Quantitative light-induced fluorescence as a potential tool for detection of enamel chemical composition

Background: Little is known about how the chemical composition of enamel affects the optical properties of teeth, but advances in technology allow this to be studied using white-light and fluorescent images. This study aimed to identify the variation in enamel chemical composition that may affect tooth optical properties, such as tooth color and autofluorescence. Methods: Sixty-one specimens of extracted human molars were prepared. Raman spectrometry was used to assess chemical composition of enamel, and tooth color, and autofluorescence from enamel were evaluated by quantitative light-induced fluorescence (QLF) images. Pearson correlation and multiple linear regression analyses were used. Results: Enamel fluorescence was related to enamel composition rather than tooth color. The b* value from the fluorescence image had a moderate correlation with crystallinity (full-width at half-maximum: r = −0.433, p < 0.001) and laser-induced fluorescence intensity (r = 0.450, p < 0.001) from Raman spectroscopy. In multiple linear regression analysis, the chemical composition of the tooth had a significant effect on the b* value from the fluorescent image (R² = 0.433, p < 0.001). In contrast, tooth color values (L*, a*, and b*) were not correlated with chemical composition. Conclusions: The present study revealed that enamel autofluorescence in QLF was related to chemical composition of the enamel, particularly the inorganic‒organic interface. While enamel chemical composition can be detected only in a laboratory environment, enamel fluorescence by QLF may enable estimation in a dental clinic, which has implications for the field of tooth bleaching or esthetic restorative materials.