Some composite resins contain luminophorous agents in order to reproduce tooth fluorescence. The objective of this study was to compare the fluorescence spectra emitted by composite resins with those of human enamel and dentin, and their emission behaviour after a 90-day natural aging period. Nine shades of the composite resins Z350XT/3M (XT), Opallis/FGM (OP) and Empress Direct/Ivoclar-Vivadent (ED) were analyzed. Five specimens (10.0 mm x 2.0mm) were fabricated for each shade. Enamel (5.0 mm x 0.30 mm) and dentin (5.0 mm x 1.0 mm) specimens were obtained from sound human third molars. Fluorescence spectra of human dentin and enamel as well as the composite specimens immediately after fabrication were measured at the excitation peaks of 375, 395 and 410 nm. To assess composite resin fluorescence intensity changes over time, measurements were conducted after 30, 60 and 90 days, at 395 nm. Differences in fluorescence intensity over time were analyzed with ANOVA and Tukey?s test (p<0.05). Fluorescence spectra baseline values of composites demonstrated no differences in intensity among the excitation peaks tested, with maximum emission found at the peak of 450 nm. Enamel and dentin spectra varied with different excitations, and the greater the excitation, the longer the wavelength in comparison to composite resins. After 90 days, XT presented an increase in fluorescence intensity, while OP and ED showed a reduction when compared with baseline values. Fluorescence intensity of composite resins changed during the period analyzed, with an emission behavior different from that of human enamel and dentin. The main changes occurred in the first 30 days.