Study On Preparation And Formation Mechanism Of Hydroxyapatite Coatings On Human Enamel By Electrochemical Technique

The early stage of caries was the effective stage for preventing and treating the caries. In this study, an electrochemical system was founded. Electrichemical technique was adopted to prepare hydroxyapatite coatings on human enamel that had artificial initial enamel lesions. The hydroxyapatite coatings could tightly combine to the enamel surfaces and exhibited a strong resemblance to the sound human enamel in Vickers micro-hardness. Also, the antibacterial activities of the enamel surfaces were improved. Then the initial enamel lesions were prevented and restored rapidly and effectively.Effects of process prameters (such as the initial pH value of electrolyte, concentration of calcium and phosphorus species, temperature of the system, time, current density, etc.) on morphology, compositon and physicalchemical character of hydroxyapatite coatings were analyzed synthetically in this study. Thermodynamic calculations were carried out, and a model that was corresponding to the formation of hydroxyapatite coatings on enamel surface by electrochemical technique was proposed. Then the kinetic equations governed by the diffusion process were presented and confirmed by the relative studies that were carried out. Eventually, the possible mechanism was proposed based on the thermodynamic and kinetic analysis.The results showed that the degree of caries could be judged effectively using electrochemical impedance spectroscopy techniques. After acid treatment, initial enamel lesions could be gained and the hydrophilicity of the samples was improved. These were helpful for the preparation of coatings. In addition, the preferential (002) orientation showed a similar value in the comparison between the sound enamel and hydroxyapatite coatings that were prepared with the current density of 0.5mA/cm~2 at 328K when the initial pH value was 6. The dimension of hydroxyapatite crystal decrease significantly upon the increasing temperature and the decreasing concentrations of calcium and phosphorus species, then the surface became smooth. It was indicated that the growth rate of hydroxyapatite coating was mainly controlled by the diffusion of ions towards to the cathode. An induction period was exised during the hydroxyapatite precipitation, which showed a decrease upon increasing temperature. Two important steps, hydrogen evolution reaction and formation of hydroxyapatite precipitation, were contained in the formations of the hydroxyapatite coatings on human enamel surface by electrochemical tschnique.In conclusion, it was a novel method to restore the initial enamel lesions by preparing hydroxyapatite coatings on human enamel using electrochemical technique. And it was significant to prevent and restore the initial enamel lesions rapidly and effectively in clinic.