Monitoring acid-demineralization of human dentine by electrochemical impedance spectroscopy (EIS)

Objective The purpose of this study was to monitor in situ acid-induced demineralization of dentine by using electrochemical impedance spectroscopy (EIS) and correlate the EIS findings with changes in the chemical composition and ultrastructure of dentine. Method EIS was used to monitor the process of demineralization of dentine induced by an acid model. Scanning electron microscopy (SEM) was used to examine the ultrastructure, while energy dispersive X-ray (EDX) and X-ray diffraction (XRD) analysis were employed to investigate the changes in the chemical composition of surface dentine with demineralization. Results Two kinds of equivalent circuits that matched the histological structure of dentine were used to fit the EIS data. The parameters Rd, which is the resistance of the bulk of dentine layer and Rct, which is the charge transfer associated with the penetration of electrolyte into the dentinal tubules, decreased with increasing duration of demineralization. SEM images showed that the smear layer on the dentine and peritubular dentine disappeared with demineralization. The EDX results showed that the content of calcium and phosphorus decreased consistently with the decreasing content of HAP as shown by the XRD results. The findings from this study suggested that the changes in Rd and Rct determined by the EIS corresponded well with the variation in structure and composition of dentine. Conclusions EIS could be employed to monitor structural and chemical compositional changes induced by acid-demineralization on dentine surface.