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The applicability of laser induced fluorescence for early caries diagnosis was tested. The influence of laser radiation wavelength on emission characteristics of sound and demineralized enamel was examined using various fiber spectrum analysers and systems for fluorescence imaging. Samples of healthy enamel, carious enamel, and enamel demineralized in vitro were ground and pressed to form flat, uniform samples. Different laser light sources emitting wavelengths of 442, 532 and 633 nm were used to induce fluorescence in the samples. The spectra of fluorescence were registered and fluorescence images were captured with a CCD camera and then analyzed. Results showed the intensity of fluorescence of enamel decalcified in vitro to be lower than that of healthy enamel, regardless of the wavelength of excitation light. In the case of carious enamel, changes were found to depend on the wavelength of excitation light. When excited by wavelengths of 442 nm (green light) and 532 nm (blue light), the fluorescence intensity of carious enamel was found to be lower than that of sound enamel. When excited by wavelengths of 633 nm (red light) the fluorescence intensity of carious enamel was found to be greatly higher than that of sound enamel. Concluding, the difference in fluorescence intensity between sound and carious enamel may justify the use of this phenomenon in early caries diagnosis. However, fluorescence intensity registered in enamel samples depends on several factors: the wavelength of excitation light, character of demineralization (in vivo or in vitro), and the structure of the fiber optic sensor used for measurement. Deeper penetration of dental tissue obtained by red light suggests that this may be the appropriate source to use for more advanced carious lesions. The systems equipped with blue light sources are more effective in early caries diagnosis.
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