Sonochemical Characterisation of Dental Ultrasound Instruments

Objectives: Ultrasonic scaling instruments are used in dentistry to remove plaque and calculus from tooth surfaces. Their primary cleaning action is the vibratory motion, but cavitation, occurring in the cooling water may also aid in the cleaning process. The aim of this work was to show where around the operating scaler tips inertial cavitation occurs through the use of luminol, a chemiluminescent indicator. Methods: Areas of cavitation in a solution of luminol luminesce blue, with greater cavitation intensity displayed by more intense luminescence. The luminescence is initiated by low concentrations of hydroxyl radicals, which are formed during inertial cavitation bubble collapse. Three designs of piezoelectric ultrasonic scaling tip were assessed (P, PS and A) under unloaded conditions. A solution of luminol was used to fill a glass tank and, in turn, each of the tips was fully immersed within the solution. Tips were operated at a variety of power settings from 1 to 10 (minimum and maximum power, respectively) for 30 seconds. Photographs of the luminescence were taken in low level lighting conditions, and image analysis tools used to examine the luminescence intensity. Results: This work gives a unique insight into the spatial distribution of cavitation around the working ultrasonic tip. It has been suggested that the cavitation occurs primarily at the terminus of the instrument where the maximum vibration amplitude occurs. The results of this work show that cavitation production is at a maximum further up the tip, near the bend of the instrument. Different designs of tip require greater power settings for cavitation to be initiated. Conclusions: Work is underway to characterise the occurrence of cavitation under more clinically realistic loaded conditions. Preliminary results show that luminescence intensity is reduced by half when tips are contacted against a glass surface.

Supported by EPSRC grant nos EP/C536908/1 and EP/C536894/1