The objective of this study is to compare the effectiveness of 25% AgNO3 solution plus 5% NaF varnish and 25% AgNO3 solution plus 5% NaF varnish with fTCP when applied semi-annually over 30 months in arresting dentine caries of primary teeth among preschool children. Half of Participants will receive topical application of 25% AgNO3 solution and 5% NaF varnish, while the other half will receive topical application of 25% AgNO3 solution and 5% NaF varnish with fTCP.

Aim:The objective of this study is to compare the effectiveness of commercially available of 25% AgNO3 solution plus 5% NaF varnish and 25% AgNO3 solution plus 5% NaF varnish with fTCP when applied semi-annually over 30 months in arresting dentine caries of primary teeth among preschool children.

Methods: The extension of the Consolidated Standards of Reporting Trials 2010 Statement will be followed for this 30-month, randomised, double-blinded, equivalence clinical trial. Approximately 2,000 kindergarten children will be screened and at least 376 children with caries will be recruited. This sample size is sufficient for an appropriate statistical analysis. 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 25% AgNO3 solution followed by a 5% NaF varnish with functionalized tricalcium phosphate (fTCP).Clinical examinations will be conducted at 6-month intervals to assess whether the caries are arrested (primary outcome). 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 5% NaF varnish with and without fTCP are equivalent in arresting dentine caries of primary teeth in preschool children when applied semi-annually.

Inclusion Criteria:

• have at least one tooth with cavitated dentine carious lesion

Exclusion Criteria:

• Children have severe forms of dental hypoplasia, under dental treatment or wearing orthodontic devices, have major systemic illness, and are on long-term medication.