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Intracanal Vaporized Bubble Kinetics and Apical Pressure During Root Canal Irrigation Activated by Er:YAG laser:

: Objective: This study aimed to analyze the eﬀect of tip conﬁguration and length of irradiation time on intracanal vaporized bubble kinetics and apical pressure during laser-activated root canal irrigation（LAI） with Er:YAG laser. Materials and methods: A plastic pipette tip was modiﬁed as a simulated root canal model（apical diameter 0.40 mm, 6% ta-per, 20 mm long）. The canal model was ﬁlled with distilled water and LAI was performed using an Er:YAG laser unit（Erwin AdvErl, J. Morita, Kyoto） with a ﬂat-ended tip（C600F） or a cone-shaped tip（R600T） at 70 mJ, 10 pps. The end of the laser tip was ﬁxed at 15 mm from the root apex. Kinetics of vapor bubbles in the simulated root canal during the lasing were moni-tored with a high-speed camera, and the bubble count and velocity at 100, 500 and 1000 milliseconds were analyzed with video analysis software. The maximum pressure generated outside the apical foramen during 5 seconds of laser irradiation was measured with a pressure sensor connected to the apex of the root canal model. Results: As for the vapor bubble count, there was no signiﬁcant main eﬀect of tip conﬁguration（ｐ＞0.05）, whereas the main eﬀect of irradiation time was signiﬁcant（ｐ＜0.05）. The number of vapor bubbles showed a signiﬁcant increase with increasing the irradiation time（ｐ＜0.05）. Regarding the vapor bubble velocity, there was no signiﬁcant main eﬀect of either tip conﬁguration or time（ｐ＞0.05）. There was no signiﬁcant diﬀerence between the two types of laser tips with regard to the apical pressure. Conclusion: In LAI with an Er:YAG laser, the tip conﬁguration did not aﬀect the intracanal bubble count, velocity or apical pressure, whereas the increase of irradiation time signiﬁcantly increased the bubble count.