This study evaluated the effects of a sodium fluoride-chitosan (NaF/Chit) gel without a crosslinker on Streptococcus mutans biofilm, enamel demineralization, and cell viability. The synthesized 5.6% NaF/Chit gel was characterized by rheological tests (steady and oscillatory shear tests and viscosity), Electrical Impedance Spectroscopy (EIS) to measure impedance modulus, real and imaginary components, admittance, and ion dissociation and Fourier Transform Infrared Spectroscopy (FTIR). Enamel blocks were prepared and assigned to five groups (n = 5): 2.8% Chit, 2.8% NaF, 5.6% NaF/Chit, 1.23% commercial acidulated phosphate fluoride (APF) (positive control), and acetic acid (negative control). S. mutans biofilm were grown for 48 h with daily 1-min applications of each group. The colony-forming units (CFU/mL) and the change in the surface Knoop hardness percentage (%KHN) were assessed before and after biofilm growth. Cytotoxicity was tested using RAW 264.7 cells (MTT assay). The 5.6% NaF/Chit gel showed a rigid and thixotropic profile and higher viscosity than the 2.8% Chit gel. EIS confirmed the ion release of Na+ and F- ions from the 5.6% NaF/Chit gel. The 5.6% NaF/Chit, 2.8% Chit, and 2.8% APF groups significantly reduced S. mutans CFU/mL compared with the control groups. The 5.6% NaF/Chit was able to significantly reduce enamel %KHN after biofilm exposure (8.3% KHN) compared to other groups. The 5.6% NaF/Chit IC50 was 0.086 mg/mL. The 5.6% NaF/Chit gel demonstrated favorable physicochemical characteristics and effective biological activity, significantly reducing S. mutans biofilm and enamel demineralization with low cytotoxicity. The 5.6% NaF/Chit suggests promising clinical potential as a cariostatic biomaterial.
Reis et al. (2026) studied this question.