High velocity micro water sprays create ripple formations in S. mutans biofilms with potential for disrupting acidic and anaerobic gradients

Objectives: High velocity micro water sprays generated by the Philips AirFloss designed for cleaning the interproximal (IP) space have been clinically shown to remove significant amounts of plaque and reduce gingival index. Our objective was to use high speed imaging to measure the effect of the sprays on the speed of removal and characterize ripple formation in Streptococcus mutans dental plaque biofilms.
Methods: Microscope slides colonized with 3-days old S. mutans biofilm grown in a mucin and sucrose medium were placed inside a plastic IP model. The biofilms were exposed to high-speed water microspray or air microburst with a velocity of 48.7 m/s,over a burst time of 60.3 ms. The ripple velocity, wavelength, and periodicity were measured by image analysis. To simplify the fluid dynamics biofilms were also exposed to well-defined air jets at velocities ranging from 7.2 to 110.2 m/s.
Results: On impact ripples formed withn ms and migratied at the fluid-biofilm interface with velocitties up to 2.69 ± 0.07 m/s. Immediately after the burst the ripples began to dissipate, leaving little trace of their formation. Mathmatical analysis using a classical linear stability model suggested that the ripples were interfacial instabilities causing the generation of turbulence in the biofilm itself.
Conclusions: The discovery of transient ripples-like structures provides further insight into the mechanical behaviour of biofilms as complex liquids. In addition, this phenomenon may be exploited to disrupt cariogenic acidic microniches and anarobic pathogens thus providing therapuic benefit even adjacent to the areas from which biofilm was phyically cleared.