Combination of Cold Helium Plasma with Fluoride Varnish to Improve Enamel Surface Protection

This study aimed to determine the optimal application sequence of cold atmospheric helium plasma (CAP) with fluoride varnish to enhance enamel protection and fluoride uptake. A total of 91 bovine incisor teeth were randomly assigned into seven groups (<i>n</i> = 13 each): negative control (C, no treatment), comparative controls [helium gas (He, gas only)], helium plasma (P, plasma only)], positive control [fluoride varnish (V)], and three experimental groups: plasma followed by varnish (PV), varnish followed by plasma (VP), and plasma before and after varnish (PVP). Specimens were analyzed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX), and microhardness testing at 0, 24, and 48 h post-treatment. SEM revealed that helium plasma treatment enhanced the even dispersion of fluoride and reduced imperfections on the enamel surface. EDX analysis indicated significant alterations in the elemental composition, particularly with respect to the amount of fluoride (F) and the calcium-to-phosphorus (Ca/P) ratios. In the PVP group (CAP before and after varnish), the fluoride atomic percentage increased notably from 1.21% (varnish group) to 7.31% at 48h. Concurrently, the Ca/P ratio increased from 1.95 to 2.39 corresponding with a statistically significant 24% improvement in enamel hardness (repeated-measures ANOVA with Bonferroni correction, <i>p</i> < 0.05). The timing of CAP application critically affects fluoride absorption and enamel hardening. This study clearly demonstrates how sequential CAP treatment maximizes fluoride effectiveness, offering a promising route for non-invasive caries prevention.