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The mechanical and optical properties of healthy and transparent root dentin are compared using atomic force microscopy (AFM), micro-Raman and emission spectroscopies and fluorescence microscopy. The elastic modulus and hardness of intertubular and peritubular transparent and healthy dentin did not differ appreciably. The tubule filling material in the transparent zone, however, exhibited values between peritubular and intertubular dentin. Raman spectroscopy revealed a shift in the 1066 cm−1 band to 1072 cm−1 from normal to transparent intertubular dentin. The material filling the tubule lumen in transparent dentin showed an increase in frequency of the band near 1070 cm−1 as well. The emission spectral characteristics under 351 nm photoexcitation indicate differences between normal and transparent intertubular dentin. A transition region of about 300 μm between normal and transparent dentin was identified. In this region the intertubular emission properties were the same as for normal dentin, but tubules were filled. The filling material had emission characteristics closer to the normal intertubular than to transparent intertubular dentin. © 2001 Kluwer Academic Publishers