An In Vitro Comparative Study of Intracanal Fluid Motion and Wall Shear Stress Induced by Ultrasonic and Polymer Rotary Finishing Files in a Simulated Root Canal Model
Objective. This in vitro study compared the flow pattern and shear stress of an irrigant induced by ultrasonic and polymer rotary finishing file activation in an acrylic root canal model. Flow visualization analysis was performed using an acrylic canal filled with a mixture of distilled water and rheoscopic fluid. The ultrasonic and polymer rotary finishing file were separately tested in the canal and activated in a static position and in a cyclical axial motion (up and down). Particle movement in the fluid was captured using a high-speed digital camera and DaVis 7.1 software. The fluid shear stress analysis was performed using hot film anemometry. A hot-wire was placed in an acrylic root canal and the canal was filled with distilled water. The ultrasonic and polymer rotary finishing files were separately tested in a static position and in a cyclical axial motion. Positive needle irrigation was also tested separately for fluid shear stress. The induced wall shear stress was measured using LabVIEW 8.0 software. 1. Introduction No matter which endodontic rotary nickel-titanium (NiTi) file system a clinician chooses to incorporate into their conventional endodontic treatment in conjunction with sodium hypochlorite (NaOCl) and ethylenediaminetetraacetic acid (EDTA) irrigation, there will always be some canal debris left on the dentinal walls [1]. An in vitro study by Chuste-Guillot et al. [2] demonstrated, regardless of the NiTi rotary file system used as a root canal preparation technique in the experiment, the root dentin remained infected and was not bacteria-free. There are several main reasons as to why there is residual canal debris after conventional endodontic treatment instrumentation and irrigation. First, nickel-titanium files stay centered in the canal and thus will not contact walls that have various invaginations or irregularities. Second, canal morphology can be complex making it difficult for the chemical-mechanical canal preparation to be effective in removing all the debris. Current concepts in conventional endodontics recommend the use of lubricating and chelating agents during the cleaning and shaping phase. Also, it has been recommended to use copious irrigation of NaOCl during all phases of instrumentation along with the removal of the smear layer prior to obturation [3]. With apical leakage of bacteria or bacteria toxins from a root canal system being one of the main causes of the prevention of periradicular healing, eliminating as much canal wall debris (smear layer) as possible is important [4]. A study by Ricucci et al. [5]
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