3D VOLUME-ABLATION RATE AND THERMAL SIDE-EFFECTS WITH THE ER-YAG AND ND-YAG LASER

Objectives. The aim of this investigation was to determine the influen ce of a variety of parameters on the effectiveness of hard substance a blation and the thermal side effects when using Er:YAG laser (Key I an d II, KaVo) and Nd:YAG laser (SunLase 800, Sunrise Technologies/Orbis) . Methods. For this study, ablation and temperature measurements were carried out on 170 dentin slices and 170 extracted teeth via computer- controlled cavity preparation. The Er:YAG laser settings varied from 2 50 - 400 mJ/pulse, 3 -15 pps and 20 - 180 s processing time, and in th e case of the Nd:YAG laser from 83 - 100 mJ/pulse, 10 - 20 pps, and 20 - 260 s processing time. The ablation rate was measured volumetricall y via a 3D sensor. Temperatures were measured for each setting both on the dentin slice and in the pulp of the extracted teeth. The results were analyzed using a t-test for independent samples and a one-way ANO VA (Bonferroni). Also a liner regression analysis was done using Pears on's coefficient. Results. The results show that with the Er:YAG laser , in combination with water-spray cooling, an effective 3D ablation ra te (up to 0.017 mm(3)/ pulse = 50 mu m linear) can be achieved without raising the temperature of the surrounding tissue. In the case of the Nd:YAG laser, no measurable ablation rate was evident without conditi oning of the dentin surface and, in the case of conditioning with blac k ink, a low ablation rate (0.00004 mm(3)/pulse = linear 0.2 mu m/puls e) was found. Significance. In contrast to the Er:YAG laser, it is app arent, that with the Nd:YAG laser from a total energy of 80 J onwards, the rise in temperature in the pulp is above 8 degrees C. For that re ason, the use of the Nd:YAG laser at higher total energies is not reco mmended. The temperature rise with the Nd:YAG laser is dependent on th e direction of the dentin tubuli. Dentin tubuli running parallel to th e surface prevent significant heat penetration, whereas those running in a transverse direction to the surface (= parallel to the laser beam ) support the penetration of heat. This finding supports the light-pro pagating theory for spreading effects of laser beams in dentin.