Monitoring bacterial-demineralization of human dentine by electrochemical impedance spectroscopy.
OBJECTIVE
The purpose of this study was two-fold: (1) to monitor bacterial biofilm formation and bacteria-induced demineralization of dentine in situ by using electrochemical impedance spectrum (EIS); (2) to examine the relationship between EIS findings and changes in the chemical composition and ultrastructure of dentine during bacteria-induced demineralization.


METHODS
In this study, dentine demineralization was induced by Streptococcusmutans (ATCC 25175) in the presence of sucrose in culture medium and was monitored using two EIS measurement systems (Type A with a working electrode and Type B without a working electrode). Scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) and X-ray diffraction (XRD) were employed to examine the morphology, element contents and crystallinity of hydroxyapatite (HAP) on the dentine surface. Transverse microradiography (TMR) was used to characterize the lesion depth and degree of mineral loss during demineralization.


RESULTS
The resistance of the bulk dentine (R(d)) and the apparent resistance of dentine (R(a)) measured from the Type A and Type B EIS systems, respectively, decreased gradually with demineralization. The resistance of the biofilm formed on dentine surface was determined by fitting the EIS data with equivalent circuits. The presence of biofilm slightly increased R(a) of dentine before demineralization. However, the electrochemical behavior of biofilm did not affect the decreasing impedance of dentine with demineralization. The SEM, EDX, XRD and TMR results demonstrated that the surface and bulk dentine gradually became more porous due to the loss of minerals during demineralization, which in turn resulted in the decrease in R(d) and R(a) values obtained from EIS systems.


CONCLUSIONS
This investigation highlighted EIS as a potential technique to monitor biofilm formation and bacterial-induced demineralization in situ.
Department of Restorative Dentistry, Faculty of Dentistry, National University of Singapore, 5 Lower Kent Ridge Road, 119074 Singapore, Singapore.
Zhang
Z
Xu
Koon Gee
KG
Neoh
Bennett
B
Amaechi
Anil
A
Kishen
D018441:Biofilms; D002327:Cariostatic Agents / Q000008:administration & dosage; D003461:Crystallography; D003470:Culture Media; D003804:Dentin / Q000737:chemistry / Q000382:microbiology* / Q000648:ultrastructure; D017886:Durapatite / Q000032:analysis / Q000737:chemistry; D017097:Electric Impedance; D055664:Electrochemical Techniques / Q000295:instrumentation; D004566:Electrodes; D006801:Humans; D008852:Microradiography / Q000379:methods; D008855:Microscopy, Electron, Scanning; D008903:Minerals / Q000032:analysis / Q000737:chemistry; D016062:Porosity; D016369:Smear Layer; D013052:Spectrometry, X-Ray Emission; D013057:Spectrum Analysis / Q000379:methods*; D013295:Streptococcus mutans / Q000502:physiology*; D013395:Sucrose / Q000008:administration & dosage; D013997:Time Factors; D017001:Tooth Demineralization / Q000382:microbiology* / Q000473:pathology; D014961:X-Ray Diffraction
D002327:Cariostatic Agents; D003470:Culture Media; D008903:Minerals; D013395:Sucrose; D017886:Durapatite