Method: Dentin demineralization was induced by incubating dentin specimens with Streptococcus mutants (ATCC 25175) in the presence of sucrose. Two EIS-systems (with a working electrode (Type-A) and without a working electrode (Type-B)) were used to monitor demineralization-induced changes in dentin. Scanning-electron-microscopy (SEM), field-emission-scanning-electron-microscopy (FE-SEM), Energy-dispersive-X-ray (EDX) and X-ray-diffraction (XRD) were employed to examine the physico-chemical characteristics of the hydroxyapatite on the surface dentin. Transverse-microradiography (TMR) was used to characterize the lesion-depth and degree of mineral-loss during demineralization.
Results: With 14-day demineralization, in Type-A EIS-system the resistance of the bulk dentin (Rd) decreased from 97.21±17.78 to 9.28±2.12 kohm (p<0.005) and the resistance of biofilm reached 571±68 ohm. In Type-B EIS-system the apparent resistance of dentin (Ra) decreased from 1.88±0.08 to 0.62±0.05 kohm (p<0.005) in the presence of sucrose, while the biofilm formed on dentin caused Ra to increase from 1.99±0.13 to 2.19±0.12 kohm (p<0.005) in the absence of sucrose. The SEM, EDX, XRD and TMR results demonstrated that the surface and bulk-dentin gradually became more porous due to the loss of minerals during demineralization, which in turn resulted in the decrease in Rd and Ra values.
Conclusions: EIS-technique can be a convenient and reliable method to monitor biofilm formation and demineralization induced substrate changes in dentin in vitro. It also has a prospective potential to estimate the effect of remineralization and treatment for tooth hypersensitivity.
(This study was finically supported by the funding from the Office of Life Science (cross faculty grant) (NUS) R-224-000-031-123 and the Academic Research Funding (NUS) R-224-000-029-112.)