 Background: Tooth decay in children Early childhood caries, or ECC is a common childhood disease. Poor dentition significantly affects the nutrition, growth, development and general health of children. Conventional dental care for ECC is neither affordable nor accessible, particularly for the disadvantaged communities. Silver diamine fluoride SDF is a safe, cost-effective caries-arresting agent that appears to conform to the World Health Organizations Millennium Goals. SDF is commercially available at 38 and 12, and topically used yearly or half-yearly to arrest ECC. The SDF regimens used for ECC treatment lack an evidence base. Therefore it is necessary to find the most suitable SDF concentration and application interval to arrest ECC. The purpose of this randomised controlled trial is to compare the efficacy of two commercially available SDF solutions at pre-prepared concentrations of 38 and 12 when applied at yearly or half-yearly intervals over 36 months in arresting caries in primary teeth. 