3D volume-ablation rate and thermal side effects with the Er:YAG and Nd:YAG laser.
OBJECTIVE
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.


CONCLUSIONS
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.
Mehl
A
A
Department of Operative Dentistry, School of Dentistry, Munich, Germany. amehl@dent.med.uni-muenchen.de
Kremers
L
L
Salzmann
K
K
Hickel
R
R
D000538:Aluminum Silicates; D000704:Analysis of Variance; D001831:Body Temperature; D003737:Dental Cavity Preparation / Q000295:instrumentation / Q000379:methods*; D003743:Dental Enamel / Q000601:surgery; D003782:Dental Pulp / Q000503:physiopathology; D003804:Dentin / Q000503:physiopathology / Q000601:surgery* / Q000648:ultrastructure; D004871:Erbium; D006358:Hot Temperature; D006801:Humans; D007281:Ink; D053685:Laser Therapy / Q000295:instrumentation / Q000379:methods*; D007834:Lasers; D009354:Neodymium; D012044:Regression Analysis; D013223:Statistics as Topic; D013499:Surface Properties; D013821:Thermometers; D013997:Time Factors; D019228:Tooth Crown / Q000601:surgery; D014867:Water; D015019:Yttrium
D000538:Aluminum Silicates; D014867:Water; D009354:Neodymium; D015019:Yttrium; D004871:Erbium