Interproximal cleaning is produced by a combination of fluid droplets producing a certain impact shear stress on the interproximal biofilm combined with shear stress created by the effect of air driving a liquid film (18, 20) in the interproximal surfaces. The shear stress created by the droplets decreases with the depth of the interproximal space, while the shear stress produced by the air-driven liquid film increases with interproximal depth. The combined shear is at least as great as the shear stress necessary to remove biofilm from the interproximal surfaces.