Autofluorescence Loss in Photobleaching for Human Dentin ex vivo

Two-photon fluorescence microscopy was performed on the enamel-dentin junction area of a humantooth using a femtosecond pulsed laser. We obtained a clear image contrast between the bright dentinand dark tubules with the autofluorescence generated from the endogenous fluorophores in dentin. Theautofluorescence shows a broad spectrum due to complex cross links between dentinal collagens, whichextend from blue to orange wavelengths (470–590 nm), but a gradual autofluorescence loss in pho-tobleaching was observed for a long-term exposure under strong excitation. For increasing excitationpower, we found that two-step decay becomes significant in the spectrally integrated autofluorescence.