Water Journal : Water Journal April 2012
wastewater technical features 144 APRIL 2012 water Research presented researchers' views and findings expressed at the National Institute of Health Technology Assessment Conference on Effects and Side-effects of Dental Restorative Materials (Arenholt- Bindslev, 1992). This conference appears to be the genesis of formal international concerns regarding the environmental effects associated with dentists removing and inserting amalgam. While several European nations had previously set compliance standards for separators, in 1999 the International Standard Organization set Standard 111 43. It warrants a minimum (mass fraction) retrieval of 9.5mg from 10gm of amalgam particles suspended in a one-litre solution of water containing sodium pyrophosphate as a dispersant to minimise the formation of air bubbles. Particle size distributions measured by largest dimension must be: 60% mass fraction equal to or less than 3.15mm and greater than 0.5mm; 10% mass fraction equal to or less than 0.5mm and greater than 0.1mm; 30% mass fraction equal to or less than 0.1mm. A minimum 95% retention has to be achieved when the litre of suspension is passed once, at a uniform rate spanning 2 minutes, through the separator. The calculation of efficiency is executed three times at empty (0% of fill) and peak (70% of fill) level. Compliant separators operate on either one or more of the following principles: gravitational sedimentation; filtration with networks, membranes, slats and granules; and water-driven centrifugation. Some later models incorporate an ion exchange system. The first formal evidence for separators also appeared in the Australian dental literature in 1999. In February, a Working Party from Australia's peak health advisory body, the National Health and Medical Research Council (NHMRC), published "an informed position statement on the health effects of dental amalgam and mercury in dentistry" (NHMRC Working Party, 1999). It commented peripherally on the NHMRC's guidelines for disposal of amalgam. By December, The Australian Dental Journal had published the NHMRC Working Party Chairperson Professor John Spencer's "Dental Amalgam and Mercury in Dentistry" and Chin et al. 's "The Environmental Effects of Dental Amalgam" (Spencer, 1999). At this time, as detailed hereafter, there were operational issues and reservations regarding separators. Nonetheless, both Spencer and Chin et al. provided evidence that endorsed the need for separators in dental surgeries across Australia. Dentists' Use of Amalgam Contention regarding amalgam has persisted within and outside the dental profession for over a century. Amalgam does not fit the profile for an ideal restoration: no material does. In the 1980s, a number of investigators authoritatively confirmed that amalgam contributed to the mercury burden of dentists and patients. These and associated discoveries reinvigorated European and North American dental research into both mercury and amalgam. These investigations focused not only on the influence of amalgam-derived mercury and derivatives in human physiology and pathology, but also on general environmental concerns. This background fuelled public debate about the safety of amalgam, which evolved into manufacturers' promotion of and patients' demand for alternative restorative materials. Social and political sensitivities regarding amalgam were growing. In contrast to European and North American trends in research, Australian investigations into amalgam declined after the 1980s. There are several explanations. Throughout the 1990s, highly acclaimed Australian research focused on promising non-amalgam materials, such as composite resins and glass ionomers. These cannibalised interest and competitive bids for sparse funding of dental research. Moreover, significant evidence confirms that amalgam was being phased out of dental practice. For example, in Australia between 1983 and 1997, the placement of amalgam fillings nearly halved. In 1997-- 1998, Australian dentists used amalgam in only 28% of restorations (NHMRC Working Party). In 2002, another Australian study involving 560 dentists reported that 59% of participants had decreased their use of amalgam over the preceding five years. This decline in amalgam use reflected patient demand for aesthetic restorations, the widespread acceptance of adhesive (non-amalgam) dentistry, changing patterns of dental caries in the community and paradigm shifts in both caries diagnosis and management. Public opinion regarding mercury in amalgam was another factor that influenced dentist-patient selection of the restorative material. In 1995, a widely circulated Australian study, involving 5,101 subjects, confirmed that 37.5% of dentate respondents were concerned about mercury in fillings (Spencer, 1999). Explanations involve conjecture but anecdotal evidence suggests: perennial post-1875 warnings about dentists' "poisoning of thousands of people all over the world"; the aforementioned physical and chemical properties of mercury; escalating environmental awareness and concerns about anthropogenic pollution; mass poisonings, such as the consumption of fish and shellfish contaminated from perennial discharge of industrial waste into Minamata Bay (Japan); and even Lewis Carroll's dyskinetic character "The Mad Hatter". For whatever reason, in significant sections of the community, amalgam has a public image problem. Again evidence is anecdotal, but throughout the 1990s many dentists in Australia believed that amalgam was on the cusp of extinction. Despite a plethora of research into alternative materials, in 2012 the dental profession still needs amalgam. It remains "the most widely used and widely taught direct restorative material for load-bearing posterior restorations". Echoing endorsements from many dental organisations and Dental amalgam has been used for well over half-a-century.
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