent research has discovered a number of other enamel-specific genes and their gene products required for the design and fabrication of human enamel including sheathlin or ameloblastin (chromosome 4), and enamelin and tuftelin (chromosome 1). These genes when mutated are responsible for autosomal amelogenesis imperfects. At this time, the challenge for biomimetics is to learn how to make this bioceramic in an environment where the temperature is 37.5 C and the pH is 7.2, that is to say, in the mouth. The strategy is one of using molecular and nanotechnology to organize and orient, molecule by molecule, a pattern that promotes enamel crystal growth and orientation along the appropriate axis. With vision, innovation, creativity and sustained resources these possibilities can become realized and can become implemented within the diagnostic and therapeutic armamentarium of oral health professionals early in the new century.

Another area which shows progress addresses the clinical opportunities in which the infection from dental caries has fully penetrated from tooth enamel into the dentin, or in some instances has progressed as an infection into the dental pulp tissues. Present technology involves removal of the infectious material and destroyed tooth structures and tissues, often the use of "sterilization cleansing" techniques and dentin repair, or pulp tissue removal and the use if inorganic or inert biocompatible materials for root canal placement. To address these clinical challenges, a number of scientific advances now promise biological solutions to these complex infectious and inflammatory conditions. For example, NIDR investments in extracellular matrix molecules, biomineralization and growth factors has produced an enormous understanding of these processes and has identified a number of candidate molecules for biomimetics. We are now on the verge of using bone morphogenic proteins to stimulate cells found in the host pulp to differentiate into odontoblasts and to produce reparative dentin that is biologically functional and integrated into the dentin extracellular matrix that remains. Other possibilities from research on biomimetics extends beyond the treatment of diseased and destroyed tooth structure to include the development of diagnostics for subtle inflammatory processes. Imagine our ability to be able to accurately, precisely and safely assess oral health status without the use of ionizing radiation. Imagine our being able to precisely assess the extent of damage resulting from dental caries without the use of a probe.

Biomimetics provides remarkable possibilities well beyond the diagnosis and treatment of dental caries. Applications from biomimetics will play an important role in how we approach other diseases and conditions that affect the oral, dental, and craniofacial tissues of the body. The design of biologically compatible materials for the repair of temporomandibular joints that have been rendered useless by other treatment modalities or from the disease process itself; the treatment and prevention of inherited craniofacial diseases using our knowledge of genetics and biology; the development of new paradigms in the prevention, diagnosis and treatment of other infections of the oral cavity such as periodontal disease, opportunistic oral infections from Candida albicans associated with AIDS or other systemic conditions; and the development of alternatives to surgical placement of metallic implants in the treatment of edentulism using information from genetics and biology; all of these, will emerge in the 21st century from research involving biomimetics and will improve the oral health and hence the quality of life for all of our citizens.

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