On the other hand the high viscosity will increase drag on the microbial cell and increase the shear force. The increased velocity and thus increased shear will inhibit accumulations of cells. As plaque builds up it experiences greater shear which inhibits development. However, even so-called smooth surfaces of teeth contain imperfections, either areas of erosion or areas where prisms meet the surface perpendicularly. These may provide some shelter from shear force but are not usually sufficient to allow for significant plaque development.
Shear force exerts a major influence on plaque development.
It effectively limits it to sites in the mouth which are sheltered from the flow of saliva. Although bacteria can be isolated from all dental surfaces, significant amounts of plaque only accumulate at three sites which experience relatively little or no shear force. Given time, gum-margin plaque can develop to the point where it begins to overgrow the smooth areas of teeth in the direction of the crown. The ability of plaque to grow over smooth areas of the tooth speaks volumes for the tenacity of its adhesive and cohesive properties. Where caries develops The distribution pattern of dental caries closely follows that of plaque.