Filling the gap: new data on safety of dental amalgams. (Environews Science Selections).

Controversy about the safety of dental amalgams--blends of mercury and other metals used in fillings--has been simmering for at least 150 years. An association between mercury vapor exposure and neurologic and neuropsychological deficits (such as decreased memory and attention, lowered response time, and tremor) has been documented among dentists and dental workers, who, in the course of their work, may be exposed to mercury vapor from amalgams. However, little research has been conducted on dentists' patients, who may not face occupationally elevated exposures but who have had varying numbers of dental fillings installed over the course of their lives. Could dental fillings leach mercury into people's bodies over time, eventually causing neurotoxic effects? According to a study by Pam Factor-Litvak of Columbia University and her colleagues, there is little cause for concern [EHP 111:719-723].

The researchers examined 550 healthy working adults aged 30-49 years to investigate whether having fillings was associated with reduced cognitive functioning, including verbal and nonverbal memory, attention, and fine motor coordination. The subjects participated in ah evaluation that included collection of urine samples to assess urinary mercury (UHg) concentrations, an oral examination to determine the type and number of fillings in each individual's teeth, a battery of standard neuropsychological tests, and a questionnaire designed to collect information about lifestyle, demographics, health history, and other pertinent characteristics.

The investigators used linear regression analyses to estimate whether there was an association between each exposure measure (UHg, total number of amalgam restorations, and number of occlusal amalgam restorations to align the upper and lower jaw) and neuropsychological test scores. The tests they administered were chosen to assess specific cognitive domains based upon reports of mercury-related neuropsychological impairments in occupational studies.

UHg concentrations were low among the participants, ranging from 0.09 to 17.8 micrograms per gram of the waste product creatinine (compared to a typical occupational exposure range of 2.0-60 micrograms per gram creatinine). The scores of the neuropsychological tests were within the norms for the ages studied and showed the expected relationships between factors such as age, sex, education level, and employment strata. The researchers found that neither UHg itself nor counts of either total or occlusal amalgams were associated with any measure of neuropsychological deficit.

According to the literature, impairment of function may be cumulative, occurring 20-35 years after exposure, and the researchers did consider the temporal relationship between the placement of amalgams and neuropsychological performance. Although they did not collect data about the age of the amalgams, they presumed that most of the fillings were placed 10-20 years prior to the study, because most fillings are first placed in the teenage years, with relatively few installed after age 25. This conjecture seems reasonable, although the authors acknowledge that the absence of those data is a limitation of the study.

This study may not lay the issue to rest once and for all, but as the authors conclude, their results "are reassuring in that exposure to amalgam-derived Hg is not associated with detectable subtle neuropsychological deficits."