Objective. Diagnosis of secondary caries with the DIAGNOdent device has been found to be comparable to visual and radiographic diagnostic methods, but the fluorescence of restorative materials might affect DIAGNOdent values and result in false-positive diagnosis. The aims of this study were: (1) to measure baseline fluorescence of restorative materials and fluorescence changes induced by aging, bleaching, staining, and polishing; (2) to assess intra-examiner reproducibility of these measurements; and (3) to compare the values obtained with the DIAGNOdent against the threshold values for enamel and dentinal caries. Material and Methods. 270 disk-shaped specimens fabricated from 15 different restorative materials were divided into 3 groups, which were aged in water, bleached with 10% carbamide peroxide, and stained with red wine. Specimen fluorescence was measured with the DIAGNOdent before and after these treatments. The red-wine-stained specimens were also polished and measured again. Results. Intra-examiner reproducibility of the measurements was excellent. For all materials, baseline DIAGNOdent values, as well as the values of aged and bleached samples, were considerably lower than the dentinal caries threshold. The values of one stained filled resin fissure sealant, one stained resin composite, and one stained resin-modified glass ionomer exceeded the dentinal caries threshold. Polishing reduced these DIAGNOdent values to below the dentinal caries threshold, except for the filled resin fissure sealant specimen. Conclusions. Stained dental materials might affect DIAGNOdent readings and consequently result in false-positive diagnoses of secondary caries. Dental fillings should be polished prior to DIAGNOdent measurement.