Purpose of the study is to evaluate the effectiveness of Fluor Protector S in preventing tooth decay in adolescents and to isolate factors that reduce its effectiveness.

In this study, half of the randomly assigned participants will received fluoride varnish (Fluor Protector S) and will be considered an intervention group. The other half will undergo placebo application.

Evidence from 6 systematic reviews involving 200 trials and more than 80,000 participants further supports the effectiveness of fluoride varnishes, applied professionally 2-4 times a year, for preventing dental caries. Additionally, the simultaneous use of fluoride varnishes with fluoride toothpaste appears to significantly enhance the caries-inhibiting effect compared with the use of fluoride toothpaste alone. The relative benefit of fluoride varnishes application seems to occur irrespective of baseline caries risk, baseline caries severity, background exposure to fluorides and application features such as prior prophylaxis, concentration of fluoride or frequency of application.

To determine the sample size, the results of epidemiological studies conducted in the framework of the health monitoring of the Polish population in 2015 in the group of people aged 15 years (dmf = 5.75) and in 2016 in the group of people aged 12 years (dmf = 3) 0.7 as annual growth of caries, and literature data on the effectiveness of fluoride varnish in the prevention of permanent tooth decay in the general population at 43% (a reduction of about 0.3% per year in dmf, Standard Deviation = 0.8) and was considered achievable in the case Apply Fluor Protector S at 3 months intervals in the high risk group of caries. Size of the study group with such assumptions (α = 0,05, power = 80%, mean reduction of dmf: 0,3, Standard Deviation = 0,8 ; t test for comparison of two groups) - Minimum 84 patients [70 patients+ 20% (dropped out), in both groups].

Participants will be allocated to the "test" and to the "control" group, respectively, by computer-generated randomly permuted blocks using R package in statistical software..

• The children will be examined and re-examined clinically by the same examiners.
• Statistical analyses will be performed using statistical software, 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 will be used (for e.g. to compare experimental group with the control one); Wilcoxon signed-rank test will be used for paired samples (for e.g. to compare first measurement with final measurement for experimental group). Comparison of fractions will be conducted using Pearson's chi-square test of independence and Z test. The 95% confidence intervals will be calculated on the basis of normal approximation.

Purpose of the study is to evaluate the effectiveness of Fluor Protector S in preventing tooth decay in adolescents and to isolate factors that reduce its effectiveness.

Inclusion Criteria:

• Age> 12 ≤ 19 years
• All permanent teeth (except the third molar teeth)
• Restored caries lesions
• Teeth with International Caries Detection and Assessment System II score 0, 1, or 2
• Agreement of parents / legal guardians and patients to participate in the study

Exclusion Criteria:

• Planned change of residence during the year
• Chronic illness or medication that increases the risk of tooth decay
• Orthodontic treatment
• Caries lesions

All participants,Care Providers, Investigators and Outcomes Assessor will be aware of the current subject's allocation and will be unconscious which product is fluoride varnish and which placebo. participants assigned to intervention(s) based on a protocol Patients will be distributed between Group A (Fluor Protector S) and group B (placebo) according to allocation for 2 types of intervention and blindness (codes for the type of intervention A and B will be assigned to patient numbers according to the reporting order and placed in opaque envelopes).