• Aim: This randomised controlled trial will systematically compare the efficacy of a 25% AgNO3 solution followed by 5% NaF varnish with that of a 38% SDF solution in arresting caries teeth among preschool children when applied at half-yearly intervals over a 30-month period.
• Method: The extension of the Consolidated Standards of Reporting Trials 2010 Statement will be followed for this 30-month, randomised, double-blinded, non-inferiority clinical trial. Approximately 2,400 kindergarten children will be screened and at least 826 children with caries will be recruited. This sample size is sufficient for an appropriate statistical analysis (power at 90% [β=0.10] with a 2-sided type-I error of α=0.05), allowing for a 18% drop-out rate. The children will be randomly allocated into 2 groups to treat their caries over a 30-month period: Group A - biannual application of a 25% AgNO3 solution followed by a 5% NaF varnish, and Group B - biannual application of a 38% SDF solution followed by a placebo varnish.Clinical examinations will be conducted at 6-month intervals to assess whether the caries are arrested. Information on confounding factors such as oral hygiene habits will be collected through a parental questionnaire.
• Possible results and implications: As the first of its kind, this study would help to determine whether AgNO3 followed by NaF is at least as effective as SDF in arresting childhood caries. If so, because 25% AgNO3 and 5% NaF contain less silver and fluoride, respectively, than 38% SDF, their use would be more favourable than SDF in young children.

Inclusion Criteria:

• Kindergarteners who have joined our outreach dental service will be invited to join this study. Preschool children aged 3-4 years who have tooth decay and are attending the first year of kindergarten will be invited to join this study.

Exclusion Criteria:

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