The effect of pulsed CO<sub>2</sub>-laser treatments on the microstructure and nanomechanical properties was studied
using atomic force microscopy and nanoindentation. The microstructure and roughness of dentin
specimens treated by a 9.3 μm CO<sub>2</sub> laser at fluences of 0.5; 0.75; 1.0; and 1.5 J/cm<sup>2</sup> were evaluated and the
elastic modulus and hardness before and after a nine days demin/remin application for laser treatments at
0.75 and 1.5 J/cm<sup>2</sup> were determined. The hypothesis that CO<sub>2</sub>-laser-treatments reduce or inhibit the
demineralization process was tested. Surface cracks were observed at fluences of 0.75 J/cm<sup>2</sup> and higher.
Surface roughness increased strongly after laser irradiation and was about 10 times higher at maximum
fluence. Mechanical properties profiles from the laser treated surface to sound dentin showed increased
modulus and hardness values at dentin surfaces treated, indicating removal of organic phases and
reinforcement of the tissue by increased mineral content. Mechanical properties decreased after
demin/remin application in all groups and the hardened surface layer disappeared for samples treated at
0.75 J/cm<sup>2</sup>. While increased properties were still observed in the laser affected surface zone for treatments
at 1.5 J/cm<sup>2</sup>, demineralization was severe underneath these layers as indicated by a sharp drop in properties.
The depth of demineralization was slightly decreased in the laser-treated group compared to the untreated
controls. We conclude that CO<sub>2</sub>-laser treatments produce dentin surfaces with increased nanomechanical
properties. These surface layers do not, however, provide protection against demineralization due to surface
cracking and possible delamination. Moreover, the surface cracks induced by the laser-irradiation raise
concerns about a clinical potential for caries inhibition in dentin.