- To determine the number of patients, sample size was based on data from studies assessing fluoride varnish efficacy in children with deciduous teeth (progression of caries reduction by 33 %)(95% CI, from 19 to 48%, P<0.0001); (α = 0.05; power = 80%; chi-square test2). The calculated sample size was 60 children and 120 white spot lesions. The initially planned number of participants was increased by expected 20% drop-out after 1 year, at least 72 children; the minimal number of treated active caries lesions amounted to 144.