Introduction Biofilms may show varying adherence strengths to dentine. This study quantified the shear force required for the detachment of multispecies biofilm from the dentine using fluid dynamic gauging (FDG) and computation fluid dynamics (CFD). To date this force has not been quantified.

Methods Multispecies biofilms were grown over 3, 7 and 14 days on 2 mm thick dentine sections of human molars (n = 8 per group). The FDG technique with different suction flow rates (100%, 80% and 40%) was used to assess biofilm removal. At maximum suction (100%), the flow rate was 500 mL/min. Digital images of each stained dentine sample were captured (10× magnification) before and after subjecting the samples to the various suction flow rates. The change in colour saturation versus control (△E) value was determined to assess removal of biofilm using digital softwares (Image J© and Colormine©). The imposed shear forces were then estimated using CFD and correlated with the △E values.

Results FDG and CFD analysis showed that complete removal of biofilm by using water as the gauging liquid was not possible across any of the experimental groups. Three-day biofilms required significantly lower shear forces for removal than 7-day or 14-day biofilms.

The maximum shear forces were seen in the 14-day biofilm group at all flow rates tested.

When assessing for residual biofilm on the dentine, the △E value showed residual biofilms of approximately 40% at all time periods at a 100% flowrate. Complete removal of multispecies biofilm was not possible in any experimental group.

Conclusions This study for the first-time records forces needed to remove polymicrobial biofilms form the surface of a dentine sample. Within the limits of this study, mature biofilms require greater shear forces for removal. This is important when planning protocols for biofilm removal.