title: Evaluation of the Effect of Needle Position on Irrigant Flow in the C-shaped Root Canal Using a Computational Fluid Dynamics Model.
abstract: BACKGROUND
  The purpose of this study was to investigate the effect of the orientation of a side-vented needle on the irrigant flow pattern in a C-shaped root canal system using computational fluid dynamics and to evaluate the real-time replacement of irrigant in the lateral canal (LC).
  
  
  METHODS
  A mandibular second molar with a complete C-shaped canal system was chosen for this study. The root canals were prepared and scanned, and then the images were exported to design software. A 30-G, side-vented irrigation needle was positioned with the open notch facing the lateral canal (case A) and rotated 90°, 180°, and 270° clockwise (cases B, C, and D, respectively). The flow pattern, irrigant replacement, velocity distribution, wall stress distribution, and apical pressure in the canal were analyzed.
  
  
  RESULTS
  Most of the irrigant flowed to the canal outlet from the adjacent instrumented canal space with different trajectories in the 4 cases. The concentration of scalar immediately below the tip of the needle was exchanged quickly; the length of the cleared zone extended 3 mm beyond the tip of the needles. The depth of circulation in the LC in all cases increased during the first 0.2 seconds. After that, the exchange of irrigant reached a stable phase. Irrigant penetration in the LC was greatest in cases A and B (<1.1 mm). Apical pressure in case B was significantly lower than in other groups.
  
  
  CONCLUSIONS
  The scalar concentration can be used to evaluate the replacement of irrigant in the root canal over time. Orientation of the opening of the side-vented needle influences the flow pattern, velocity, apical wall pressure, and penetration into the LC.
authors: State Key Laboratory of Oral Diseases, West China College and Hospital of Stomatology, Sichuan University, Chengdu, China.
authors: Ruyan
authors: R
authors: Wang
authors: Division of Endodontics, Department of Oral Biological and Medical Sciences, Faculty of Dentistry, University of British Columbia, Vancouver, Canada.
authors: Ya
authors: Y
authors: Shen
authors: Department of Stomatology, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China.
authors: Jingzhi
authors: J
authors: Ma
authors: State Key Laboratory of Oral Diseases, West China College and Hospital of Stomatology, Sichuan University, Chengdu, China.
authors: Dingming
authors: D
authors: Huang
authors: State Key Laboratory of Oral Diseases, West China College and Hospital of Stomatology, Sichuan University, Chengdu, China.
authors: Xuedong
authors: X
authors: Zhou
authors: State Key Laboratory of Oral Diseases, West China College and Hospital of Stomatology, Sichuan University, Chengdu, China. Electronic address: gaoyuan@scu.edu.cn.
authors: Yuan
authors: Y
authors: Gao
authors: Division of Endodontics, Department of Oral Biological and Medical Sciences, Faculty of Dentistry, University of British Columbia, Vancouver, Canada.
authors: Markus
authors: M
authors: Haapasalo
mesh_terms: D019295:Computational Biology; D006801:Humans; D057446:Hydrodynamics; D007091:Image Processing, Computer-Assisted; D008963:Molar / Q000000981:diagnostic imaging; D009339:Needles; D012388:Root Canal Irrigants / Q000008:administration & dosage*; D018915:Root Canal Preparation / Q000379:methods*; D013314:Stress, Mechanical; D055114:X-Ray Microtomography
chemical_list: D012388:Root Canal Irrigants
keywords: C-shaped root canal; computational fluid dynamics; lateral canal; real time; side-vented needle