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 Organization's 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.

Methods / Design: This double-blinded study has recruited 888 kindergarten children aged 3-4 years with caries. The sample size is sufficient for the appropriate statistical analyses. The children were classified into high and low caries rates and equally allocated into four groups for the caries treatment:

Group A - semi-annual application of 12% SDF; Group B - annual application of 12% SDF; Group C - semi-annual application of 38% SDF; Group D - annual application of 38% SDF. The children will be followed for 36 months in their kindergartens until they enter primary school. Clinical examinations at 6-month intervals will be conducted to assess whether the caries are arrested. Information on confounding factors, such as oral hygiene habits and the use of other fluoride agents, will be collected through a parental questionnaire at the baseline and follow-ups.

Discussion: This study will help determine the most suitable SDF concentration and application interval to arrest caries in children. Because SDF use for caries arrest is painless, simple, and low-cost, it can be widely recommended and promoted for caries control in young children or those with difficulty accessing and affording conventional dental care. The applicability of the findings and their impact on public health would be immense.

Inclusion Criteria:

The children included in the study should

1. aged 3-4 years who have tooth decay and are attending the first year of kindergarten,
2. be generally healthy,
3. have parental consent, and
4. have at least 1 tooth with untreated caries that extends into the dentine.

Exclusion Criteria:

• Children who are uncooperative and difficult to manage, have major systemic diseases, or are on long-term medication will be excluded.