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The aim of this study was to compare fluorescence emission spectra from carious root dentin under a wide range of excitation wavelengths. Freshly extracted human molars with single intact root caries lesions were selected. The carious area thereof was either dark discoloured (n = 3) or light discoloured (n = 5). A rectangular block (3.5 x 3.5 mm) was cut from each carious area and a corresponding sound area of the same root, leaving the outer surface intact. Emission spectra were recorded from the carious and corresponding sound areas using a fluorescence spectrophotometer at excitation wavelengths from 360 to 580 nm in steps of 20 nm. The specimens were submerged in water during the measurements. The emission spectra were corrected and normalized to peak intensity for comparisons between spectra from sound and carious areas of each root. Distinct fluorescence bands around 623 and 688 nm, typical for porphyrin compounds, were strongest for excitation wavelengths around 400-420 nm and present in five of the lesions investigated. All lesions showed red shift at half maximum when compared to sound root dentin at all excitation wavelengths. Dark discoloured lesions showed stronger red-shift at lower excitation wavelengths as compared to light discoloured lesions. It is concluded, that root caries lesions reveal distinct fluorescence emission typical for exogenous porphyrin compounds which may provide means for diagnostic procedures. Supported by Grant BU 1203/2-1 from the Deutsche Forschungsgemeinschaft |