Interfacial instability generation in dental biofilms by high-velocity fluid flow for biofilm removal and antimicrobial delivery

Abstract

Oral biofilms play an important role in the development and the persistence of caries, gingivitis and periodontitis. The addition of antimicrobials to toothpastes and mouthwashes combined with biofilm mechanical disruption through dental cleaning devices is the most common way to control oral diseases. However, biofilms’ complicated structure increases their resistance to antiplaque and/or antimicrobials by limiting the diffusion of dentifrices into and inside the biofilm. Studies showed that fluid-dynamic activity generated by power toothbrushes can enhance mass transfer inside the remaining biofilm compared to simple diffusional transport. Microsprays have the advantage in that they are low volume but also have an air/water interface which facilitates biofilm removal. The role of the hydrodynamics in the enhancement of dentifrices inside the biofilm has become a topic of interest since it has been shown that mechanical perturbation caused by fluid-dynamic activity can significantly weaken biofilm structure.

Here we showed that high-velocity microsprays enhance microparticles penetration and Chlorhexidine and Cetylpyridinium chloride antimicrobial activity inside Streptococcus mutans dental biofilms through the generation of hydrodynamic deformations. Using highspeed camera videography, we documented S. mutans biofilm extremely transient fluid behavior and the generation of ripple-like structures at the biofilm/fluid interface when exposed to water microsprays. Mathematical modelling demonstrated that ripples were Kelvin Helmotz Instabilities suggesting the development of fluid-like turbulent mixing in biofilms. Shear stresses generated at the biofilm/burst interface might have enhanced beads and antimicrobials delivery inside the remaining biofilm by combining forced advection into the biofilm matrix with the mixing of the biofilm itself. This project provided further insight into the mechanical behaviour of biofilms as complex liquids and how high-shear fluid-biofilm interaction can be induced to modulate biofilm survival and tolerance.

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ORCID for Paul Stoodley: orcid.org/0000-0001-6069-273X

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