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laser - international magazine of laser dentistry No. 1, 2018

Fig. 3 research | Fig. 3: SEM image of a K-type file after Nd:YAG laser irradiation at 400 mJ and 10 Hz revealing a melted metal surface with an irregular granular structure after solidification. The increased surface temperature increases the absorp- tion of the laser power. This creates a snowball effect, in which the material is rapidly heated by the laser, leading to melting and the consequent formation of a weld. odontic instruments were removed successfully in 17 out of 22 cases (77.3 per cent) in which more than 1.5 mm was tangible. When less than 1.5 mm was tangible, the removal success rate decreased to three out of 11 cases (27.3 per cent). Hagiwara et al. performed laser welding on stainless steel or nickel-titanium files using an Nd:YAG laser in order to evaluate the retention force between the files and the metal extractor.3 Additionally, they evaluated the increase in temperature on the root surface during laser irradiation. They reported that the retention force on stainless steel was significantly greater than that on nickel- titanium. The maximum temperature increase was 4.1 °C. The temperature increase on the root surface was greater in the vicinity of the welded area than at the api- cal area. Scanning electron microscopy (SEM) revealed that the files and extractors were welded together. Similar results were found by Tomov (unpublished data; Fig. 3). In vitro study Cvikl et al. used a brass tube charged with solder and placed at the coronal end of the fractured instrument in their in vitro experiment.4 Nd:YAG laser energy was used to melt the solder, connecting the fractured instrument with the brass tube. They reported that the fractured end- Kurz & bündig These results obtained from in vitro experiments indi- cate that the laser welding method is effective in remov- ing broken instruments from root ca- nals, but its efficacy has to be further verified in clinical trials. Literature All figures: © Georgi Tomov, 2016 contact Dr Georgi T. Tomov DDS, MS, PhD Associate Professor and Head of the Department of Oral Pathology Faculty of Dental Medicine Medical University of Plovdiv Bulgaria dr.g.tomov@gmail.com Author details Im Zuge von Laborstudien wurden Nd:YAG-Laser bereits erfolgreich, mit dem Ziel Instrumentenfragmente aus Wurzelkanälen zu ent- fernen, genutzt. Dies kann auf vier verschiedene Arten erfolgen, jeweils korrelierend mit temperaturinduzierten Effekten. Der Autor betont, dass in früheren Studien von geschmolzenem Dentin verschlossene Dentintubuli festzustellen waren, welche durch die Nd:YAG-Laser- bestrahlung verursacht wurden. Die thermalen Effekte erwiesen sich besonders bei trockenen Wurzelkanälen als erheblich. Um diese Dentinkarbonisierung und -schmelze zu vermeiden, legt sich der Fokus nun verstärkt auf Laserschweißen, d. h. das Fragment wird (meist mithilfe von Lötmetall) innerhalb einer Messingröhre unter Verwendung von Lichtleitfasern gebunden und entfernt. Im Ergebnis von In-vitro-Experimenten erwies sich diese Methode des Laserschweißens als effektiv im Entfernen abgebrochener endodontischer Instrumente aus Wurzelkanälen. Ihre Effizienz gilt es, in klinischen Versuchen weiter zu belegen. 1 2018 07

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