Effects of Nd:YAG laser on the permeability of root canal wall dentin

The effects of a thermally cooled pulsed Nd:YAG laser on the permeability and structural appearance of the root canal wall were investigated in vitro. Twenty specimens of freshly extracted human teeth were prepared by conventional methods. The teeth were randomly divided into two groups. Group 1 teeth were prepared conventionally but not lased. Group 2 specimens received three 15-s laser exposures totaling 45 s duration within the root canal via optical fiber delivery. Laser parameters were set at 5 W, 50 Hz, using a simultaneous air/water coolant spray of 10 psi air and 2 psi water. The external surfaces of the teeth were sealed with acrylic and placed in 2% methylene blue dye for 24 h. The teeth were then sectioned, photographed, and compared under light microscope for the extent of dye penetration. The specimens were subsequently prepared for scanning electron microscopy for correlation of permeability measurements with surface modifications. The combined use of scanning electron microscopy and dye permeability measurements revealed a sealing of the dentinal wall by deposition of glass-like material and, in one specimen, the bridging of a lateral canal that partially occluded the canal. Based on statistical comparisons, permeability of laser-treated teeth was significantly less than untreated specimens (alpha = 0.005).