Identifying cavitation around dental ultrasonic instruments

Ultrasonic instruments are used in clinical dentistry for removing deposits from teeth (scaling) and for cleaning the internal root canal structure. Cavitation is produced in the associated water supply, which may also assist in the cleaning process. The aim of this study was to correlate ultrasonic probe oscillation with cavitation output and to determine its potential clinical usefulness. Scanning laser vibrometry was used to measure the movement of the tip and to locate vibration nodes / anti-nodes at different generator power settings and contact loads (100g and 200g). Cavitation mapping was performed with luminol solution and recorded with a digital camera (Canon EOS 30D). A stereomicroscope captured the real time oscillatory motion and bubble activity to identify the areas of cavitation. The ultrasonic scaler has a free antinode at the tip, which gives the highest displacement amplitude, with a second antinode located approximately 9.1mm further up the tip. The emission of luminol recorded during operation indicated high cavitational activity occurred mainly around the second antinode of the probe with little or no activity at the tip. These emissions changed in intensity during loading of the tip. Mapping of the cavitation was confirmed by daylight stereomicroscope photography. Conclusion: Cavitation around ultrasonic scalers is present predominantly around the body of the probe and not at the tip. This has implications from a clinical viewpoint, as it would be more beneficial for the cavitation to occur at the tip.