The Children's Amalgam Trial: design and methods

The safety of silver amalgam as a dental restorative material has been controversial since its introduction 150 years ago, but until recently it has been assumed that the exposure to mercury from dental amalgam is limited to the acute placement phase. However, some recent studies have raised safety concerns by demonstrating chronic release of mercury vapor from amalgam fillings during chewing and brushing. The Children's Amalgam Trial is a two-arm randomized trial of safety, comparing amalgam with a mercury-free restorative material. A single masking procedure is used to ensure that all investigators and staff measuring outcomes are unaware of assigned trial arm. The study follows 534 New England children, aged 6–10 years at enrollment, for 5 years. The children were recruited from two northeastern U.S. communities, one in rural Maine and one in urban Massachusetts. No trial subjects received prior amalgam restorations, and all were in need of at least two posterior occlusal fillings. Participants were randomized to receive either amalgam or composite material for all posterior restorations at baseline and at subsequent visits. The primary endpoint will be 5-year change in IQ scores. Secondary endpoints will include measures of other neuropsychological assessments and renal functioning. This paper describes the design of the Children's Amalgam Trial and includes data on baseline characteristics of the subjects.