Sample size calculations: Based on the assumption that 80% of the treated teeth do not get caries and that 10% difference in caries development constitutes a clinically meaningful difference, it is required to recruit 180 participants in the study for the split-mouth design. Considering a potential maximum of annual 20% drop-out rate and a 3-years follow-up, the study will need to recruit 400 participants in order to have at least 206 children at the 3 years of follow-up.