FT-Raman Spectroscopy Study of the Remineralization of Microwave-Exposed Artificial Caries

Dental caries is a microbially mediated disease that can result in significant tooth structure degradation. Although the preponderance of lesions is treated by surgical intervention, various strategies have been developed for its noninvasive management. Here, we use a novel approach for noninvasive treatment based on killing Streptococcus mutans with high-frequency microwave energy (ME). The rationale for this approach is based on modulating the pH of caries to a physiological state to enable spontaneous tooth remineralization from exogenous sources. In the present study, after demonstrating that ME kills > 99% of S. mutans in planktonic cultures, 8 enamel slabs were harvested from a single tooth. Baseline mineral concentration at each of 12 points per slab was obtained using Fourier transform (FT)-Raman spectroscopy. Surface demineralization was subsequently promoted by subjecting all samples to an S. mutans acidic biofilm for 6 d. Half of the samples were then exposed to high-frequency ME, and the other half were used as controls. All samples were next subjected to a remineralization protocol consisting of two 45-min exposures per 24-h period in tryptic soy broth followed by immersion in a remineralizing solution for the remaining period. After 10 d, samples were removed and cleaned. FT-Raman spectra were again obtained at the same 12 points per sample, and the mineral concentration was determined. The effect of the remineralization protocol on the demineralized slabs was expressed as a percentage of mineral loss or gain relative to baseline. The mineral concentration of the microwave-exposed group collectively approached 100% of baseline values, while that of the control group was in the order of 40%. Differences between groups were significant (P = 0.001, Mann-Whitney U test). We concluded that killing of S. mutans by ME promotes effective remineralization of S. mutans-demineralized enamel compared with controls.