In vitro demineralization of human enamel natural and abraded surfaces: A micromechanical and SEM investigation

Objectives

To compare the demineralization pattern that occurs in abraded samples and unabraded ones quantitatively and microscopically using nanoindentation and SEM.

Methods

Using 12 human third molars, one half of each tooth was abraded to a depth approximately 200 μm below the outer surface enamel, and the other half was left untreated. All specimens were demineralized for 3 d, 5 d, 7 d and 14 d respectively. The cross sections of all lesions were evaluated with nanoindentation and SEM.

Results

Unabraded samples had least loss of mechanical properties and lesion depth compared to abraded samples, with most mechanical property loss occurring within a shallower layer of the lesion. The variation of mechanical properties in unabraded samples was wider than abraded samples. SEM images showed a characteristic “keyhole” structure for both samples after demineralization, with the rod core extensively demineralized while the interrod remained intact. Acid attack initiated at the rod sheath space then penetrated into the rod core before extending into neighbouring rods through the rod tail.

Conclusion

Abraded samples exposed to in vitro demineralization form deeper lesion depths and greater loss of mechanical properties than unabraded samples subjected to the same demineralization. Unabraded samples manifested characteristic subsurface demineralization with a shallow surface layer that remained intact, whereas no intact surface was found in abraded samples. The demineralization pattern of unabraded samples more closely resembled the pattern of natural white spot lesions and displayed wide inter-sample variation. Consideration should be given to experimental design with unabraded teeth specimens for future demineralization studies.