Microbial tribology and disruption of dental plaque bacterial biofilms

We investigate tooth wear in the context of removing dental plaque biofilms from tooth surfaces using high velocity water droplets. A laboratory model system was designed using a dextran gel as a biofilm surrogate and a typodont model was used to reproduce the geometry of the mouth. Using uni-axial compression, the elastic modulus of Streptococcus mutans biofilms was 0.280 kPa (±0.350; n=30), and the relaxation time was 11 s (±12; n=10). The type of surface, concentration of sugar, chelation and osmotic pressure all had significant effects on biofilm stiffness. However, there was no direct relationship between biofilm stiffness and surface hydrophobicity or roughness. The elastic modulus of the gel was 17 kPa (±12; n=3), and the relaxation time was 15 s (±12; n=3) which was in the reported viscoelastic range of real bacterial biofilms. High velocity 115 μL water drops travelling with an exit velocity of 60 m/s were generated using a prototype interdental cleaning device (Sonicare AirFloss). High-speed imaging showed that the gel was removed within approximately 6 ms of impact by adhesive failure from the tooth surface and within approximately 26 ms of impact by cohesive failure.

► High velocity micro drops were used to remove model interproximal dental biofilms.
► Uni-axial testing characterized S. mutans and hydrogel biofilm viscoelasticity.
► The stiffness of S. mutans biofilms could be chemically manipulated.
► Micro drops with a velocity of 60 m/s were created by a prototype Philips AirFloss.
► The gel biofilm was removed within 26 ms by adhesive and cohesive failure.