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BACKGROUND:
Mercury, or Hg, is a neurotoxin that has been speculated to play a role in the pathogenesis of Alzheimer’s disease, or AD. Dental amalgam releases low levels of Hg vapor and is a potential source of Hg for a large segment of the adult population.

METHODS:
The authors studied 68 subjects with AD and 33 control subjects without AD to determine Hg levels in multiple brain regions at autopsy and to ascertain the subjects’ dental amalgam status and history. The subjects were from central Kentucky and Elm Grove, Wis. The authors conducted dental amalgam assessments during the lives of the majority of subjects and in some subjects at the time of autopsy only. The authors also determined three dental amalgam index scores–Event (placement, repair or removal of amalgam), Location and Time In Mouth–in addition to the numbers of and surface area of occlusal amalgam restorations. The authors determined Hg levels in multiple brain regions and performed full neuropathologic evaluations to confirm the normal status of the brain or the presence of AD.

RESULTS:
The authors found no significant association of AD with the number, surface area or history of having dental amalgam restorations. They also found no statistically significant differences in brain Hg level between subjects with AD and control subjects.

CONCLUSIONS:
Hg in dental amalgam restorations does not appear to be a neurotoxic factor in the pathogenesis of AD. The authors found that brain Hg levels are not associated with dental amalgam, either from existing amalgam restorations or according to subjects’ dental amalgam restoration history.

Recent studies have investigated a mercury-free silver alternative to amalgam, but the silver powders required a relatively high compaction pressure to consolidate. The aim of the present study was to consolidate a precipitated silver powder into a cohesive solid using an air-driven pneumatic condenser fitted with an amalgam plugger at a clinically realistic load, and to study the mechanisms and rates of three-body wear of the consolidated silver in comparison with that of an amalgam. The silver powder was annealed, rinsed with a dilute acid, and consolidated either in a prepared tooth cavity or in a specimen mold at a load of 15 N. A four-station wear machine was used where each specimen was immersed in a slurry containing polymethyl methacrylate beads, then a steel pin was loaded and rotated against the specimen at a maximum load of 76 N. The flexural strength in MPa (mean +/- SD; n = 10) was 86 +/- 20 for amalgam, 181 +/- 45 for silver with a polished surface, and 202 +/- 21 for silver with a burnished surface. After 4 x 10(5) wear cycles, the wear scar depth in microm was 134 +/- 54 for amalgam, 143 +/- 8 for polished silver, and 131 +/- 9 for burnished silver, which were not significantly different (Tukey’s multiple comparison test; family confidence coefficient = 0.95). SEM examination revealed cracks and fracture pits in the worn surface of amalgam, in contrast to a smooth surface in silver. Wear and material removal in amalgam occurred by microfracture and dislodgement of cracked segments, while wear in the silver occurred by ductile deformation and flow of materials. To conclude, the consolidated silver possesses a three-body wear resistance similar to that of amalgam, and a higher resistance to wear-induced damage and cracking than amalgam. The mechanism of wear in amalgam is microfracture and material dislodgement, while that in consolidated silver is ductile deformation and flow of material.

The goal of this study was to investigate the effectiveness of stand-alone modular air purification sys-tems in improving air quality in dental practices, hospital and laboratory environments. As air pollu-tant make-up and concentration may vary significantly in different indoor environments, the air clean-ing technologies utilised should be optimised for the pollutants targeted in a particular environment. Reduction of mercury vapours and formaldehyde were examined because of their importance for indoor air quality in dental practices. In addition, the reduction of particles and microorganisms was investigated as well as the removal of substances which are noticeable due to their strong odours. The air purifiers used in the study were configured to contain the most suitable air cleaning technology for each of the indoor environments. The systems use high-efficiency particulate air (HEPA/ULPA) filters, activated carbon-based filters with and without impregnation and/or activated alumina-based filters with impregnation. The maximum airflow of the systems ranges between 220 and 500 m3/h, depending on the filter configuration. The units were investigated under laboratory and simulated field conditions to determine removal efficiencies for various substances. High removal efficiencies for mercury vapour, formaldehyde, particles and microorganisms could be observed. The elimination of strong odours (orange oil, cinnamon oil and menthol) is difficult, if the source of the odour is not removed. The unit’s effectiveness in dental practices and in hospital treatment rooms will be analysed in follow-up studies including personal bio-monitoring investigations. The data will facilitate the evaluation of the role that optimised air purification systems can play in reducing pollutant exposure of medical personnel and patients.

Studies examining health consequences of the release of mercury from dental amalgams have concluded that there is insufficient mercury released from these restorations to cause a medical problem. Although the mercury vapor generated during removal of amalgams will cause a transient increase in the patient’s mercury level in tissue fluids, biochemical assays have demonstrated that the increase is too small to have a negative influence on organ systems. This is true even when patients have all their amalgams removed in a single session. Nevertheless, over the past decade, the release of mercury from dental amalgam has been frequently blamed for a variety of health complaints. A number of sensationalized media reports regarding the mercury issue have no doubt contributed to the public concern that has been aroused. Consequently, patients may present at the dentist’s office, either self-diagnosed or looking for a cause implicating mercury. In actuality, these patients may have symptoms of either medical problems or psychological disorders such as depression or anxiety. Unfortunately, the incorrect diagnosis may not only mislead, but actually place the patient in a dangerous situation. Two well-controlled studies have indicated that (1) 89% of the patients with self-reported “amalgam illness” had psychogenic disorders, whereas only 6% of the matched-pair manifested symptoms of these psychological disorders; and (2) these alleged “amalgam illness” patients had preneurotic reactive/defensive mechanisms that did not allow them to recognize aggressive and threatening situations which the control group would quickly and readily regard as potentially difficult to manage. Other studies involving psychological assessment seem to confirm that dental therapy (removal of amalgams) for people with alleged “amalgam illness” may, at best, provide a “placebo effect”.

Inflammatory cells in amalgam-associated, oral lichenoid contact lesions (OLL) were studied in 19 patients by immunocytochemistry using monoclonal antibodies. Ten of the patients displayed allergic patch test (PT) reactions to several mercury compounds and nine were negative. The immunocytochemical quantification showed a uniform composition of the inflammatory mononuclear cells in the two study groups. The number of HLA-D/DR-positive dendritic cells (P<0.001) and CD1a-positive Langerhans cells (P=0.035) was significantly lower in the PT-negative than PT-positive patients. HLA-D/DR expression on keratinocytes varied from negative to full thickness staining of the epithelium. HLA-D/DR expression in the full thickness of epithelium (3) or through the basal and spinous cell layers (2) was seen in 5 of 8 PT-positive patients, whereas none of the PT-negative patients had this staining pattern (P=0.045). These patients also showed a good clinical response after amalgam removal. Consequently, OLL may represent a true delayed hypersensitivity reaction with a trans-epithelial route of entrance of the metal haptens released from dental restorative materials.