Randomized controlled trial demonstrates that exposure to mercury from dental amalgam does not adversely affect neurological development in children.

SUBJECTS

The study subjects were 507 children (228 females and 279 males) from the Casa Pia school system in Lisbon, Portugal; the same cohort of children used in a previous study. The children were 8 to 12 years old at the time of enrollment in the study, which began in January of 1997. To be included in the study, a child must have had at baseline at least one carious lesion in a permanent tooth, no previous exposure to amalgam treatments, urinary mercury level less than 10 mg/L, blood lead level less than 15 mg/dL, IQ greater than or equal to 67 as obtained with the Comprehensive Test of Nonverbal Intelligence, and no interfering health condition.

KEY EXPOSURE/STUDY FACTOR: Study subjects were randomly assigned to receive dental treatment with either amalgam or resin-based composite for posterior restorations (and composite for all anterior restorations). By the end of year 1, the participants had a mean of 8.3 surfaces restored with amalgam, and the mean number of surfaces restored varied between 7.7 and 10.7 during the 7 years of follow-up.

MAIN OUTCOME MEASURE

The primary outcome measures for the study were the presence of neurological hard signs (NHSs), such as tremor, and the presence and severity of neurological soft signs (NSSs), such as synkinesias. NHSs were scored as present or absent. Tremor was reported separately from other NHSs because of its relationship to mercury toxicity. Observation of NSSs did not begin until follow-up year 2, so there were no baseline data for NSSs. NSSs were evaluated using the examination described by Peters et al, and each item was scored from 0 (absent) to 3 (maximum deviation).

MAIN RESULTS

Over the 7-year duration of the study, there were slight differences in the percentages of subjects exhibiting any NHSs (including tremor, which was reported separately) between the 2 treatment groups, but the directions of the differences were not consistent from year to year, and the differences were not statistically significant in any year. No statistically significant difference in NSSs--either percentage of subjects exhibiting NSSs or NSS severity scores--was observed between the 2 groups in any year.

CONCLUSIONS

The results of this study demonstrate that exposure to mercury from dental amalgam does not adversely affect neurological development in children.