Application of Er: YAG laser to retrograde cavity preparation
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概要
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The purpose of this <I>in vitro</I> study was to determine if Er: YAG laser was capable of preparing retrograde cavities. The root canals of 40 extracted single-rooted human teeth were prepared to size 45 apically and obturated with laterally condensed gutta percha and sealer. Root ends were resected at 90 degrees 3mm from the apex. Then, the roots were randomly divided into two groups.<BR>Retrograde cavities were prepared with Er: YAG laser (output energy: 70mJ10pps) or an ultrasonic retro tip. Working time was counted and the rate of increase in the root canal area at the resected surface measured, and they were statistically analyzed. In addition, retrograde cavity surfaces were evaluated with scanning electron microscopy. On the other hand, retrograde cavities of 7 roots in each group were filled with EBA cement. The root surfaces were sealed with nail polish and all samples were placed into 0.1% methylene blue dye for 3 days. Finally, they were split and the dye penetration length was measured and statistically analyzed.<BR>The results were as follows:<BR>1. Working time of the Er: YAG laser group and ultrasonic group was 52 (±27) and 176 (±62) sec., respectively. Er: YAG laser could prepare the retrograde cavity significantly quicker than ultrasonics. (Mann-Whitney U-test, <I>P</I><0.0001)<BR>2. The rate of postoperative increase in the roof canal area of the Er: YAG laser group and ultrasonic group was 212 (±72) and 198 (±58) %, respectively. There was no significant difference between the two groups (<I>t</I>-test, <I>P</I>=0.338).<BR>3. There were no debris, gutta percha or sealer left on the retrograde cavity surface prepared by Er: YAG laser. The shape of the retrograde cavity was spread and irregular at the resected surface. On the other hand, debris and sealer were observed at cavity surfaces cut by ultrasonics and the cavity was cylindrical in shape.<BR>4. Dye penetration length from the resected surface in the Er: YAG laser group and ultrasonic group was 1.01 (±0.18) and 1.30 (±10.61) mm, respectively. There was no significant difference between the two groups. (<I>t</I>-test, <I>P</I>=0.253)
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