Effect of Fluoride Varnish on Enamel Microhardness: An in vitro Study

Remineralization counteracts demineralization, which is the loss of mineral ions from dental enamel, by restoring the mineral. Remineralization itself could be enhanced by external factors such as fluoride contained in fluoride varnish. This study aimed to determine the difference in enamel microhardness before and after applying 5% sodium fluoride (NaF) fluoride varnish.

This experimental laboratory in vitro study used 40 premolar crowns as samples. All samples were demineralized in a pH 4 demineralizing solution for 6 hours. The samples were split into two groups, each containing 20 samples. Group I (Control) acted as a control and Group II (Fluoride Varnish) was treated with 5% NaF (fluoride varnish). Then all samples were immersed in artificial saliva for seven days. A Vickers microhardness tester measured the samples' pre-demineralization, post-demineralization, and post-remineralization microhardness. The dependent sample t-test analysis was used to determine the difference in microhardness in each group. The two sample t-test analysis was used to determine the difference in microhardness between groups.

The findings indicated that fluoride varnish application increases the demineralized enamel microhardness in Group II (Fluoride Varnish) from 174.63 VHN (SD = 23.12; 95% CI: 163.81-185.44) to 270.58 VHN (SD = 26.52; 95% CI: 258.17-282.99) (p-value = 0.000). The increase in Group II (Fluoride Varnish) was higher than in Group I (Control) after remineralization of seven days (p-value = 0.002).

The findings show a significant increase in enamel microhardness following fluoride varnish application, measured on the seventh day (p-value 0.000). This demonstrates the effectiveness of fluoride varnish in increasing enamel hardness under these in vitro experimental conditions. This study can serve as a reference for clinicians selecting fluoride varnish as a caries prevention effort.