This observational cohort study aims to evaluate the short-term (3 months) efficacy of the standard fluoride therapy in the German National Health System for managing hypersensitive carious lesions in primary teeth (fluoride varnish application), and further compare it to a different fluoride therapy utilizing a silver-containing fluoride agent combined with potassium iodide solution.

A single trained investigator will screen for possible study participants of children aged 2-5 years old, and their parents will be asked to participate in the study. The participants will be consecutively recruited from regular clinic attendees of the Department of Preventive and Pediatric Dentistry at the University of Greifswald, from whom present with active carious lesions (ICDAS 5) along symptoms of hypersensitivity to be treated with fluoride varnish, and further compared to participants treated with silver fluoride and potassium iodide application.

Eligibility to the study will be determined by a single trained examiner through clinical findings of caries activity according to Bjørndal criteria, and reported history of hypersensitivity symptoms obtained from the parent/caregiver of the participant, followed by hypersensitivity confirmatory test using a triple syringe air blast on the exposed surface of the carious lesion to allocate areas with suspected dentin hypersensitivity.

After clinical examination and obtainment of an informed consent, eligible children will be treated with fluoride varnish application (Duraphat®), or silver fluoride and potassium iodide application (Riva Star®) according to manufacturer's instructions.The participant's behavior shall be evaluated at the beginning, during and after treatment. Plaque Index (API) and Papillary Bleeding Index (PBI) will also be assessed prior to treatment and at the 3-months mark. Procedures will be performed by six different dentists (four pediatric specialists and two post-graduate pediatric dentistry students), all of whom were briefed on the study protocol and received instructions in carrying in the interventions according to the manufacturer's guide, and their technical opinions regarding the performed procedures will be obtained following the procedure. Follow up examinations after 3 months will be done by a single examiner. Only one tooth per child will be included in the analysis.

Data and information of this study will be recorded, handled, and stored in an organized and secure way, to allow its accurate reporting, interpretation, and verification. To assure confidentiality of clinical records, an unambiguous subject identification code will be used. Patients who are no longer willing to continue in the study will have the right to quit at any time without any penalty.

All variables will be statistically analyzed using descriptive statistics, plots, and tests of normality. Means and standard deviations (SD) will be calculated for all quantitative variables, while frequencies and percentages will be calculated for categorical variables.

Comparison between the two study groups will utilize independent samples t-test for quantitative normally distributed variables, and Mann-Whitney U for quantitative non-normally distributed variables and qualitative ordinal variables. Chi-squared and Fisher exact tests will be performed for comparing qualitative nominal variables between the two study groups. Comparing the baseline and follow-up shall be done using paired t-test when the variable is normally distributed, and Wilcoxon signed rank test when the variable is not normally distributed. For comparing lesion activity before and after treatment, McNemar test will be used and Friedman test for comparing the children's behavior at 3 different time points (before, during and after treatment).

A Significance will be set at p<0.05. Data will be analyzed using IBM SPSS statistical software for windows (version 25).

Inclusion Criteria:

• Reported hypersensitivity in primary teeth associated with the presence of active carious lesions (ICDAS 5).
• Healthy children aged 2-5 years.
• Not using any desensitizer for 1-month prior the study.
• Willing to be examined.

Exclusion Criteria:

• Previously restored teeth.
• Teeth with signs or symptoms of irreversible pulpitis.
• Patients with any systemic disease requiring special considerations during their dental treatment.
• Parents/children who declined to participate in the study.