This randomized clinical trial aims to compare the effectiveness of three topical fluoride application protocols, namely three applications of a 30% SDF solution at yearly or weekly interval and three applications of a 5% NaF varnish at weekly interval, in arresting dental caries in the primary teeth of preschool children over 30 months.

This randomized clinical trial aims to compare the effectiveness of three topical fluoride application protocols, namely three applications of a 30% SDF solution at yearly or weekly interval and three applications of a 5% NaF varnish at weekly interval, in arresting dental caries in the primary teeth of preschool children over 30 months.

Preschool children attending the first year of the kindergartens will be invited to join this study. An invitation letter will be sent to the parents explaining the purpose and procedures of this study. Parental consent will be sought. Generally healthy children who have at least one tooth with untreated caries into dentine will be invited to participate and they will be followed for 30 months.

Dental clinical examination of the children will be conducted by a calibrated dentist in the kindergarten. Tooth and oral hygiene condition will be recorded. A parental questionnaire will be administered at baseline and at the 30-month follow-up visits regarding their children's socio-economic background and oral health related behaviours. The questionnaire will also assess parental satisfaction with their child's oral health and dental aesthetics.

All active dental caries lesions of the participant children will be treated if possible. The children will be categorized as having a high or a low caries rate. They will then be allocated by a stratified randomization method to one of the three study groups:

Group A - 3 applications of a 30% SDF solution at yearly interval Group B - 3 applications of a 30% SDF solution at weekly interval Group C - 3 applications of a 5% NaF varnish at weekly interval

A dental operator who is not involved in the examination of the child will apply the fluoride agents. Follow-up oral examinations will be conducted every 6 months in the kindergartens for 30 months. The status of the treated teeth and any possible side/adverse effects will be recorded in the follow-up examinations.

Inclusion Criteria:

• Generally healthy children who have at least one tooth with untreated caries into dentine

Exclusion Criteria:

• Children who have major systemic diseases or on long-term medication, are uncooperative or refuse the treatment will be excluded.