Improved mineralization of dental enamel by electrokinetic delivery of F- and Ca2+ ions

Abstract

This in vitro study evaluated the effects of the infiltration of F^- and Ca²⁺ ions into human enamel by electrokinetic flow (EKF) on the enamel microhardness and F^- content. Sound human enamel ground sections of unerupted third molars were infiltrated with de-ionized water by EKF and with F^- ion by EKF respectively. All samples were submitted to two successive transverse acid-etch biopsies (etching times of 30 s and 20 min) to quantify F^- ion infiltrated deep into enamel. Remarkably, sound enamel showed a large increase in microhardness (MH) after infiltration of NaF (p < 0.00001) and CaCl₂ (p = 0.013) by EKF. Additionally, NaF-EKF increased the remineralization in the lesion body of artificial enamel caries lesions compared to controls (p < 0.01). With the enamel biopsy technique, at both etching times, more F^- ions were found in the EKF-treated group than the control group (p << 0.05), and more fluoride was extracted from deeper biopsies in the NaF-EKF group. In conclusion, our results show that EKF treatment is superior in transporting Ca²⁺ and F^- ions into sound enamel when compared to molecular diffusion, enhancing both the mineralization of sound enamel and the remineralization of artificial enamel caries.

Figure 1

Agreement (Bland & Altman) plot of the difference in microhardness (in HV values) (EXP–CTRL) against their mean average (experimental & control) for (a) the CaCl₂ group and (b) the NaF group. Short-dash red line represents equality; Solid purple line represents the Mean difference in hardness; Dotted orange lines represent 95% CI limit; Black dash lines represent the limits of agreement (LOA) with 95% CI. In (a) one outlier positive value was found, while in (b) two outlier negative values were found.

Figure 2

Preparation of specimen and experimental design. (a), (b) The tooth sample is die-cut into thin sections, which include the whole tooth crown. (c), (d) Each ground sheet is removed from part of its dentine and extracted from the buccal and lingual surfaces of the mid-crown region. (e), (f) Each enamel ground section is glued on a standard glass slide. The ground section sample is then measured for baseline MH at varying distances from the original enamel surface. (g) Subsequently, set it up in the microfluidic chip for specific EKF treatment. (h) Post-MH test is then performed on the treated sample section. (i) Lastly, the sample was submitted for Fluoride ion concentration measurement (in μg F/cm²).