It was hypothesized that resin infiltration in conjunction with fluoride varnish treatment of smooth-surface caries lesions in deciduous teeth reduce considerably the progression of treated caries lesions, compared to fluoride varnish therapy only.

• 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.
• Participants were allocated to the "test" and to the "control" group, respectively, by computer-generated randomly permuted blocks using package blockrand in R statistical software, sealed in envelopes.
• The children were re-examined clinically by the same 2 examiners as at baseline evaluation.
• Statistical analyses were performed using statistical software STATISTICA 10 (StatSoft), the level of significance was set at 0.05. Intra-examiner reliability was assessed by kappa statistics.
• To compare average values between two independent groups U Mann-Whitney test was used (for e.g. to compare experimental group with the control one); Wilcoxon signed-rank test was used for paired samples (for e.g. to compare first measurement with final measurement for experimental group). Comparison of fractions was conducted using Pearson's chi-square test of independence and Z test. The 95% confidence intervals were calculated on the basis of normal approximation.

Inclusion Criteria:

• at least two active smooth-surface caries lesions in deciduous teeth (ICDAS II code 2)
• a written consent of parents/ guardians for participation in the research study

Exclusion Criteria:

• age above 5.9 years
• systematic disease
• cavitated lesions
• enamel defects
• current participation in another study
• a planned change of residence within one year