A study to determine whether cavitation occurs around dental ultrasonic scaling instruments
Introduction
Ultrasonic scaling instruments, used in dentistry, operate at frequencies between 25 and 30 kHz. The primary cleaning action of these instruments is attributed to the vibratory motion of the scaler probe. However, another process that may aid in the removal of substances from tooth surfaces is the phenomenon of cavitation, which occurs in the cooling water as it flows over the insert probe [1].
When water is irradiated with ultrasound, OH and H radicals are formed (Scheme 1) due to the high energies generated during cavitational bubble collapse [2]. Cavitation occurring around dental ultrasonic instruments may be quantified by monitoring its chemical effects, using oxidation reactions such as in the Weissler reaction [3] or Fricke's dosimeter and also by direct detection of radical species. However, both the Weissler reaction and Fricke's dosimeter are susceptible to all oxidising species in solution, such as HO2 and H2O2 [4].
The terephthalate dosimeter is a system that measures OH radical yield specifically [4], [5]. The system uses an aqueous solution of terephthalic acid that on reaction with hydroxyl radicals forms 2-hydroxyterephthalate, HTA, (Scheme 2) [5] and is readily detectable using fluorescence spectroscopy [4], [6].
The aim of this investigation was to determine if cavitation occurred around dental ultrasonic scalers and, if so, to estimate the amount of cavitation occurring, using the terephthalate dosimeter.
Section snippets
Materials and methods
A solution of terephthalic acid (TA) was prepared by dissolving, with heating, 0.3323 g (0.002 mol) in 1 dm3 deionised water containing 25 cm3 of pH 7.0 non-fluorescent buffer [4].
Three different styles of tip (3 × TFI-10, 3 × TFI-3, 3 × TFI-1) were used (Fig. 1) in conjunction with a Cavitron SPS ultrasonic generator (Dentsply Preventive Care, York, PA, USA). During normal use, water flows through the handpiece of the scaler and over the length of the tip. Water was required throughout this
Results
Any cavitation that might have been produced by the TFI-1 tips was below the limit of detection (<10−8 M) at all powers. Likewise, any cavitation produced by the TFI-3 or TFI-10 scaler tips at low generator power setting for up to 5 min sonication was also below the limit of detection (<10−8 M). No cavitation was detected at medium power for the TFI-10 tips (2 and 5 min) except for tip 2, which showed very small OH radical concentrations (Table 1). All TFI-10 tips produced cavitation at the
Discussion
This work has demonstrated that chemical reactions resulting from cavitational activity do occur around dental ultrasonic scaler tips under certain operating conditions and is in agreement with previous work [3]. Tip shape and generator power setting were both shown to have an effect on radical production.
The geometry of the scaler tips affects the magnitude of their vibration displacement amplitude. The TFI-10 and TFI-3 style scaler tips have greater vibration displacement amplitudes, at a
Conclusions
This investigation has demonstrated that under certain operational conditions cavitation occurred around dental ultrasonic scalers. The terephthalate dosimeter method was effective in measuring hydroxyl radical concentration produced due to cavitation from scaler tips. Increased cavitational activity occurred at higher power settings and with increased operating time. The TFI-3 tip working at high power resulted in most cavitational activity. The dimensions of the tip and the generator power
Acknowledgements
This project was funded by EPSRC grant no. GR/R82050/01.
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