LAUSR

INTRODUCTION Retrieving a separated file in the root canal system requires a skilled clinician. A metal file can be removed by ablation via the Nd:YAP laser, however the efficiency and potential hazards of the ablation procedure are still unclear. The aim of this study was twofold: to investigate the efficiency of file ablation using the Nd:YAP laser and to evaluate the rise in temperature of the root surface in vitro. METHODS Part 1: #10, #15 C-files and ProTaper Next X1, X2 files were selected. Under 8.5 magnification, the Nd:YAP laser was used to ablate the files starting at D0. The length of the file was recorded after each 5-pulse ablation. Part 2: Three files each, #15 C-file and ProTaper Next X2 were separated in 6 distal roots of mandibular second molars with single canals. 2-pulse and 5-pulse modes were used to ablate the separated files and the rise in root surface temperature was recorded with an infrared camera. Another 3 unaltered distal roots served as the negative control. Scanning electron microscope (SEM) evaluation: The teeth were split with bone scissors and observed under SEM the to evaluate the surface change of the file and the root canal wall. RESULTS 1): The average length of the ablated files after each 5-pulse interval was 0.113-0.158mm, with no statistical difference between different files. 2) The temperature rise of the negative control group (mean±SD: 1.86±0.11°C; 5.81±0.35°C for 2 and 5-pulse group) was significantly lower than the roots with separated files (mean±SD: 3.74±0.20°C, 4.02±0.11°C for 2-pulse C-file and ProTaper Next X2; 8.47±0.19°C, 9.04±0.20°C for 5-pulse C-file and ProTaper Next X2). The temperature rise of all groups was lower than 10°C. The 2-pulse group showed a lower temperature rise than the 5-pulse group. The diameter or the type of alloy had no effect on the temperature rise. CONCLUSION Separated files (stainless steel or Ni-Ti alloy) can be ablated by the Nd:YAP laser. When the number of pulses is less than 5, the temperature rise of the root surface is considered safe to the surrounding periodontium.