Background: Early childhood caries (tooth decay, ECC) affected 55% 5-year-old Hong Kong children, and 70% of these children had gross destruction of the upper anterior teeth with negative long-term impacts on health and quality of life. The existing standard of care for prevention of ECC, topical application of 5% sodium fluoride (NaF) varnish, is inadequate. In Hong Kong and other parts of the world, 38% silver diamine fluoride (SDF) solution, applied topically to cavities, is used to arrest ECC. Work published by our research group suggests it likely also has a preventive effect of ECC. Moreover, SDF has been shown to be preventive in tooth decay in permanent teeth. Nevertheless, no pivotal clinical trial has been performed to support a change in usual practice.

Aim: This is a Phase II single-centre randomized, double-blind, active-controlled, parallel-group pragmatic trial with two arms to assess the effectiveness of 38% SDF and 5% NaF in preventing new caries lesions in primary anterior teeth. Methods: 688 three-year-old kindergarten children who are healthy will be recruited, stratified by school, and block randomized to receive either 38% SDF (treatment group) or 5% NaF (standard treatment group) therapy on primary upper anterior teeth. This sample size is sufficient for a superiority trial with power at 90%, allowing for a 15% dropout rate. The primary outcome is the number of sound tooth surfaces that become cavitated caries per child at 12-month follow-up. The secondary outcome is the number of carious tooth surfaces developed after baseline that become arrested at 12-month for each child. Dental examinations for the status of caries (active or arrested) will be conducted by the same calibrated examiner. The examiner, children and children's parents will be blind to treatment allocation. Parents will be surveyed to study the children's oral health-related behaviours and socioeconomic backgrounds, which will allow the adjustment for effect modification. Possible results and implications: If the results are as anticipated, it will help change the standard of care for caries prevention. If adopted in Hong Kong, SDF therapy will prevent 20,800 (13% of the 160,000) kindergarten children from having caries developed in their anterior teeth, thus reduce significantly the burden of ECC of the children and related stress of their family. Moreover, the results will be widely available and increase adoption of SDF in other countries to reduce the global burden of ECC among children.

Inclusion Criteria:

• generally healthy, with parental consents

Exclusion Criteria:

• uncooperative and difficult to manage, have major systemic diseases such as porphyria, or are on long-term medication such as anti-epileptic drugs.