Colonisation by pioneer species 2. Secondary colonisation 4. Soft tissue has the added advantage in that surface layers exfoliate carrying with them adhering bacteria. This is the main reason why biofilms fail to develop on epithelial surfaces in the mouth even though cells can have 100-200 adhering bacteria . Shear force Microbes free in saliva are carried around the mouth by saliva flow.
Adhesion occurs when the cell comes into contact with a surface.
The current view is that adhesion is a two-stage event. Initially a cell is held a short distance, approximately 10nm, from the surface by a combination of electrostatic and van der Waal's forces. In the second stage this initial, weak attraction, is firmed-up, by multiple adhesion mechanisms which may include synthesis of polymer. The flow of saliva over a surface creates a shear force which tends to remove the microbe from the vicinity of the surface or detach those which are being weakly held. Saliva flows at relatively high velocities, however, near surfaces the flow is reduced by viscosity which increases drag.