Objectives: The aim of this investigation was to determine the influence of a variety of parameters on the effectiveness of hard substance ablation and the thermal side effects when using Er:YAG laser (Key I and 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 250-400 mJ/pulse, 3-15 pps and 20-180 s processing time, and in the 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 volumetrically 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 ANOVA (Bonferroni). Also a liner regression analysis was done using Pearson's coefficient.
Results: The results show that with the Er:YAG laser, in combination with water-spray cooling, an effective 3D ablation rate (up to 0.017 mm3/pulse = 50 microns 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 conditioning of the dentin surface and, in the case of conditioning with black ink, a low ablation rate (0.00004 mm3/pulse = linear 0.2 micron/pulse) was found.
Significance: In contrast to the Er:YAG laser, it is apparent, 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 reason, the use of the Nd:YAG laser at higher total energies is not recommended. The temperature rise with the Nd:YAG laser is dependent on the direction of the dentin tubuli. Dentin tubuli running parallel to the 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-propagating theory for spreading effects of laser beams in dentin.