Comparative Fluorescence Spectroscopy Shows Differences in Noncavitated Enamel Lesions

Abstract

The aim of this study was to compare emission spectra from noncavitated enamel caries with different degrees of discoloration under a wide range of excitation wavelengths. Freshly extracted human molars with white spot, light discolored and dark discolored brown spot enamel caries were selected (n = 4 each). Rectangular blocks (3.5 × 3.5 mm) were cut from the carious area and a corresponding sound area of the same tooth. Emission spectra were recorded from carious and the corresponding sound areas using a fluorescence spectrophotometer at excitation wavelengths from 360 nm up to 580 nm in steps of 20 nm. The specimens were submerged in water during measurement. The spectra were corrected and normalized to peak intensity for comparisons between spectra from sound and carious areas of each tooth. Excitation spectra were recorded for selected emission wavelengths that showed maximum intensity. Emission spectra of all types of carious lesions were shifted towards longer wavelengths (red shift) when compared to the spectra of the corresponding sound enamel. The red shift was highest for dark brown spot lesions and lowest for white spot lesions (p ≤ 0.001). Distinct fluorescence bands within 600–700 nm typical for porphyrin compounds were strongest for excitation wavelengths from 400 to 420 nm and present in most of the lesions investigated.