:A Preliminary Study
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概要
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In our previous paper, it was reported that metal dowel cores could be removed by pulsed Nd: YAG laser irradiation. The purpose of this study was to investigate the effects of pulsed Nd: YAG laser irradiation on the periodontal tissue during removal of a dowel core cemented in the middle of the root canal <I>in vitro</I>.<BR>Fourteen extracted single-rooted human teeth were used in the first experiment. After removing the tooth crown, they were randomly divided into two groups, no cooling group and water cooling group. In both groups, root canals were cleaned, shaped and obturated. Then, a post space 7.5mm in length was created, and a dowel core 3 mm in length was fixed with glass ionomer cement in each tooth. The dowel cores were made from an Au-Ag-Pa alloy.<BR>Nd: YAG laser (output energy: 900 mJ 5 pps) irradiation through an optical fiber (∅=400μm) was performed with or without water cooling to remove the dowel cores from the root canal. The temperature elevation on the root surfaces was evaluated by thermography.<BR>In the second experiment, eighteen extracted single-rooted human teeth were used and randomly divided into two groups, 5°C and 10°C temperature elevation groups. In both groups, a modified water cooling system was introduced during lasing. Nd: YAG laser irradiation was carried out as in the first experiment, and the change of temperature on the root surfaces was evaluated.<BR>The results were as follows:<BR>1. In the no cooling group and water cooling group, the time for 5°C temperature increase was 4.64 (±0.47) and 11.8 (±4.24) sec, respectively. There was a statistically significant difference (unpaired t-tset, P<0.05) between the two groups.<BR>2. In the 5°C and 10°C temperature elevation groups, the time needed for temperature increase was 9.61 (±2.37) and 31.8 (±17.5) sec, respectively.<BR>From the results, it was suggested that continuous irradiation of pulsed Nd: YAG laser within 30sec could produce little thermal effect on the surrounding tissues.
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