Mercury from Dental Amalgam Fillings: Studies on Oral Chelating Agents for Assessing and Reducing Mercury Burdens in Humans

Failure of chelator-provoked urine testing results to predict heavy metal toxicity in a prospective cohort of patients referred for medical toxicology evaluation

INTRODUCTION

Provoked urine testing (PUT), involving chelating agent administration prior to measuring urine metal excretion levels, is used by some alternative health care practitioners to diagnose patients with heavy metal poisoning. Multiple medical societies have advised against this practice due to its presumed unreliability, expense, and lack of validation. However, no prospective study of the predictive value of PUT for heavy metal poisoning has been undertaken.

METHODS

This study utilized the Toxicology Consortium's prospective case registry to evaluate the reliability of PUT for diagnosing heavy metal poisoning. Inclusion criteria were toxicology clinic patients with PUT results who were subsequently evaluated by a board-certified medical toxicologist and had a determination made regarding whether their signs and symptoms were likely related or unrelated to toxicologic exposures. The primary outcome was the positive predictive value of PUT for heavy metal toxicity as diagnosed by the evaluating medical toxicologist. Patients presenting to participating toxicology clinics without PUT served as a comparison group.

RESULTS

74 of 106 cases presenting with PUT results met inclusion criteria and were analyzed. 15 cases were determined by the examining toxicologist to be likely related to a toxicologic exposure. Only three cases were found to be related to heavy metal exposure, giving a positive predictive value of 4.3%. 20.2% of patients with PUT were found to have signs or symptoms related to any toxicologic exposure, compared to 14.3% of clinic patients without PUT. Demographics of toxicology clinic patients with and without PUT results were not significantly different except for age.

DISCUSSION

Our results provide empiric support that PUT is an inaccurate predictor of a diagnosis of heavy metal poisoning by a board-certified medical toxicologist. Given the inability to properly interpret PUT results along with the increased cost burden and risk of false positives, PUT should not be performed.

Neuropsychological effects of low mercury exposure in dental staff in Erzurum, Turkey

OBJECTIVE

To carry out measurements of the Hg levels and personal exposure in Turkish dental clinics, and to evaluate possible adverse effects on the CNS in dental personnel.

SETTING

Five dental clinics (1 private, 4 public) in Erzurum, Turkey.

SUBJECTS AND METHODS

43, Hg vapour-exposed dental staff were examined and 43 hospital employees with no known exposure to Hg acted as the control group. Hg concentrations in plasma and urine were analysed by atomic absorption spectrophotometry. Possible effects on the central nervous system (CNS) were estimated by neuropsychological tests (Weschler Memory Scale-Revised (WMS-R) and Verbal Test of Memory Processes (VTMP)) and two self-administered questionnaires (Symptom Checklist-90-Revised (SCL-90-R) and Beck Depression Inventory (BDI)).

RESULTS

The dental staff group had higher whole blood (B-Hg) and urine (U-Hg) Hg levels than the control group. The mean B-Hg value was 2.18 nmol/l and U-Hg was 1.17 nmol/mmol creatinine. U-Hg had an inverse relationship with logical memory (in WMS-R test) and total retention score (in VTMP test), and a positive relationship with increased scores of Anxiety and Psychoticism (in SCL-90-R).

CONCLUSION

These results may represent long-term consequences of low Hg exposure. In dentistry, to decrease toxic effects, proper Hg hygiene should be practiced by all dental health care workers.