Influence of cold plasma activation on fluoride uptake and demineralization of enamel

This in vitro study investigated the influence of cold plasma activation time prior to 1.25% fluoride gel application on fluoride uptake and demineralization of enamel.

Human enamel specimens (n = 200) were either treated with a dielectric-barrier plasma discharge at a constant distance (d = 1 mm), pulse repetition frequency (f₁ = 1 kHz), power (P_mean=36 mW) and voltage (U_pp=28 kV) for 0.5, 1, 2, or 30 s or received no plasma activation (each n = 40). Subsequently, half of the specimens from each group were coated with fluoride gel (1.25% NaF/AmF, t = 5 min). In each group, one subset of specimens (n = 10) was treated with KOH (1 M, 24 h) to quantify surface-deposited fluoride. Remaining specimens (n = 10) were demineralized (citric acid, pH 2.3, 60 s) to determine structurally bound fluoride as well as calcium and phosphate release. Statistical analysis was performed using linear mixed models and generalized linear mixed models with Tukey post-hoc tests (p < 0.05).

Fluoride gel significantly increased KOH-soluble and structurally bound fluoride and reduced calcium and phosphate release. Cold plasma activation had no significant effect on fluoride uptake or calcium and phosphate release. Plasma activation for 2 and 30 s resulted in a significant reduction of the calcium/phosphate ratio compared to the groups without plasma activation and without fluoride gel (p_adj.<0.001).

Single cold plasma activation prior to fluoride gel application did not improve fluoride uptake or reduce demineralization of enamel.

Under the investigated conditions, additional cold plasma activation provided no benefit beyond conventional topical fluoride treatment.