Cavitation occurrence around ultrasonic dental scalers

Abstract

Ultrasonic scalers are used in dentistry to remove calculus and other contaminants from teeth. One mechanism which may assist in the cleaning is cavitation generated in cooling water around the scaler. The vibratory motion of three designs of scaler tip in a water bath has been characterised by laser vibrometry, and compared with the spatial distribution of cavitation around the scaler tips observed using sonochemiluminescence from a luminol solution. The type of cavitation was confirmed by acoustic emission analysed by a 'Cavimeter' supplied by NPL. A node/antinode vibration pattern was observed, with the maximum displacement of each type of tip occurring at the free end. High levels of cavitation activity occurred in areas surrounding the vibration antinodes, although minimal levels were observed at the free end of the tip. There was also good correlation between vibration amplitude and sonochemiluminescence at other points along the scaler tip. 'Cavimeter' analysis correlated well with luminol observations, suggesting the presence of primarily transient cavitation.

Sonochemical characterisation of ultrasonic dental descalers

“…Experimental considerations meant that this was performed with the tip immersed in the terephthalate solution although removed before analysis. There was a linear dependence of radical production with time although the rates, shown in Table 1, were different for the different tip designs confirming previous observations [10]. The levels of radical production are comparable [15] with those produced by a typical 20 kHz sonochemical horn, albeit in a smaller volume of solution than would normally be involved.…”

“…Luminescence is also observed near the free end of the tips in contrast to the observations in solution. When operated with the tip immersed in solution, emission is confined to particular regions along the length which, as previous work showed [10] correspond to the regions of maximum vibration. The results for the 'A' and 'P' tips are broadly similar although the volume over which luminescence is observed is more closely associated with the tip surface in the latter.…”

“…Hydroxyl radical production around dental descalers has been reported [10,11] but this was conducted with the descaler tips immersed in luminol solution. In clinical use, the descaler will often be used in air around or in contact with teeth.…”

“…As expected, ink was removed from the area in contact but with the A tip, significant removal was also seen near the centre of the tip even though there was no contact. This corresponds to the region of the tip where cavitation is maximised [10,11].…”

“…Previous work [10,11] showed that acoustic cavitation could be produced around descalers and that its spatial distribution depended in detail on the design of the tip; three different designs were found to give markedly different patterns of cavitation. The degree of cavitation, determined by using sonochemiluminescence from a luminol solution, was correlated with the vibratory motion of the tips characterised by scanning laser vibrometry, SLV, which measures motion of an object by monitoring the Doppler shift of a reflected laser beam.…”