title: Visualization of irrigant flow and cavitation induced by Er:YAG laser within a root canal model.
abstract: BACKGROUND
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Endodontology and Operative Dentistry, Division of Oral Rehabilitation, Faculty of Dental Science, Kyushu University, Fukuoka, Japan. himeka30@dent.kyushu-u.ac.jp
authors.forename: Himeka
authors.initials: H
authors.lastname: Matsumoto
authors.forename: Yoshito
authors.initials: Y
authors.lastname: Yoshimine
authors.forename: Akifumi
authors.initials: A
authors.lastname: Akamine
mesh_terms: D003786:Dental Pulp Cavity / Q000033:anatomy & histology*; D006801:Humans; D057446:Hydrodynamics; D053844:Lasers, Solid-State / Q000627:therapeutic use*; D045423:Microbubbles; D010781:Photography; D012212:Rheology; D012388:Root Canal Irrigants / Q000008:administration & dosage* / Q000737:chemistry; D007507:Therapeutic Irrigation / Q000379:methods; D013997:Time Factors; D014835:Volatilization; D014867:Water / Q000737:chemistry
chemical_list: D012388:Root Canal Irrigants; D014867:Water