Acoustic streaming induced by an ultrasonically oscillating endodontic file

Area of Science:

• Biomedical Engineering
• Fluid Dynamics
• Dental Research

Background:

• Ultrasonically activated irrigation (UAI) is an advanced endodontic technique.
• Its cleaning efficacy relies on acoustic streaming, which generates pressure and shear stresses within the root canal.
• Understanding these hydrodynamic forces is crucial for optimizing UAI.

Purpose of the Study:

• To investigate acoustic streaming, pressure, and shear stress induced by ultrasonically oscillating endodontic files.
• To compare the contributions of oscillatory and steady flow components.
• To analyze the impact of root canal confinement on these hydrodynamic effects.

Main Methods:

• Utilized a combination of theoretical analysis, numerical predictions, and experimental validation.
• Employed high-speed particle tracking velocimetry for experimental measurements.
• Investigated fluid dynamics in a two-dimensional root canal cross-section.

Main Results:

• Acoustic streaming theory accurately describes the flow induced by oscillating files.
• The oscillatory flow component is dominant, generating significantly higher pressure and shear stress than the steady component.
• Root canal confinement enhances oscillatory velocities and associated stresses, while affecting steady jet formation.

Conclusions:

• The oscillatory component of acoustic streaming is critical for UAI's effectiveness.
• Previous studies underestimating oscillatory flow may have underestimated UAI's hydrodynamic impact.
• Accurate modeling of UAI requires considering both oscillatory and steady flow dynamics, especially within confined root canal geometries.