Purpose: To investigate the role of sonic acoustic waves and related phenomena in removing a model plaque from a surface, and to determine if there was an optimal frequency for sonic-type toothbrushes.
Methods: A mechanical system was built in which submerged biofilms of Streptococcus mutans were exposed to sonic energy in the range from 80 to 1,000 Hz. The system was calibrated by an accelerometer and pressure transducer, and biofilm removal was measured by optical techniques.
Results: The results showed that the removal was a strong function of the acoustic intensity, but there was no significant dependence upon frequency. Biofilm was removed in very small amounts (up to 2% in 10 minutes) due to acoustic energy in the absence of convective fluid flow, even at high acoustic intensities. When the acoustic action was coupled with convective fluid flow, caused by the piston and well geometry, up to 80% of a biofilm was removed at a calculated acoustic intensity of 27 W/cm2 in 2 minutes. When gas bubbles were entrained in the fluid, the removal approached 100% under intense sonic conditions. With respect to removal of plaque on teeth, the vigorous action of flowing fluid and bubbles is expected to remove plaque, and a maximum fluid velocity is recommended rather than a particular frequency.