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ePaper created 2018-03-14, 11:21:34 | version 1.38.0
| research Nd:YAG laser-assisted removal of instrument fragments Dr Georgi Tomov, Bulgaria The Nd:YAG lasers tested in laboratory studies have been claimed to be able to successfully manage the re- moval of instrument fragments within root canals1–4. This is done in four ways, all correlated to temperature effects: 1. Laser melts the dentine around the fragment and then Hedstrom files are used to bypass and retrieve the fragment. 2. Laser melts the entire fragment. 3. Laser energy melts the solder, connecting the fractured instrument with a brass tube charged with solder and placed at the exposed coronal end of the fragment. 4. Laser welds the file fragment positioned within a metal hollow tube (e.g. Endo-Eze® Tip, Ultradent Products; Figs. 1a & b). laser irradiation.1 Yu et al. found that the temperature rose by 17 °C to 27 °C, but argued that, since the initial tem- perature was lower than human body temperature, these results were irrelevant.2 The findings demonstrated that a pulsed Nd:YAG laser irradiation has the capability of removing broken files. The success rate reported by Yu et al. was 55 per cent.2 How- ever, the thermal effects found after Nd:YAG irradiation in dry root canals were considerable (Figs. 2a–c). Thus, the focus now is on the outcomes of using a laser fibre in- serted into a hollow tube (alone or in the presence of sol- der) both to avoid dentinal carbonisation and to achieve welding between the separated file and metal tube. The removal of a claimed minimum amount of root den- tine1, 2, 4 can be attributed to the potential given to the user of Nd:YAG laser to distinguish dentine1 from obstructions by the difference in acoustics produced by the two ma- terials. Ebihara et al. observed that some orifices of the dentinal tubules were blocked with melted dentine after Intraoral laser welding The intraoral laser welding phenomenon is well re- searched.1–4 Even for metals that absorb well, such as steel, the laser light is initially reflected. A small percentage of the laser light is absorbed, heating the metal surface. Fig. 2b Fig. 1a Fig. 1b Fig. 2a Fig. 2c Figs. 1a & b: Welding of separated K-type file in Endo-Eze® Tip (18 gauge) using Nd:YAG laser irradiation at 400 mJ and 10 Hz (a). Longitudinally cross-sec- tioned metal tubes with melted K-type files inside (b). Figs. 2a–c: Undesirable thermal effects of Nd:YAG irradiation (3 W, 300 mJ, 10 Hz) in a dry root canal (a). When the optic fibre comes into contact with the dentinal wall it can cause carbonisation and melting. SEM image of a control dentinal surface (b) and dentine irradiated with an Nd:YAG laser, revealing areas of melting and dentinal tubule closure (c). 06 1 2018