Purpose: This laboratory study examined the ablative processes in human radicular dentine using the Ho:YAG laser (2100 nm wavelength, pulse duration 250-350 μs, spot size 320 μm). Materials and Methods: The study followed a matrix design, with pulse energies from 0.5 to 1.6 J and pulse frequencies from 1 to 6 Hz, in either the presence or absence of water mist spray (1.5 ml/min). Dentine surfaces of extracted teeth were lased with collateral water mist spray or without irrigation. Diameters and depths of impact craters were measured, and the nature of the lased surface was assessed using light microscopy and SEM. Results: When used with collateral water mist spray, the ablation craters had smooth outlines indicative of an entirely explosive process without adjacent collateral damage. In contrast, in the absence of water spray, peripheral carbonization and vitrification zones were seen. There was a significant correlation between the depth and diameter of the craters and the applied energy of the laser pulse. Conclusions: These laboratory findings suggest that when used with collateral water spray, the Ho:YAG laser can ablate human dentine in a controlled manner without adverse thermal effects. Because it can be delivered through glass optical fibers, this wavelength may have application for dental hard tissue preparation or modification.

Keywords: laser dentistry, holmium lasers, dentine ablation, SEM evaluation