Identification of the physical modification threshold of dentin induced by neodymium and holmium YAG lasers using scanning electron microscopy.

Laser application to dentin has been advocated to modify the dentin substrate for restorative procedures. We examined the minimum energy density required to physically modify the dentin surface using 1.06 microns and 1.32 microns Neodymium:Yttrium-Aluminum-Garnet (Nd:YAG) and 2.10 microns Holmium-YAG (Ho:YAG) lasers. Three millimeter thick dentin sections from the middle occlusal third of crowns of third molars were used. To determine the effect of surface preparation, the sections were ground to 240, 320, 400, 600 grit or polished to 0.5 micron. Smear layer was removed using 0.5 M EDTA for 2 minutes. Five single pulse repetitions at each laser parameter were performed. Power (W) and energy per pulse (mJ/p) were increased for each wavelength until a physical modification occurred. The energy density (J/cm2) was then held constant and the threshold was confirmed using 200, 320 and 550 microns diameter quartz contact probes. Scanning electron microscopy (SEM) was used to verify the physical modification of the dentin. The physical threshold remained constant for ground and polished surfaces. Similar surface modifications were found for the three wavelengths tested. The threshold modifications occurred at 207, 165, and 83 J/cm2 for the 1.06 microns, 1.32 microns and 2.10 microns lasers, respectively. For all emission wavelengths tested the physical threshold modification occurred at relatively low energy densities. These lasers show promise for surface modification of dentin.