Cavitation in a periodontal pocket by an ultrasonic dental scaler: A numerical investigation.

Periodontal pockets are spaces or holes surrounded by teeth under the gum line. These pockets can become filled with infection-causing bacteria resulting in tissue, bone, and tooth loss. Cavitation produced by the oscillating tip of dental ultrasonic scalers plays a significant role in routine periodontal therapy to clean these areas. Numerical studies were conducted for a scaler vibrating in a periodontal pocket which was simplified to a hole, using ABAQUS based on the finite element method. The simulations consider the three-dimensional, nonlinear, and transient interaction between the vibration and deformation of the scaler tip, the water flow around the scaler and the cavitation formation. The numerical model was validated by comparing results with experimental data for a scaler vibrating in an unbounded liquid, the displacement at the free end of the scaler and the cavitation pattern near the scaler tip displaying excellent agreement. A parametric study for a scaler vibrating in a hole has been carried out in terms of the volume of the hole, the taper ratio (the radius ratio between the circular opening and bottom of the hole), and the immersion depth of the scaler tip in the hole. The amount of cavitation generated is evaluated by the cavitation density (or the void fraction) which is the ratio of the volume of the cavitation occupied in the hole to the total volume of the hole. Numerical results indicate that the cavitation density in the hole increases with the decreasing hole volume and the increasing taper ratio. It is inferred that cleaning effects could be increased if some modifications to the scaler design could be made to increase the blocking effect of the hole during the cleaning process. Cavitation is observed in the hole even if the scaler is placed above the hole and increases with the immersion depth.

Imaging and Quantification of the Area of Fast-Moving Microbubbles Using a High-Speed Camera and Image Analysis.

An experimental and image analysis technique is presented for imaging cavitation bubbles and calculating their area. The high-speed imaging experimental technique and image analysis protocol presented here can also be applied for imaging microscopic bubbles in other fields of research; therefore, it has a wide range of applications. We apply this to image cavitation around dental ultrasonic scalers. It is important to image cavitation to characterize it and to understand how it can be exploited for various applications. Cavitation occurring around dental ultrasonic scalers can be used as a novel method of dental plaque removal, which would be more effective and cause less damage than current periodontal therapy techniques. We present a method for imaging the cavitation bubble clouds occurring around dental ultrasonic scaler tips using a high-speed camera and a zoom lens. We also calculate the area of cavitation using machine learning image analysis. Open source software is used for image analysis. The image analysis presented is easy to replicate, does not require programming experience, and can be modified easily to suit the application of the user.