Zinc and Arginine Treatment Mechanically Destabilizes Dental Biofilms

Objectives: Aims: Mechanical removal of dental-plaque is augmented with therapeutic compounds to promote oral health. We therefore sought to understand how a dentifrice, with zinc and arginine impacted the mechanical properties of biofilms, with the objective of determining if changes to biofilm rheology can enhance dental-plaque removal.
Methods: Methods: Biofilms from pooled saliva-plaque, or Streptococcus gordonii were grown for 5 days and treated with either PBS (untreated control),1% zinc alone, or in combination with 1.5% arginine, or with glycine or lysine alone (amino acid controls) for 2 min. To observe changes to biofilm architecture, biofilms were imaged using confocal microscopy. Biofilm mechanical properties were assessed using uniaxial indentation and a novel rotating-disc rheometer assay.
Results: Results: Image analysis revealed that neither treatment with 1% zinc alone, or in combination with 1.5% arginine, impacted cellular biomass, but significantly reduced the amount and distribution of EPS within the biofilm. Uniaxial indentation revealed that both treatments significantly reduced biofilm rigidity, indicating that the mechanical stability had been compromised. Rotating-disc rheometry of S. gordonii biofilms revealed that combined treatment with 1% zinc and 1.5% arginine, led to biofilms detaching from surfaces at lower shear stresses, compared to 1% zinc treated and untreated biofilms. Treatment with arginine alone lead to detachment of S. gordonii biofilms at lower shear stresses, compared to glycine or lysine, which were similar to the untreated control. This indicates that arginine destabilizes the mechanical properties of the biofilm, through biochemical properties specific to this amino acid.
Conclusions: Conclusion: Combined treatment with 1% zinc and 1.5% arginine physically disrupts biofilm EPS, destabilizing the mechanical integrity of the saliva-plaque biofilm, resulting in the biofilm being more suspectable to mechanical removal. Our data support the use of a dentifrice with 1% zinc and 1.5% arginine active compounds as part of daily oral hygiene regimes.