[Holmium:YAG infrared laser and UV-Excimer. Laser effects on oral mucosa]

The in-vivo tissue ablation characteristics of a pulsed infrared laser (Holmium:YAG, lambda = 1980) and a pulsed excimer laser (XeCl, lambda = 308 nm) were studied. The holmium laser energy was coupled into nylon fibres. The excimer laser energy was coupled into quartz fibers. Laser incisions were made on white rats at different sites of the tongue. Power settings of 400 mJ per 2.5 microseconds pulse at 5 pulses per second for the holmium:YAG laser and 250 mJ per 1 microsecond pulse at 20 pulses per second for the excimer laser were used. Thermal gradients following laser application were measured. Excellent control of depth of tissue ablation was noted for both types of lasers. The tissue response was examined by light microscopy. Histological studies revealed tissue defects with clean contours. The coagulative necrosis zone for the 400 mJ holmium:YAG injuries measured from 370 microns to 640 microns, compared with 40 microns to 160 microns with the 250 mJ UV-excimer injuries. Wound healing was studied over a six-week period. Histologically, wound closure was completed after four weeks showing re-epithelialization without scar formation for both types of laser. The in-vivo tissue ablation characteristics and the operation reliability of the two lasers were compared.