Department of Endodontology and Operative Dentistry, Division of Oral Rehabilitation, Faculty of Dental Science, Kyushu University, Fukuoka, Japan.
J Endod. 2011 Jun;37(6):839-43. doi: 10.1016/j.joen.2011.02.035. Epub 2011 Apr 17.
Laser-activated irrigation (LAI) has recently been introduced as an innovative method for root canal irrigation. However, there is limited information about the cleaning mechanism of an Er:YAG laser. In this study, we visualized the action of laser-induced bubbles and fluid flow in vitro to better understand the physical mechanisms underlying LAI.
An Er:YAG laser was equipped with a novel cone-shaped tip with a lateral emission rate of approximately 80%. Laser light was emitted at a pulse energy of 30, 50, or 70 mJ (output energy: 11, 18, or 26 mJ) and a repetition rate of 1 or 20 pulses per second, without air or water spray. Fluid flow dynamics in a root canal model were observed by using glass-bead tracers under a high-speed camera. Moreover, laser-induced bubble patterns were visualized in both free water and the root canal model.
Tracers revealed high-speed motion of the fluid. A full cycle of expansion and implosion of vapor and secondary cavitation bubbles were clearly observed. In free water, the vapor bubble expanded for 220 microseconds, and its shape resembled that of an apple. In the root canal model, the vapor bubble expanded in a vertical direction along the canal wall, and bubble expansion continued for ≥700 microseconds. Furthermore, cavitation bubbles were created much more frequently in the canal model than in free water.
These results suggest that the cleaning mechanism of an Er:YAG laser within the root canal might depend on rapid fluid motion caused by expansion and implosion of laser-induced bubbles.
激光激活冲洗（LAI）最近被引入作为根管冲洗的一种创新方法。然而，关于 Er:YAG 激光的清洗机制的信息有限。在这项研究中，我们通过体外实验可视化了激光诱导气泡和流体流动的作用，以更好地理解 LAI 的物理机制。
配备了一个具有大约 80%侧向发射率的新型锥形尖端的 Er:YAG 激光。激光在 30、50 或 70 mJ 的脉冲能量（输出能量：11、18 或 26 mJ）和 1 或 20 脉冲/秒的重复率下发射，没有空气或水喷雾。在高速摄像机下，使用玻璃珠示踪剂观察根管模型中的流体流动动力学。此外，在自由水和根管模型中可视化了激光诱导气泡模式。
示踪剂显示出高速的流体运动。清晰观察到蒸汽和二次空化气泡的膨胀和内爆的完整循环。在自由水中，蒸汽泡膨胀了 220 微秒，其形状类似于苹果。在根管模型中，蒸汽泡沿着管壁垂直方向膨胀，气泡膨胀持续时间≥700 微秒。此外，在根管模型中产生的空化气泡比在自由水中频繁得多。
这些结果表明，根管内 Er:YAG 激光的清洗机制可能取决于激光诱导气泡膨胀和内爆引起的快速流体运动。
