Fluoride uptake by human tooth enamel: Topical application versus combined dielectrophoresis and AC electroosmosis

Purpose: To compare fluoride uptake by enamel after applying 1.23% acidulated phosphate fluoride gel to human tooth enamel topically (n=12) or with combined dielectrophoresis and AC electroosmosis (DEP/ACE) at frequencies of 10,400 and 5,000 Hz (n=12) for 20 minutes. Methods: DEP/ACE induced nonuniform electrical fields with three alternating current frequencies to polarize, orient, and motivate fluoride particles. Fluoride concentrations were measured at various enamel depths using wavelength dispersive spectrometry. Data were analyzed by ANOVA/Student-Newman-Keuls post hoc tests (P <= 0.05). Results: Fluoride concentrations in the diffusion group were significantly higher than baseline readings at 10, 20 and 50 mu m depths. Fluoride concentrations in DEP/ACE-treated teeth were significantly higher than the diffusion group at 10, 20, 50, 100, 200 and 300 mu m (ANOVA/Student-Newman-Keuls post hoc, P < 0.05). Fluoride uptake with DEP/ACE was substantially higher than diffusion at 10, 20, 50, 100, 200 and 300 mu m depths (paired t test, P < 0.05). DEP/ACE transported fluoride up to 300 mu m deep, whereas conventional fluoride application was comparatively ineffective beyond 20 mu m depth (P < 0.05). Compared to passive diffusion, fluoride uptake in enamel was significantly higher in the DEP/ACE group at 10, 20, 50, 100, 200 and 300 mu m depths (P < 0.05). DEP/ACE drove fluoride substantially deeper into human enamel with a difference in uptake 1,575 ppm higher than diffusion at 100 mu m depth; 6 times higher at 50 mu m depth; 5 times higher at 20 mu m depth; and 7 times higher at 10 mu m depth. Fluoride levels at 100 mu m were equivalent to long-term prophylactic exposure.